221

Aggressive Centralized and Distributed Scheduling ofDisk Requests

  • Upload
    doannhi

  • View
    225

  • Download
    1

Embed Size (px)

Citation preview

Page 1: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�������������� � �������������������� ����� � �������� "!#����� $&%(')����!��*��)�+�, � ��.- /0��1#!)�����2�

354

68759;:�<>=#?�@ AB7DCFE�GIH�J�CKA;H

L>MONQPIPSR�TIUWV*UXNZY\[)PS]_^_`aNbUIUIRcM NZ[#dFV�TIUINeV*fhgi]_fkjFfZfb`aR�[OUY*glUIm_R�TIRcno]_NbTIR�`pR�[DUWPqgiY\T�UImKRrMOR�s\TXR�RtY*g

u YOvwUIYxTyY�g2zm_NbfZY{PSY\d_mO|}S~ Y\`ad_]KUIR�T��OvwNZR�[FvwR�V�[FM&�[_sxNZ[_R�R�TINZ[KsD�Nb[)�(m_R��y[_NZ�{R�T�P�NbUS|�Y*gl�&NQv�m_NZs�V*[

���\�x�

u YOvwUXY\TWV*f ~ Y\`a`aNbUIUXR�R{�zTIY�giR�PIPSY\T��(V�fZR����FzV*UXU�� ~ mFV�NZTzTIY�giR�PIPSY\T���MO��V*TWM��F� u Vc�ONQMKP�Y\[zTIY�giR�PIPSY\T��qTXR��{Y\T��r�K�&]FMDsxRzTIY�giR�PIPSY\T���R�[FPIV�fZf u �_��NeP�R� NQv�m_NZR���V*TX|{�h�{UIYxT�V�s\R�LyTWv�m_NbUIR�v�U�� u Nbs\NbU�V*f.�2n{]_NZdK`aR�[OU ~ YxTIdFY\TWV*UXNZY\[

Page 2: Aggressive Centralized and Distributed Scheduling ofDisk Requests

~ Y\dO|DTXNZsxmDU��\]_[KR ���\�x�

Page 3: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� 6¢¡�£¥¤��§¦¥£

¨&©ª©5«x¬O­*­�®°¯±¬³²´¬oµ.¶�«\·F¸°®S¹O¬Dº�·FµBº¼»&®S­�¶�«*®¾½�¿2¶x¬OºÁÀ�Â*ÃB¬Oºl¿2¸°®¾µ2©Ä5Å »&®S­�ƧÇ#¬OÈq¿B¬O­c¶x­

½.ÉÊ «�¿(ÂO¬�Ë�ÌÍ Ä «�¶�Ã2®°µB©5¶ Ä µ

~ mFV�NZT��0�BV*fbR��r�_zV�UIU

u NQPSÎ"TXR�n{]_R�P�U�PXv�m_RcMD]_fZNb[_s#NQP�V&v�TINZUXNQv�V�f2R�fZR�`pR�[DU�Y�g�m_NZsxm_Ïid5R�T�giY\TX`#V*[ÐvwRav�Y\`ad_]KUIR�T�P�|KP�UXR�`ÑMDR�ÏP�Nbs\[���zlTXR��ONZY\]ÐPyMDNeP�Î)PIv�m_R�MO]_fZNb[_s�TIR�PSR�V*TWv�m#NeP(NZ[FPS]DÒ#v�NZR�[OU�^FR�v�V*]ÐP�RrNbU�]FP�RcPyPSNZ`ad_fbNQPSUINQv�Y\T�Y\]KU�M_V�UIR�MMDNeP�Îa`aYOMOR�fQP��D]_[_TXR�d_TXR�P�R�[OU�V�UINb�{Rt�(YxTIÎOfZY{VxM_Pw�FV�[FMÓNb[FV\MOR�no]ÐV*UIR�dFR�T�giYxTI`#V�[FvwRt`aR�UITINev�Pw�.�(m_NePyMONQPIPSR�TIÏU�V�UINbY\[#R�ÔOd_fZYxTIR�P2UIm_R�MONQP�ÎpPIv�m_R�MO]_fZR�TBMDRcP�NZsx[#P�dÐV\vwR�V*[ÐMÕdKTIY��DNeMDR�P2s\]_NeMDR�fZNb[_R�PÖgiY\T�v�Y\`ad_]KUIR�T2PS|_PSUIR�`R�[_sxNZ[_R�R�T�P��(×yY�P�UXÏØ^FVxP�R�M�V�[FM&MONQP�ÎOÏi^FV\PSR�M&vwR�[DUXT�V*fbNZÙ�RcMaPIv�m_R�MD]KfZNZ[Ks�V*TIR�vwYx`adFV�TIR�Ma��NZUXm�MDNeP�UXTINZ^K]_UIR�MPIv�m_R�MO]_fZNb[_s_�BV"[_R��ÚdFV*TWV\MDNbs\` ��NZUXm�vwY�P�U���vwY\`adKfZR�ÔONZUS|{��V*[FMÛd5R�T�giY\TX`#V*[ÐvwR)V\MD�xV*[OU�V�s\R�P��¼Ü°[�MONQP�ÏUITXNZ^_]KUIR�M�PXv�m_RcMD]_fZNb[_s_�xNZ[FMDNb�DNeMD]FV�fFMDNQPSÎ�PXv�m_RcMD]_fZR�T�PÖfbYOv�V*UXR�M V�U2` ]_fbUINbd_fZR2dFY\Nb[DUWP�V�fZYx[_srUXm_RtÜIÝxÞßdFV�UImvwY{Yxd5R�T�V*UXRrUXY `#V�Î{RtPXv�mKR�MD]_fbNZ[_s�MDRcvwNQPSNZY\[ÐPw�

�Ov�m_R�MD]_fbR�T2NZ`adKfZR�`�R�[{U�V�UINbY\[FPV�TIRtR��\V�fZ]FV�UIR�M�]FP�Nb[_s�V�MDR�UWV*NZfbR�M�P�NZ`�]_feV*UIYxT2vwYx[DUWV*NZ[KNZ[_s��\V�fZNeM_V*UXR�M`aYOMDR�fQPyY�g�P�U�V�UIR�ÏiY*giÏiUImKR�Ï°V�TIU�m_Y{PSU�P�|KP�UXR�`#P���vwY\[OUITXY\fbfZR�TWPw��^_]FPSR�Pw��V*[FM¥MONQP�ÎàMDTINb�{R�Pw���(m_RÕP�NZ`�]_feV*UIYxTNQP�MOTINZ�{R�[Ó��NbUIm#R�ÔOUIR�[ÐP�NZ�{R�UITWV\vwRcP;Y�g2TIR�V�fZÏi�(YxTIfQM#PS|_PSUIR�`áV�[FM&MONQP�ÎÕV\vwUXNZ�ONZUS|{�OV*[FM#NZU�TXR�dFY\TIUWPyPS|_PSUIR�`dFR�T�giYxTI`#V�[FvwR�`aR�UITXNQv�P } R{�âs_�b�FV*d_d_fbNQv�V�UINbY\[�TI]K[�UINZ`pR�P��2Nb[�V\MKMDNZUXNZY\[�UXYaUITWV\MDNbUINbY\[FV�f2MDNQPSÎ)P�]_^FPS|_PSUIR�``aR�UXTINev�P } R{�âs_�Z�O`aR�V�[aTIR�n{]_R�PSU�TIR�PSdFY\[FPSRrUINb`aR�P����

Ü°UNQPPSm_Y���[�UImFV�UgiY\TUXm_R�^FR�P�U2PS|_PSUIR�`ãdFR�T�giYxTI`#V�[FvwR{�xPIv�m_R�MD]KfZNZ[KstV�fZs\YxTINbUIm_`#P�`�]FP�U�Nb[FvwY\TXdFY\T�V�UIRP�|KP�UXR�`aÏifZR��{R�f�NZ[DgiYxTI`#V�UINZYx[ } R{�âs_�b�hTIR�n{]_R�PSUtd_TXNZY\TXNZUXNZR�P����a�Ov�m_R�MD]_fbNZ[_s)V�fZs\YxTINbUIm_`#P�UImFV�U�giYOvw]FPtYx[¥TIR�ÏMD]Fv�NZ[_säP�R�R�Î�MOR�fQV�|KP�MOY�[_Y\UB[_R�R�M R�ÔDUXR�[FP�Nb�{R�MDNQPSÎDϾP�dFR�v�Nåjªv�NZ[DgiYxTI`#V�UINbY\[���æÖNZ[FV�fZfb|{�{V*fbs\YxTINZUXm_`#P`�]FP�UR�ÔOd_fZYxNZU�V MDNeP�ΪçèP(Yx[_ÏØ^FY�V*T�M�v�V\v�m_RtUIYpV\v�m_NbR��{RyUXm_R�fZY��(RcP�U�MDNeP�Î#PSR�TI�ONQvwR�UINZ`pR�Pw�

LtM_MDNbUINbY\[FV�f\s\]KNQMDR�fbNZ[_RcPhV*TXR(d_TXY��DNeMDR�M;giYxT.MDR�V*fbNZ[_s���NbUIm�MDNeP�Î�MDTINb�{R2vwY\`p`#V*[FM�n{]_R�]_R�P���P�R�n{]_R�[OUINeV*fMDNeP�ÎaTXR�no]KR�P�U�Yxd_UINb`aNZÙ�V�UINbY\[FP��DV�[FM&MONåéªR�TIR�[DUBY\[_Ïi^FY{V*TWM�v�V\v�m_R�vwYx[DjFs\]KT�V*UXNZYx[FPw�

Page 4: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��Y `�|rg¾V*UXm_R�T�� u Y\[FV�fQMh�DgiYxTyUXR�V\v�m_NZ[Ks�`aRyUXYaV�fZ��Vc|KP�jF[_NeP�m#��mFV�UtÜBP�U�V�TIU�êUIY�`�|�`aY\UXm_R�T��O��V�TIs\NbR{�DgiY\T�mKR�T�R�ÔKV*`ad_fbRyY�gBV�fZNågiR�jFfZfbR�M ��NZUXm)vwY\`adÐV\PIPSNZYx[�êUIY�`�|�P�NQPSUIR�T��_�fZNbÙ�V*^FR�UXm��DgiY\T�^FR�Nb[_s�` |�UXTI]_R�PSU(giTINbR�[FMhêUIY�`�|�V*]_[OU�P��F��V*TINbfZ|O[#V*[ÐM&ë(R��{R�TXfZ|{�\giYxT�UIm_R�NbT�vwY\[OUINb[D]ÐV*fhsx]_NQMKV*[FvwR�V�[FMÓR�[OUImO]FPSNQV\PS`�êV*[ÐMÓUIY�`�|���NågiR{�K�{V*[_R�U��DgiY\T�m_YxfQMDNb[_s�` |�mFV�[FMÓ]K[DUXNZfhUXm_R�R�[FMaY*glUINZ`pR{�

NZN

Page 5: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�0��ì í îÚï ðòñó� ôÑñóõ ñóí ö÷$

�&| giTINbR�[FM_PBV*[FM#fQV�^_`#V*UXR�P(V�UyUXm_R��y[_Nb�{R�T�PSNZUS|rY�gB�&NQv�m_NZs�V*[amÐVc�{R�^5R�R�[&UXm_R�P�Nb[_s\fbR�^5RcP�U�V\P�dFR�v�UY*gB`�|as\TWV\MD]ÐV*UIRpPIv�m_Y{YxffZNkgiR{��ÜyV�`øMOR�R�d_fb|ÓUXmFV*[KÎogi]_f�UIYa`�|#V\MO�DNeP�Y\T�� u T��5�BV*fbR�zV�UIU��5giY\Tt`ÕV*ÎONZ[_s`aRpVÓdFV�TIU�Y�gtm_NeP�UXNZs\mOUIfb|DÏiÎO[_NZU�TIRcP�R�V�T�v�m"sxTIY\]Kd��¥ÜymÐVc�{RpUIm_YxTIY\]Ks\m_fb|¥R�[\ùSY�|{R�M�` |)dFR�T�PSY\[FV�f�V*[FMd_TXY*giR�PXP�NZYx[FV*f�V\PXP�YOvwNeV*UXNZY\[���NbUIm¢UIm_R)`aR�`�^FR�T�PtY�grUXm_R#s\TXY\]_d���Nb[FvwfZ]ÐMDNZ[_sú�&NbÎ{R#ë(]_UXfZR�T��2zÖY\Ïi�2]_[_s~ mFV�[_s_� ~ m_TXNQP��^FR�TIfb|{� ~ V�TIfbY{P�æ_]_R�[OUIR�P��_ûyTXR�saû�V*[_sxR�T��F�TXNQvt×tV�Y_� � Y\^FR�TXU�×yY\]��K�hR�V*Ͼ×y��V*[_sp�hR�R{�u R�[K[_NQP���V�T�PIVO�;�oV*[\ùXV�|ÛzV�UIR�f¾�2�TINQv#�{d_T�V�[_s\fbR{�B�{V*TIRcMü��U�V*TXÎh�BV*[ÐMò��PSR�Ïi��]Û�2R�m��úÜ°[ÛdFV*TXUINevw]_fQV�T��û�TIR�s#û�V*[_sxR�T�mFV\P�^FR�R�[#NZ[FPSUITX]FvwUIYxT��Od_]_d_Nbf°�FV*[ÐMÕgiTINbR�[FM UXY `pRyUXm_TIYx]_s\m_Yx]_UtYx]_T�ùSYxNZ[OU�zm u no]_RcP�U��

Þ�]_T#V\MO`aNZ[_NeP�UXT�V*UXNZ�{R)V\PXP�NeP�U�V�[DU��t�&Nev�m_R�fZfZR ~ mFV*d_`ÕV*[���mFV\P dKTIY��DNeMDR�MßR�ÔKvwR�fbfZR�[OU�PS]_d_dFY\TXU)V*[FM[_R��{R�TIÏiR�[FMDNb[_s�dFV*UXNZR�[Fv�R�MD]_TXNZ[_s�UIm_RtfeV\PSU(giR���|{R�V*TWPw��zV*]_feV u R�[OUIYx[�� u R�[_NQPSR u ])zTINZR��DV�[FM#�\R�V*[K[_RzV�UIUIR�T�P�Yx[ÓgiYxTI`aR�MpV�P�ÎONZfZfbR�MaPSR�vwY\[ÐMÕfbNZ[_R�Y�g2MDR�giR�[FP�R�V�s{V*Nb[FP�U�s\R�[_R�T�V�f.vwY\[Ogi]FP�NbY\[�V�[FMÓTXR�MDÏiU�V�d5R��

�2MD��V�T�M u Vc�ONQMKP�Y\[±� � NQv�m_NZR���V*TI|��h��TIR��{YxT��&]FMDsxR{�FV*[FM)�tR�[FPIV�fZf���NeP�R�mFV��{R�` |pP�Nb[FvwR�TXRts\TWV*UINbÏUI]ÐMDRrgiY\T�PSR�TI�ONZ[Ks Yx["`�|#MDYOvwUXY\TWV*f2vwYx`a`aNbUIUIR�R\���(mKR�NZT�v�Y\`a`aR�[{U�P�V*[ÐM�P�]_sxs\R�PSUINZYx[FPt]_[FMDYx]_^_UXR�MDfZ|NZ`pd_TIY��{R�M�UIm_R�n{]FV*fbNZUS|�Y*g�` |�MDNePIPSR�TIUWV*UINbY\[��

Üt�(Y\]KfQM"fbNZÎ{R�UIY�UXmFV*[KÎ¥�\Yxm_[¢æÐYxT�MDR�` ��V*fZU�� � NQv�mFV*TWMòû�Y\fQMONZ[_sK� � Nev�m_NbR���V*TX|{�2�&NZÎ{R��hR�Yx[FV*TWMh�~ m_TXNQP � ]KR�`a`afbRwT�� ~ V�TIf��{U�V�R�fZNb[��{�(Nb`÷�{]_fZfbNZ�xV*[±� u Y\]Ks�ý�YxNZsxmDU��{V*[FMp�\Y\m_[a��NbfZÎ{R�P�giY\T2UIm_R�NZTd_TXY*giR�PSÏP�NbY\[FV�fDsx]_NQMKV*[FvwR�V*[FM�NZ[FPSNZsxmDUWPw�ÜFUImFV�[_Î��\NZ`ózNbÎ{R�Y�gªL2��þ��yÝ\û�ÜI�ygiY\T.d_TXY*�ONQMONZ[_s�UIm_R2Nb[_NZUXNQV*f\gi]K[FMDNZ[KsgiY\T�` |aTXR�P�RcV*T�v�múV*U�UIm_R��y[KNZ�{R�TWP�NZUS|aY�g��&NQv�m_NZs�V*[���Ü�V�fQP�Y#UXmFV*[_Îà×yR���fbR�UIUXÏ°zVxv�ÎxV�T�Mh�ªL2��þ��yÝxû�ÜW�Ð��OvwNbR�[OUINåj5v�V*[FMa�[_sxNZ[_R�R�TINb[_s��{Y*giUS��V�TIR{�KV*[FM u NZsxNZU�V�f��2n{]_NZd_`pR�[DU ~ Y\TXdFY\T�V�UINbY\[agiY\TBd_TIY��ONQMDNb[_s�VxM_MDNZÏUINbY\[FV�f�R�n{]_NZd_`pR�[DUBV�[FM jF[FV*[ÐvwNQV�fPS]_d_dFY\TXU��

æÖNZ[ÐV*fZfb|{�OÜ��BY\]_feMÕfbNZÎ{R�UIY�UImFV�[_ÎaUXm_R��\V�TINbY\]FP�V�[_NZ`#V�UIR�MpV*[FM)vwY\`aNevyv�mFV�T�V\v�UIR�TWP�UImÐV*U�mFV��{RtÎ{R�d_U`aR�PXV*[_R��(�(m_R��(Nev�Ϊ�_LyTXUImO]_T��KV*[FM)V*fbf�UIm_R�Y\UXm_R�T�PS]_dFR�TIm_R�TIY{R�PyNb[)�(m_R ~ NZUS|hê ~ V*fb�DNb[&V�[FM&×�Y\^_^FR�P�êu NbfZ^FR�TIU�� u Yxs\^FR�TIU�� ~ V�UI^FR�TIU�� � V*UX^5R�TIU���V�[FMÁ�8V*fbfZ|ªê��(m_Rú�y[Fv�V�[_[O|òÿ�Ï°�&R�[±êtë(TI]KR"�{d_fb]FvwR } `�|ÿtϾzNZfZYxU�V�fZUIR�TIÏiR�s\YO��êyÞ�d_]FP��(ë(NbfZf2UImKR ~ V�U��BV*[FM¥UXm_R#TIR�PSU�Y*g�UIm_R#ë(fbY{Y\` ~ Yx]_[OU�|FÝ\Þ�]_UXfQV�[FM¥s{V*[Ks_êë(]_s�Pyë(]_[K[D|ªê u V�éª| u ]Fv�Ϊê_V�[FM&�(�BYa�{UI]Kd_NQM u Y\s�Pw�

NZNbN

Page 6: Aggressive Centralized and Distributed Scheduling ofDisk Requests

öß���÷ðÛñ î�� �áîøí ö ñóí öÚ$

������� ��������� ������� ��� ��������������������� ��� ��������������������� ��� ����� ����� NZN�� �������������� ���!"�����$# ����������������� ��� ��������������������� ��� ����� ����� NbNZN�%��#&�'��()�*�+,����#-��� ��� ��������������������� ��� ��������������������� ��� ����� ����� �DN�%��#&�'��()(��� �.�/��#0� ��� ��������������������� ��� ��������������������� ��� ����� ����� �ONZN 1��32�� ��/4#

� Ü°[DUXTIYOMD]Fv�UINZYx[ � ��� ��������������������� ��� ��������������������� ��� ����� ����� �� � � Þ��{R�TX�DNbR�� � ��������������������� ��� ��������������������� ��� ����� ����� �� �65 �(mKR�P�NeP��{UWV*UXR�`aR�[OU ������������� ��� ��������������������� ��� ����� ����� 5� �67 L�v�vwY\`pd_fZNeP�m_`�R�[OU�PÖY�g2UIm_NeP u NQPXP�R�TXU�V�UINZYx[ ����������������� ��� ����� ����� 7� �98 Þ�TXs{V*[KNZÙ�V�UINZYx[&Y�g2UIm_NeP u NQPXP�R�TXU�V�UINZYx[ � ��������������������� ��� ����� ����� 7

5 �tP�R�gi]_f�Ov�m_R�MD]_fbNZ[_säÜ°[DgiY\TX`#V*UXNZY\[ ������� ��� ��������������������� ��� ����� ����� 85O� � Ü°[DgiYxTI`#V�UINbY\[)æ_TIY\`;:�ë(R�fbY*�=<rUXm_R��Ov�m_R�MD]_fbR�T ������������� ��� ����� ����� 8

5O� � � � �(m_Rä�&YOMDR�TI[ u NeP�Î u TINZ�{R ��� ��������������������� ��� ����� ����� 85O� � �65 Þ�UIm_R�T�ÜWÝxÞãzV*UXm��{U�V�UIR � ��� ��������������������� ��� ����� ����� �?>

5O�65 Ü°[DgiYxTI`#V�UINbY\[)æ_TIY\`;:�Ly^FY��{R�<rUImKR´�ov�m_RcMD]_fZR�T ������������� ��� ����� ����� �\�5O�65O� � Lyd_dKfZNQv�V*UINbY\[)V*[ÐMÓæ.NZfZR��{|_PSUIR�` Ü [OgiY\TI`ÕV*UINbY\[ ����� ��� ����� ����� �\�5O�65O�65 � R�P�Yx]_T�vwR��yUXNZfbNZÙ�V�UINZYx[ ��� ��� ��������������������� ��� ����� ����� � 5

7 � R�fQV*UXR�Ma�"YxTIΠ� ��� ��������������������� ��� ��������������������� ��� ����� ����� � 77O� � �ov�m_RcMD]_fZR�T�ܰ`ad_fbR�` R�[DUWV*UINbY\[FP ��� ��� ��������������������� ��� ����� ����� � 77O�65 �ov�m_RcMD]_fZNb[_s�Lyfbs\Y\TXNZUXm_`#P ������� ��� ��������������������� ��� ����� ����� � 7

7O�65O� � �Ov�m_R�MD]KfZNZ[Ks���NZUIm)Ü°[DgiYxTI`#V�UINZYx[ giTIYx`@:�ë(R�fZY��=< ��� ��� ����� ����� � 87O�65O�65 �Ov�m_R�MD]KfZNZ[Ks���NZUIm)Ü°[DgiYxTI`#V�UINZYx[ giTIYx`@:�L�^5Y��{R�< ��� ��� ����� ����� ��A

7O�67 ��NZs\[KNåjªv�V�[DU � Y{Y\`÷giYxTtÜ°`ad_TXY��{R�` R�[OU ��������������������� ��� ����� ����� 5 >8 �&R�UImKYOMDY\fbY\s\| � ��� ��������������������� ��� ��������������������� ��� ����� ����� 5 �

8K� � �(mKR �{Nb` ]_feV*UXNZY\[p�&YOMDR�f ��������� ��� ��������������������� ��� ����� ����� 5 �8K� � � � ×yY�P�U��&YOMDR�fQP ����������� ��� ��������������������� ��� ����� ����� 5 �8K� � �65 u NeP�Î u TXNZ�{R��&YOMDR�feP ����� ��� ��������������������� ��� ����� ����� 5B5

8K�65 �úY\TXÎDfbY{VxM_P ��������������������� ��� ��������������������� ��� ����� ����� 5 �

NZ�

Page 7: Aggressive Centralized and Distributed Scheduling ofDisk Requests

8K�65O� � u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� 5 �8K�65O�65 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� 5BC

8K�67 �ov�m_RcMD]_fZNb[_s�Lyfbs\Y\TXNZUXm_`#P ������� ��� ��������������������� ��� ����� ����� 5 A8K�67O� � �Ov�m_R�MD]KfZNZ[Ks���NZUIm)Ü°[DgiYxTI`#V�UINZYx[ giTIYx`@:�ë(R�fZY��=< ��� ��� ����� ����� 5 A8K�67O�65 �Ov�m_R�MD]KfZNZ[Ks���NZUIm)Ü°[DgiYxTI`#V�UINZYx[ giTIYx`@:�L�^5Y��{R�< ��� ��� ����� ����� 5 A8K�67O�67 �{R�n{]_R�[OUINeV*f.�{UITXR�V*`øÞ�d_UXNZ`aNbÙ�V*UXNZYx[FP ��������������� ��� ����� ����� 5BD

8K�98 �&R�UITINev�P ��� ��������������������� ��� ��������������������� ��� ����� ����� 5 �� ~ R�[OUIT�V�fZNbÙ�R�MÓ�Ov�m_R�MO]_fZNb[_s�V�UyUXm_R�×yY{PSU ��� ��� ��������������������� ��� ����� ����� 7 >

� � � �ov�m_RcMD]_fZNb[_s���NZUXm)Ü [OgiY\TI`ÕV*UINbY\[#æ_TXY\`@:Wë(R�fZY��=< ����������� ��� ����� ����� 7 >� � � � � �{|O[DUXm_R�UXNQvy�úY\TXÎDfbY{V\MKP ��� ��� ��������������������� ��� ����� ����� 7 >� � � �65 u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� 7�8� � � �67 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� A�>� � � �98 �{]_`p`#V*TX|�Y*g ~ Yx[FvwfZ]ÐP�NZYx[FP � ��������������������� ��� ����� ����� DBC

� �65 �ov�m_RcMD]_fZNb[_s���NZUXm)Ü [OgiY\TI`ÕV*UINbY\[#æ_TXY\`@:WLy^FY*�{RE<�V*[FMF:�ë(R�fbY*�=< ����� ����� DBD� �65O� � u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� DBD� �65O�65 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� D �� �65O�67 �{]_`p`#V*TX|�Y*g ~ Yx[FvwfZ]ÐP�NZYx[FP � ��������������������� ��� ����� ����� � 8

C ~ R�[OUIT�V�fZNbÙ�R�MÓ�Ov�m_R�MO]_fZNb[_s�V�UyUXm_R u NQPSÎ ��� ��� ��������������������� ��� ����� ����� �G>D�CO� � �ov�m_RcMD]_fZNb[_s���NZUXm)Ü [OgiY\TI`ÕV*UINbY\[#æ_TXY\`@:Wë(R�fZY��=< ����������� ��� ����� ����� �G>D�

CO� � � � u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� �G>D�CO� � �65 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� �x� 8CO� � �67 �{]_`p`#V*TX|�Y*g ~ Yx[FvwfZ]ÐP�NZYx[FP � ��������������������� ��� ����� ����� � 5B7

CO�65 �ov�m_RcMD]_fZNb[_s���NZUXm)Ü [OgiY\TI`ÕV*UINbY\[#æ_TXY\`@:WLy^FY*�{RE<�V*[FMF:�ë(R�fbY*�=< ����� ����� � 5B7CO�65O� � u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� � 5B7CO�65O�65 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� � 7 >CO�65O�67 �{]_`p`#V*TX|�Y*g ~ Yx[FvwfZ]ÐP�NZYx[FP � ��������������������� ��� ����� ����� � 8 �

A u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_s ����������������� ��� ��������������������� ��� ����� ����� � 8H5A � � �ov�m_RcMD]_fZNb[_s���NZUXm)Ü [OgiY\TI`ÕV*UINbY\[#æ_TXY\`@:Wë(R�fZY��=< ����������� ��� ����� ����� � 8H7

A � � � � u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� � 8H7A � � �65 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� � C �A � � �67 �{]_`p`#V*TX|�Y*g ~ Yx[FvwfZ]ÐP�NZYx[FP � ��������������������� ��� ����� ����� � C �

A �65 �ov�m_RcMD]_fZNb[_s���NZUXm)Ü [OgiY\TI`ÕV*UINbY\[#æ_TXY\`@:WLy^FY*�{RE<�V*[FMF:�ë(R�fbY*�=< ����� ����� ��A CA �65O� � u NeP�Î � R�n{]_R�P�U���T�VxvwR�P ��� ��� ��������������������� ��� ����� ����� ��A CA �65O�65 æ_]_fZf��|_PSUIR�`Ú�qTWV\vwRcP ��� ��� ��������������������� ��� ����� ����� ��A CA �65O�67 �{]_`p`#V*TX|�Y*g ~ Yx[FvwfZ]ÐP�NZYx[FP � ��������������������� ��� ����� ����� � D �

D ~ Y\[Fv�fZ]FMDNb[_s � R�`ÕV*TIÎKP(V�[FM#æ_]_UI]_TXR u NZTXR�vwUINbY\[FP ������������������� ��� ����� ����� ��� 7DO� � æ_]_UX]_TIR��úY\TXÎ ������������������� ��� ��������������������� ��� ����� ����� ��� C

�2�2�������JIK����������� ��� ��������������������� ��� ��������������������� ��� ����� ����� ��� D+��G+,�%��� �/�32�1�L ��� ��� ��������������������� ��� ��������������������� ��� ����� ����� 5 > 8

Page 8: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ðNM$&ö î�� öß���÷ðÛñ $

��O 3QPSR8_� � ë�V\PSNQv ~ mFV�T�V\v�UIR�TXNQP�UXNQv�P(Y�gUXm_R�×tz ~ 5T5�8 A u NQPSÎ u TXNZ�{R ������������� ��� ����� ����� 5B58_�U5 ×tz¢V*[FM u � ~ u NQPSÎ � R�no]KR�P�U���T�VxvwR ~ mFV*TWV\vwUXR�TINeP�UINev�P ������������� ��� ����� ����� 5BC� � � �OV�`ad_fZR��&R�V*[ � R�P�dFY\[ÐP�R��(Nb`aR�PgiY\T���ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_`ÕP ��� ��� ����� ����� 8H5� �U5 Þ�[_Ïi^5Y�V*TWM ~ V\v�m_R � R�VxM#×yNZU�zÖR�T�vwR�[OU�V�s\R�PgiY\T���ë��yϾë�V\P�RcMÓL�fZs\YxTINbUIm_`#P ����� ����� 8H7� �U7 Þ�[_Ïi^5Y�V*TWM ~ V\v�m_R � R�VxM#×yNZU�zÖR�T�vwR�[OU�V�s\R�PgiY\T�æ_]_fZfbÏ°�t[_Y���fZRcMDs\R�L�fZs\YxTINbUIm_`#P � ����� � D� �V8 zÖR�TWvwR�[OU�V�s\R � R�MD]ÐvwUINbY\[�NZ[ú��Y\UWV*f � R�n{]_R�PSU�P��{R�TI�ONQvwR�M#MD]KR�UIY��{R�n{]_R�[OUINeV*f � R�no]KR�P�U

~ Y\[Ðv�V*UXR�[FV*UXNZYx[ � ��� ��������������������� ��� ��������������������� ��� ����� ����� C �CD� � �&R�V�[ � R�PSd5Yx[FP�Rä�(NZ`aRcPlgiY\T ~ R�[DUXT�V*fbNZÙ�RcMÓ�Ov�m_R�MD]_fbR�T�P ������������� ��� ����� ����� �x� 7CD�U5 �&R�V�[&��Y\[_Ï ~ Y\`adK]_UIR�Y\T � ]_[)�(NZ`aR�PgiY\T ~ R�[OUITWV*fbNZÙ�R�M#�Ov�mKR�MD]_fbR�T�P ��� ����� ����� � 5B5CD�U7 zÖR�TSgiY\TX`#V*[Fv�R��&R�UITXNQv�PgiY\T�LysxR�ÏS�{R�[FPSNZUINb�{R ~ R�[OUITWV*fZNbÙ�R�MÓ�ov�m_RcMD]_fZR�T�P ��� ����� ����� � 7 �CD�V8 �&R�V�[&��Y\[_Ï ~ Y\`adK]_UIR�Y\T � ]_[)�(NZ`aR�PgiY\T ~ R�[OUITWV*fbNZÙ�R�M35XW �Ov�m_R�MD]KfZR�TWP ����� ����� � 8 �A � � �&R�V�[ � R�PSd5Yx[FP�Rä�(NZ`aRcPlgiY\T���ë���Ï°ë�VxP�R�M��Ov�mKR�MD]_fbR�T�P ������������� ��� ����� ����� � C AA �U5 �&R�V�[ � R�PSd5Yx[FP�Rä�(NZ`aRcPlgiY\Tt�oz ~ ��æ��Ov�m_R�MD]_fbR�T�P ����������������� ��� ����� ����� � CBDA �U7 �&R�V�[&��Y\[_Ï ~ Y\`adK]_UIR�Y\T � ]_[)�(NZ`aR�PgiY\T���ë��yϾë�V\PSR�M&�Ov�m_R�MD]_fbR�T�P ��� ����� ����� ��A 8A �V8 �&R�V�[&��Y\[_Ï ~ Y\`adK]_UIR�Y\T � ]_[)�(NZ`aR�PgiY\Tt�Oz ~ ��æ��Ov�mKR�MD]_fbR�T�P ��� ��� ����� ����� ��A��A � � �&R�V�[ � R�PSd5Yx[FP�Rä�(NZ`aRcPlgiY\T�L��Oz ~ ��æ } C{�y�Ov�m_R�MO]_fZR�TWP ������������� ��� ����� ����� � DB7A �UC �On{]FV*TXR�M ~ Y{R�Ò#vwNbR�[OU�P�Y�g2ýBV*TXNQV*UXNZYx[ÕgiYxT�L��Oz ~ ��æ } Co���Ov�mKR�MD]_fbR�T�P � ��� ����� ����� � D�8A � A �&R�V�[&��Y\[_Ï ~ Y\`adK]_UIR�Y\T � ]_[)�(NZ`aR�PgiY\T���ë��yϾë�V\PSR�M�5XW �Ov�m_R�MO]_fZR�TWP ����� ����� ���B>A �UD �&R�V�[&��Y\[_Ï ~ Y\`adK]_UIR�Y\T � ]_[)�(NZ`aR�PgiY\T=5HW �Oz ~ ��æÁ�Ov�m_R�MD]KfZR�TWP ��� ����� ����� ���D�Lr� � zV�T�V*`pR�UIR�TWPlgiYxTt�&YOMDR�fZNZ[Ks�UIm_R�×tz ~ 5B5�8 A Y\[)UIm_R�� ~ � 7 �\�T> PS|_PSUIR�` ����� ����� ���\�Lr�65@YFY\[KR �{dFR�vwNkjªv�V�UINZYx[FP�giY\T�UXm_R�×tz ~ 5T5�8 A � ��� ��������������������� ��� ����� ����� ���\�Lr�67 �{R�R�Î#zV*TWV*`aR�UIR�TWPlgiY\T��&YOMOR�fZNb[_s�UIm_R�×tz ~ 5B5�8 A ������������������� ��� ����� ����� 5 >B>Lr�98 Þ��{R�TImKR�V\M u R�feV�|_P�giYxT��&YOMDR�fZNb[_s�UImKRr×�z ~ 5B5�8 A Yx[&UXm_R�� ~ � 7 �x�B> � ����� ����� 5 >D�Lr� � LtM_MONZUINbY\[FV�f��"TXNZUXRrÞ��{R�TIm_RcV\M u R�feVc|KP�giY\T��&YOMOR�fZNb[_s�UIm_R�×tz ~ 5B5�8 A ��� ����� ����� 5 >D�

�ON

Page 9: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ðNM$&ö î�� �ZMô\[ /0ñ $

(^]S_a`cb R5D� � u NeP�Î u TXNZ�{R���R�TX`aNZ[_YxfZYxs\| ��������������� ��� ��������������������� ��� ����� ����� �5D�U5 �&R�VxP�]_TXR�M&�{R�R�Î ~ ]KTI�{R�P�giYxT�UIm_R��{R�V�s{V�UIR �o��8 � C >D� � u NQPSÎ u TINb�{R � ��� ����� ����� A8_� � �OV�`ad_fZR�ý(V�fZNeM_V*UXNZY\[#�úY\TXÎDfbY{V\M � RcP�dFY\[FPSR��(Nb`aR u NQP�UXTINb^_]_UINbY\[FP ��� ��� ����� ����� 5B7� � � ��ë��yϾë�V\PSR�M�LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwR#]FP�Nb[_sÛVò��|D[OUIm_R�UINQva�úY\TXÎDfbY{V\M���NZUXm��y[KNZÏ

giY\TX`afZ| u NeP�UITXNZ^_]KUIR�M � R�no]KR�P�U��{U�V�TIUINb[_sp�hYOv�V*UXNZY\[ÐP ����������������� ��� ����� ����� 7B5� �U5 æ_]_fZfbÏ°��V�d�V�[FM���ë��yϾë�V\P�RcMrLyfbs\Y\TXNZUXm_`ózÖR�TSgiY\TX`#V*[Fv�R]FP�Nb[_s�Vt�{|O[DUXm_R�UINev�"YxTIÎOfZY{VxM

��NZUXm)�y[_NågiYxTI`afb| u NQPSUITXNZ^_]_UXR�M&�{U�V�TIUXNZ[_sp�hYOv�V*UXNZYx[FP ��������������� ��� ����� ����� 7B7� �U7 æ_]_fZfbÏ°�t[_Y���fbR�MDs\RBLyfbs\YxTINZUXm_`ãzÖR�TSgiY\TI`ÕV*[FvwR�]FP�Nb[_stV��{|D[OUImKR�UINevl�úY\TXÎDfbY{VxM���NZUXm��y[KNZÏ

giY\TX`afZ| u NeP�UITXNZ^_]KUIR�M � R�no]KR�P�U��{U�V�TIUINb[_sp�hYOv�V*UXNZY\[ÐP ����������������� ��� ����� ����� 7 �� �V8 d�egfhfji\����ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ��������������������� ��� ����� ����� 7BC� � � kmlon�p e�����ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ������������������� ��� ����� ����� 7 A� �UC q�rtsguwvyxGz��2��ë��yÏ°ë�VxP�R�M#Lyfbs\YxTINZUXm_`ázÖR�T�giY\TX`#V*[ÐvwR ����������������� ��� ����� ����� 7BD� � A km{ r|uG} k ����ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_`ÚzÖR�TSgiY\TX`#V*[Fv�R ������������������� ��� ����� ����� 7 �� �UD ~^s���eJs��2��ë���Ï°ë�VxP�R�M#Lyfbs\Y\TXNZUXm_`÷z.R�T�giYxTI`#V�[FvwR ������������������� ��� ����� ����� 8 >� � � v�e��oiHsg�i���ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ������������������� ��� ����� ����� 8 �� � �?> d�egfhfji\��æ_]_fZfbÏ°��V�d)V*[FM)��ë��yÏ°ë�VxP�R�M#Lyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ����� ��� ����� ����� 8 �� � �\�-kmlon�p e���æ_]_fZfbÏ°��V�d)V*[FM)��ë��yÏ°ë�VxP�R�M#Lyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ��� ��� ����� ����� 8HC� � � 5�q�rtsguwvyxGz��2æÐ]KfZfZϾ��V*d)V�[FM&��ë��yϾë�V\PSR�M#LyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR � ��� ����� ����� 8 A� � � 7 km{ r|uG} k ��æ_]_fZfbÏ°��V�d#V*[ÐM&��ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ��� ��� ����� ����� 8HD� � � 8�~^s���eJs��2æ_]_fbfZϾ��V*d)V*[ÐMÓ��ë���Ï°ë�VxP�R�M#Lyfbs\Y\TXNZUXm_`ázÖR�TSgiY\TX`#V*[Fv�R ��� ��� ����� ����� 8 �� � ��� v�e��oiHsg�i�æ_]_fZfbÏ°��V�d)V*[FM)��ë��yÏ°ë�VxP�R�M#Lyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ��� ��� ����� ����� �B>� � � C�d�egfhfji\��æ_]_fZfbÏ°�t[_Y���fbR�MDs\R�LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ��������������� ��� ����� ����� � 5� � ��A�kmlon�p e���æ_]_fZfbÏ°�t[_Y���fbR�MDs\R�LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ��������������� ��� ����� ����� � 7� � � D�q�rtsguwvyxGz��2æÐ]KfZfZϾ�t[_Y���fZR�MOs\R�Lyfbs\YxTINZUXm_`ázÖR�T�giY\TX`#V*[ÐvwR ������������� ��� ����� ����� � 8� � ����km{ r|uG} k ��æ_]_fZfbÏ°�t[_Y���fbR�MDs\R�LyfZsxY\TINbUIm_`ÚzÖR�TSgiY\TX`#V*[Fv�R ��������������� ��� ����� ����� �\�� �U5 > ~^s���eJs��2æ_]_fbfZϾ�t[_Y���fZR�MDsxR�Lyfbs\Y\TXNZUXm_`÷z.R�T�giYxTI`#V�[FvwR ��������������� ��� ����� ����� � C� �U5 � v�e��oiHsg�i�æ_]_fZfbÏ°�t[_Y���fbR�MDs\R�LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ��������������� ��� ����� ����� �XA� �U5B5�d�egfhfji\� � � A�� ÿ��h�{R�n{]_R�[OUINeV*fÖ��UITIRcV*`áLyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ������� ��� ����� ����� �\�� �U5B7 kmlon�p e�� � �U5 � ÿ��h�{R�n{]_R�[OUINeV*fÖ��UITIRcV*`áLyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ����� ��� ����� ����� �\�� �U5�80q�rtsguwvyxGz���5D� � ÿ��h�{R�n{]_R�[OUINeV*f��{UXTIR�V�`áLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR ����� ��� ����� ����� C >� �U5 ��km{ r|uG} k ��5D� � ÿ��F�{R�n{]_R�[OUINeV*fÖ��UITIRcV*`áLyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ����� ��� ����� ����� C >

�ONZN

Page 10: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� �U5BC�~^s���eJs�� � � > ÿ��h�{Rcno]_R�[DUXNQV*f.�{UITXR�V*` LyfZsxY\TINbUIm_`ÚzÖR�TSgiY\TX`#V*[Fv�R ������� ��� ����� ����� C �� �U5 A v�e��oiHsg�i� � � > ÿ��F�{R�n{]_R�[OUINeV*fÖ��UITIRcV*`áLyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ����� ��� ����� ����� C �� �U5BD�Ü°`ad_TXY*�{R�` R�[OUtNb[ � R�VxMò×�NZU � V*UXNZY�P´Y�g�æ_]_fbfZϾ��[KY*��fbR�MDsxR&�Ov�m_R�MD]_fbNZ[_sàLyfZsxY\TXNZUImK`#P

MD]_R�UXY ~ Vxv�m_R��t[_Y���fZRcMDs\R ��������������� ��� ��������������������� ��� ����� ����� CB7� �U5 � d�egfhfji\� � � A�� ÿ�� ~ Ï°�ÖÞ�Þ�� zÖR�TSgiY\TX`#V*[Fv�Ry��NbUIm)æ ~ æ2� ~ Yx`a`#V�[FMDÏ�Wy]KR�]_R�M u NQP�ÎKP ��� CBC� �U7 >�kmlon�p e�� � �U5 � ÿ�� ~ Ï°�ÖÞ�Þ�� zÖR�TSgiY\TX`#V*[Fv�Ry��NbUIm)æ ~ æ2� ~ Yx`a`#V�[FMDÏ�Wy]KR�]_R�M u NQP�ÎKP ��� CBC� �U7 � q�rtsguwvyxGz���5D� � ÿ�� ~ Ͼ�ÖÞ�Þ�� zÖR�T�giY\TX`#V*[ÐvwRy��NbUIm)æ ~ æ�� ~ Y\`a`#V�[FMDÏ�W�]_R�]_R�M u NQPSÎ_P � C A� �U7B5 km{ r|uG} k ��5D� � ÿ�� ~ Ï°�ÖÞ�Þ�� zÖR�TSgiY\TX`#V*[Fv�Rt��NZUXm&æ ~ æ�� ~ Y\`p`#V*[FMOÏ�W�]_R�]KR�M u NQP�ÎKP ��� C A� �U7B7�~^s���eJs�� � � > ÿ�� ~ Ͼ�ÖÞ�Þt� z.R�T�giYxTI`#V�[FvwRt��NbUIm)æ ~ æ2� ~ Yx`a`#V�[FMDÏ�Wy]KR�]_R�M u NQPSÎ_P ��� CBD� �U7�80v�e��oiHsg�i� � � > ÿ�� ~ Ï°�ÖÞ�Þ�� zÖR�TSgiY\TX`#V*[Fv�Rt��NZUXm&æ ~ æ�� ~ Y\`p`#V*[FMOÏ�W�]_R�]KR�M u NQP�ÎKP ��� CBD� �U7 ��kmlon�p e�� � �U5 � ÿ�� ~ Ï°�ÖÞ�Þ�� zÖR�TSgiY\TX`#V*[Fv�Ry��NbUIm)æ ~ æ2� ~ Yx`a`#V�[FMDÏ�Wy]KR�]_R�M u NQP�ÎKP ��� C �� �U7BC km�Tl sw��e l �(��ë���Ï°ë�VxP�R�M#Lyfbs\Y\TXNZUXm_`ázÖR�TSgiY\TX`#V*[Fv�R ������������������� ��� ����� ����� A{�� �U7 A d�iH�y�ms�e�xgx����ë��yϾë�V\PSR�M#LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ����������������� ��� ����� ����� A 5� �U7BD km�Tl sw��e l �(æ_]_fbfZϾ�t[_Y���fZR�MDsxR�Lyfbs\Y\TXNZUXm_`ázÖR�TSgiY\TX`#V*[Fv�R ������������� ��� ����� ����� A 8� �U7 � d�iH�y�ms�e�xgx��æ_]_fZfbÏ°�t[_Y���fbR�MDs\R�Lyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR ����������� ��� ����� ����� A��� �V8 >�km�Tl v ��e l � � �tP�R�T��(�{R�n{]_R�[OUINeV*f��Ov�m_R�MD]_fbNZ[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR � ����� ����� ABA� �V8 �-km�Tl v ��e l ��5��tP�R�TWPw�(�{Rcno]_R�[DUXNQV*f.�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ����� ����� A D� �V8H5 km�Tl v ��e l �o8p�tP�R�TWPw�(�{Rcno]_R�[DUXNQV*f.�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ����� ����� A��� �V8H7 km�Tl v ��e l ��D��tP�R�TWPw�(�{Rcno]_R�[DUXNQV*f.�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ����� ����� D >� �V8B8�d�iH�y�ms�e�xgx����{R�n{]_R�[OUINeV*f.�Ov�mKR�MD]_fbNZ[_säLyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwR ����� ��� ����� ����� D �� �V8 ��km�Tl v ��e l � � �tP�R�T���Ov�mKR�MD]_fbNZ[_s�L�fZs\YxTINbUIm_`ãzÖR�TSgiY\TX`#V*[Fv�R�giY\T u NåéªR�TXR�[DU ~ Y\`a`#V�[FM

W�]_R�]_R��hR�[Ks\UImÐP ��� ��������������������� ��� ��������������������� ��� ����� ����� DB5� �V8HC km�Tl v ��e l ��58�tP�R�TWPw�Û�Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwRagiY\T u NkéhR�TIR�[OU ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� DB7� �V8 A�km�Tl v ��e l �y8³�tP�R�TWPw�Û�Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwRagiY\T u NkéhR�TIR�[OU ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� D�8� �V8HD km�Tl v ��e l ��D8�tP�R�TWPw�Û�Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwRagiY\T u NkéhR�TIR�[OU ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� D �� �V8 � d�iH�y�ms�e�xgx����Ov�m_R�MD]KfZNZ[Ks�LyfZsxY\TXNZUImK`�zÖR�T�giYxTI`#V�[FvwR(giYxT u NkéhR�TIR�[OU ~ Y\`a`#V�[FM�W�]_R�]_R

�hR�[_sxUImFP ������� ��� ��������������������� ��� ��������������������� ��� ����� ����� D A� � �B>�km�Tl sw��e l �(��ë���Ï°ë�VxP�R�M�5XW�� ~ � LyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ��������� ��� ����� ����� �B>� � �D�-km�Tl sw��e l ��5HW ~ �ÖÞ�Þ���� ~ �ó�ª�&R�V*[ � R�P�dFY\[ÐP�R��(Nb`aR�P^O| � Rcno]_RcP�U ~ fQVxPIP ��� ����� �D�� � � 5�d�iH�y�ms�e�xgx����ë��yϾë�V\PSR�M�5XW�� ~ � L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR ������� ��� ����� ����� � 5� � � 7 km�Tl sw��e l �(æ_]_fbfZϾ�t[_Y���fZR�MDsxR�5XW�� ~ � LyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ����� ��� ����� ����� � 7� � � 8�d�iH�y�ms�e�xgx��æ_]_fZfbÏ°�t[_Y���fbR�MDs\R 5HWr� ~ � L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR ��� ��� ����� ����� �\�� � �\��km�Tl v ��e l � � ��P�R�T���5XWó�Ov�m_R�MO]_fZNb[_s�LyfZsxY\TINbUIm_`�z.R�T�giYxTI`#V�[FvwR(giY\T u NåéªR�TXR�[OU ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� � C� � � C km�Tl v ��e l ��5t�tPSR�T�P��Q5HW �ov�m_RcMD]_fZNb[_s�LyfZsxY\TINbUIm_`ãzÖR�T�giY\TX`#V*[ÐvwRgiY\T u NkéhR�TIR�[OU ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� �XA� � �XA�km�Tl v ��e l �H8��tPSR�T�P��Q5HW �ov�m_RcMD]_fZNb[_s�LyfZsxY\TINbUIm_`ãzÖR�T�giY\TX`#V*[ÐvwRgiY\T u NkéhR�TIR�[OU ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� � D

�ONZNbN

Page 11: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� � � D km�Tl v ��e l ��Dt�tPSR�T�P��Q5HW �ov�m_RcMD]_fZNb[_s�LyfZsxY\TINbUIm_`ãzÖR�T�giY\TX`#V*[ÐvwRgiY\T u NkéhR�TIR�[OU ~ Yx`aÏ`#V�[FM�Wy]KR�]_R��hR�[_sxUImFP ������������������� ��� ��������������������� ��� ����� ����� �\�

� � �\� d�iH�y�ms�e�xgx��^5XW �Ov�m_R�MO]_fZNb[_saL�fZs\YxTINbUIm_`áz.R�T�giYxTI`#V�[FvwR���NZUXm u NkéªR�TIR�[OU ~ Y\`a`#V�[FMW�]_R�]_R��hR�[Ks\UImÐP ��� ��������������������� ��� ��������������������� ��� ����� ����� �G>B>

CD� � d�egfhfji\� � � A�� ÿ��h�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR ��� ��� ����� ����� �G> 5CD�U5 kmlon�p e�� � �U5 � ÿ��h�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR � ��� ����� ����� �G> 7CD�U7 q�rtsguwvyxGz���5D� � ÿ��h�{R�n{]_R�[OUINeV*f��Ov�m_R�MD]KfZNZ[Ks�LyfZsxY\TINbUIm_`ÚzÖR�TSgiY\TX`#V*[Fv�R � ��� ����� ����� �G> 8CD�V8 km{ r|uG} k ��5D� � ÿ��F�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`áz.R�T�giYxTI`#V�[FvwR � ��� ����� ����� �G>\�CD� � ~^s���eJs�� � � > ÿ��h�{Rcno]_R�[DUXNQV*f.�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ��� ��� ����� ����� �G> CCD�UC v�e��oiHsg�i� � � > ÿ��F�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`áz.R�T�giYxTI`#V�[FvwR � ��� ����� ����� �G>XACD� A d�egfhfji\� � � A�� ÿ��FLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwRygiY\T u NåéªR�TIR�[DU ~ Yx`a`#V*[ÐM�W�]_R�]KRr�hR�[_s\UXmFP �x�?>CD�UD kmlon�p e�� � �U5 � ÿ��FLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwRygiY\T u NåéªR�TIR�[DU ~ Yx`a`#V*[ÐM�W�]_R�]KRr�hR�[_s\UXmFP �x�?>CD� � q�rtsguwvyxGz���5D� � ÿ��FLyfbs\Y\TXNZUXm_`÷z.R�T�giYxTI`#V�[FvwR�giY\T u NåéªR�TXR�[DU ~ Yx`a`#V�[FM�W�]_R�]_R��hR�[_s\UXmFP �x�\�CD� �?>�km{ r|uG} k ��5D� � ÿ��KLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NkéhR�TIR�[OU ~ Yx`a`#V*[ÐM4W�]_R�]_R��hR�[_sxUImFP �x�\�CD� �\� ~^s���eJs�� � � > ÿ��FLyfbs\YxTINZUXm_`ázÖR�T�giY\TX`#V*[ÐvwR;giYxT u NåéªR�TIR�[DU ~ Y\`a`#V�[FM4W�]_R�]KRr�hR�[_s\UXmFP �x� 5CD� � 5�v�e��oiHsg�i� � � > ÿ��KLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NkéhR�TIR�[OU ~ Yx`a`#V*[ÐM4W�]_R�]_R��hR�[_sxUImFP �x� 5CD� � 7 km�Tl v ��e l �H8��tP�R�TWPw�2�Ov�mKR�MD]_fbNZ[_s�LyfZsxY\TXNZUImK` zÖR�TSgiY\TX`#V*[Fv�R�giY\T u NQPSÎ_P��NZUXm�zTIR�PSR�R�Î

~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ������������������� ��� ��������������������� ��� ����� ����� �x���CD� � 8 km�Tl v ��e l ��8Û��P�R�TWPw���Ov�mKR�MD]_fbNZ[_súLyfbs\YxTINZUXm_` zÖR�T�giY\TX`#V*[ÐvwR giY\T u NeP�ÎKP´��NbUIm�æ_]_fbf

~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ������������������� ��� ��������������������� ��� ����� ����� �x� CCD� ����km�Tl v ��e l ��D��tP�R�TWPw�2�Ov�mKR�MD]_fbNZ[_s�LyfZsxY\TXNZUImK` zÖR�TSgiY\TX`#V*[Fv�R�giY\T u NQPSÎ_P��NZUXm�zTIR�PSR�R�Î

~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ������������������� ��� ��������������������� ��� ����� ����� �x��ACD� � C km�Tl v ��e l �^D¥��P�R�TWPw���Ov�mKR�MD]_fbNZ[_súLyfbs\YxTINZUXm_` zÖR�T�giY\TX`#V*[ÐvwR giY\T u NeP�ÎKP´��NbUIm�æ_]_fbf

~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ������������������� ��� ��������������������� ��� ����� ����� �x� DCD� ��A d�iH�y�ms�e�xgx��r�Ov�mKR�MD]_fbNZ[_s#L�fZs\YxTINbUIm_`ÑzÖR�T�giY\TX`#V*[ÐvwR�giYxT u NeP�ÎKP���NbUIm8zTIR�PSR�R�Î ~ Yx`aÏ

`#V�[FM�Wy]KR�]_R�Nb[_s ��� ��������������������� ��� ��������������������� ��� ����� ����� � 5 >CD� � D�d�iH�y�ms�e�xgx��(�Ov�mKR�MD]_fbNZ[_s�Lyfbs\YxTINZUXm_`ázÖR�T�giY\TX`#V*[ÐvwR;giYxT u NQP�ÎKP���NZUImàæ_]_fZf ~ Y\`a`#V�[FM

W�]_R�]_R�NZ[_s ����� ��� ��������������������� ��� ��������������������� ��� ����� ����� � 5 �CD� ��� d�egfhfji\� � � A�� ÿ��h�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR ��� ��� ����� ����� � 5�8CD�U5 >�kmlon�p e�� � �U5 � ÿ��h�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR � ��� ����� ����� � 5 �CD�U5 � q�rtsguwvyxGz���5D� � ÿ��h�{R�n{]_R�[OUINeV*f��Ov�m_R�MD]KfZNZ[Ks�LyfZsxY\TINbUIm_`ÚzÖR�TSgiY\TX`#V*[Fv�R � ��� ����� ����� � 5BCCD�U5B5 km{ r|uG} k ��5D� � ÿ��F�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`áz.R�T�giYxTI`#V�[FvwR � ��� ����� ����� � 5 ACD�U5B7�~^s���eJs�� � � > ÿ��h�{Rcno]_R�[DUXNQV*f.�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR ��� ��� ����� ����� � 5BDCD�U5�80v�e��oiHsg�i� � � > ÿ��F�{R�n{]_R�[OUINeV*fÖ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`áz.R�T�giYxTI`#V�[FvwR � ��� ����� ����� � 5 �CD�U5 ��km�Tl v ��e l �=D¥�tPSR�T�P���5HW0��ë���Ï°ë�VxP�R�M��Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwR giYxT

u NeP�ÎKP;��NbUIm)zTIR�PSR�R�Î ~ Y\`a`#V�[FM4W�]_R�]KR�NZ[_s � ��������������������� ��� ����� ����� � 7B5CD�U5BC km�Tl v ��e l �=D¥�tPSR�T�P���5HW0��ë���Ï°ë�VxP�R�M��Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwR giYxT

u NeP�ÎKP;��NbUIm)æ_]_fZf ~ Y\`a`#V�[FM4W�]_R�]KR�NZ[_s � ��� ��������������������� ��� ����� ����� � 7B7CD�U5 A�km�Tl v ��e l ��Dt�tPSR�T�P��Q5HW�æ_]_fbfZϾ�t[_Y���fZR�MDsxR��Ov�mKR�MD]_fbNZ[_s�LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwRÖgiYxT

u NeP�ÎKP;��NbUIm)zTIR�PSR�R�Î ~ Y\`a`#V�[FM4W�]_R�]KR�NZ[_s � ��������������������� ��� ����� ����� � 7�8CD�U5BD km�Tl v ��e l ��Dt�tPSR�T�P��Q5HW�æ_]_fbfZϾ�t[_Y���fZR�MDsxR��Ov�mKR�MD]_fbNZ[_s�LyfZsxY\TXNZUImK` z.R�T�giYxTI`#V�[FvwRÖgiYxT

u NeP�ÎKP;��NbUIm)æ_]_fZf ~ Y\`a`#V�[FM4W�]_R�]KR�NZ[_s � ��� ��������������������� ��� ����� ����� � 7 �

NZÔ

Page 12: Aggressive Centralized and Distributed Scheduling ofDisk Requests

CD�U5 � d�iH�y�ms�e�xgx���5XWã��ë���Ï°ë�VxP�R�MÓ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NeP�ÎKP(��NZUImzTIR�PSR�R�Î ~ Yx`a`#V�[FM4W�]_R�]_R�NZ[_s ����������� ��� ��������������������� ��� ����� ����� � 7 A

CD�U7 > d�iH�y�ms�e�xgx���5XWã��ë���Ï°ë�VxP�R�MÓ�ov�m_RcMD]_fZNb[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NeP�ÎKP(��NZUImæ_]_fZf ~ Yx`a`#V�[FM�W�]_R�]_R�NZ[Ks ��������������� ��� ��������������������� ��� ����� ����� � 7BD

CD�U7 � d�iH�y�ms�e�xgx���5XWÚæ_]_fZfbÏ°�t[_Y���fZRcMDs\Ra�Ov�m_R�MO]_fZNb[_s#Lyfbs\Y\TXNZUXm_`ÑzÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NQPSÎ_P��NZUXm)zlTXR�P�R�R�Î ~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ����� ��� ��������������������� ��� ����� ����� � 7 �

CD�U7B5�d�iH�y�ms�e�xgx���5XWÚæ_]_fZfbÏ°�t[_Y���fZRcMDs\Ra�Ov�m_R�MO]_fZNb[_s#Lyfbs\Y\TXNZUXm_`ÑzÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NQPSÎ_P��NZUXm)æÐ]KfZf ~ Y\`p`#V*[FMW�]_R�]_R�NZ[_s ��������� ��� ��������������������� ��� ����� ����� � 8 >

A � � d�egfhfji\� � � A�� ÿ�� u NQPSÎDϾë�V\PSR�M&�_�O��æ¢zÖR�T�giYxTI`#V�[FvwR ������������������� ��� ����� ����� � 8B8A �U5 kmlon�p e�� � �U5 � ÿ�� u NQPSÎDϾë�V\PSR�M&�_�O��æ¢zÖR�T�giYxTI`#V�[FvwR ����������������� ��� ����� ����� � 8 �A �U7 q�rtsguwvyxGz���5D� � ÿ�� u NeP�ÎOÏ°ë�VxP�R�M&�_�O��æÛzÖR�T�giY\TX`#V*[ÐvwR ����������������� ��� ����� ����� � 8HCA �V8 km{ r|uG} k ��5D� � ÿ�� u NQPSÎDϾë�V\PSR�M��K�O��æÛzÖR�T�giYxTI`#V�[FvwR ����������������� ��� ����� ����� � 8 AA � � ~^s���eJs � � > ÿ�� u NQP�ÎOϾë�V\P�RcMà�K�O��æÛzÖR�T�giYxTI`#V�[FvwR ������������������� ��� ����� ����� � 8HDA �UC v�e��oiHsg�i� � � > ÿ�� u NQPSÎDϾë�V\PSR�M��K�O��æÛzÖR�T�giYxTI`#V�[FvwR ����������������� ��� ����� ����� � 8 �A � A kmlon�p e�� � �U5 � ÿ�� u NQPSÎDϾë�V\PSR�M&�_�O��æ¢zÖR�T�giYxTI`#V�[FvwR ����������������� ��� ����� ����� ���B>A �UD d�egfhfji\� � � A�� ÿ�� u NQPSÎDϾë�V\PSR�M&�Oz ~ ��æßzÖR�T�giY\TX`#V*[ÐvwR ��������������� ��� ����� ����� ���D�A � � kmlon�p e�� � �U5 � ÿ�� u NQPSÎDϾë�V\PSR�M&�Oz ~ ��æßzÖR�T�giY\TX`#V*[ÐvwR ��������������� ��� ����� ����� ��� 5A � �?> q�rtsguwvyxGz���5D� � ÿ�� u NeP�ÎOÏ°ë�VxP�R�M&�Oz ~ ��æßz.R�T�giYxTI`#V�[FvwR ��������������� ��� ����� ����� ��� 7A � �\�-km{ r|uG} k ��5D� � ÿ�� u NQPSÎDϾë�V\PSR�M��oz ~ ��æÛzÖR�T�giY\TX`#V*[ÐvwR ��������������� ��� ����� ����� ��� 8A � � 5�~^s���eJs�� � � > ÿ�� u NeP�ÎOÏ°ë�VxP�R�M&�Oz ~ ��æ¢zÖR�T�giYxTI`#V�[FvwR ����������������� ��� ����� ����� ���\�A � � 7�v�e��oiHsg�i� � � > ÿ�� u NQPSÎDϾë�V\PSR�M��oz ~ ��æÛzÖR�T�giY\TX`#V*[ÐvwR ��������������� ��� ����� ����� ��� CA � � 8 kmlon�p e�� � �U5 � ÿ�� u NQPSÎDϾë�V\PSR�M&�Oz ~ ��æßzÖR�T�giY\TX`#V*[ÐvwR ��������������� ��� ����� ����� ���XAA � ��� d�egfhfji\� � � A�� ÿ�� u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR � ��� ����� ����� ���\�A � � C kmlon�p e�� � �U5 � ÿ�� u NQPSUITXNZ^_]_UXR�MÓ�Ov�m_R�MO]_fZNb[_s�LyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR � ��� ����� ����� � C >A � ��A q�rtsguwvyxGz���5D� � ÿ�� u NeP�UITXNZ^_]KUIR�MÓ�ov�m_RcMD]_fZNb[_s�Lyfbs\Y\TXNZUXm_`÷z.R�T�giYxTI`#V�[FvwR ��� ����� ����� � C �A � � D km{ r|uG} k ��5D� � ÿ�� u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR � ��� ����� ����� � CB5A � ��� ~^s���eJs�� � � > ÿ�� u NeP�UXTINZ^K]_UIR�M&�Ov�m_R�MO]_fZNb[_s�Lyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR � ��� ����� ����� � CB7A �U5 > v�e��oiHsg�i� � � > ÿ�� u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR � ��� ����� ����� � C�8A �U5 �-kmlon�p e�� � �U5 � ÿ�� u NQPSUITXNZ^_]_UXR�MÓ�Ov�m_R�MO]_fZNb[_s�LyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR � ��� ����� ����� � C �A �U5B5 km�Tl v ��e l �mDa�tP�R�T�Pw� u NeP�UITXNZ^_]KUIR�M��Ov�mKR�MD]_fbNZ[_s�Lyfbs\YxTINZUXm_`ázÖR�T�giY\TX`#V*[ÐvwRygiY\T u NQPSÎ_P

��NZUXm)zlTXR�P�R�R�Î ~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ����� ��� ��������������������� ��� ����� ����� ��A�>A �U5B7 km�Tl v ��e l �mDa�tP�R�T�Pw� u NeP�UITXNZ^_]KUIR�M��Ov�mKR�MD]_fbNZ[_s�Lyfbs\YxTINZUXm_`ázÖR�T�giY\TX`#V*[ÐvwRygiY\T u NQPSÎ_P

��NZUXm)æÐ]KfZf ~ Y\`p`#V*[FMW�]_R�]_R�NZ[_s ��������� ��� ��������������������� ��� ����� ����� ��A{�A �U5�8�d�iH�y�ms�e�xgx�� u NQP�UXTINb^_]_UIRcMä�ov�m_RcMD]_fZNb[_s�LyfZsxY\TINbUIm_` zÖR�T�giYxTI`#V�[FvwRgiY\T u NQPSÎ_P���NZUXm�zlTXR�Ï

P�R�R�Î ~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ��������������� ��� ��������������������� ��� ����� ����� ��A 5A �U5 � d�iH�y�ms�e�xgx�� u NQP�UXTINb^_]_UIRcM �Ov�mKR�MD]_fbNZ[_s�L�fZs\YxTINbUIm_`ãzÖR�TSgiY\TX`#V*[Fv�R�giY\T u NeP�ÎKPÖ��NZUXmaæ_]_fbf

~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s ������������������� ��� ��������������������� ��� ����� ����� ��A 7A �U5BC�d�egfhfji\� � � A�� ÿ�� u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR � ��� ����� ����� ��ABAA �U5 A�kmlon�p e�� � �U5 � ÿ�� u NQPSUITXNZ^_]_UXR�MÓ�Ov�m_R�MO]_fZNb[_s�LyfZsxY\TXNZUImK`÷zÖR�T�giY\TX`#V*[ÐvwR � ��� ����� ����� ��A DA �U5BD�q�rtsguwvyxGz���5D� � ÿ�� u NeP�UITXNZ^_]KUIR�MÓ�ov�m_RcMD]_fZNb[_s�Lyfbs\Y\TXNZUXm_`÷z.R�T�giYxTI`#V�[FvwR ��� ����� ����� ��A��A �U5 ��km{ r|uG} k ��5D� � ÿ�� u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR � ��� ����� ����� � D >A �U7 > ~^s���eJs�� � � > ÿ�� u NeP�UXTINZ^K]_UIR�M&�Ov�m_R�MO]_fZNb[_s�Lyfbs\YxTINZUXm_`ÚzÖR�T�giYxTI`#V�[FvwR � ��� ����� ����� � D �

Ô

Page 13: Aggressive Centralized and Distributed Scheduling ofDisk Requests

A �U7 � v�e��oiHsg�i� � � > ÿ�� u NQPSUITXNZ^_]_UXR�M&�Ov�m_R�MD]_fbNZ[_säLyfZsxY\TXNZUImK`ázÖR�TSgiY\TI`ÕV*[FvwR � ��� ����� ����� � DB5A �U7B5 km�Tl v ��e l ��D8�tP�R�TWPw� u NeP�UITXNZ^_]KUIR�M�5XWÑ�Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` zÖR�TSgiY\TI`ÕV*[FvwRagiYxT

u NeP�ÎKP;��NbUIm)zTIR�PSR�R�Î ~ Y\`a`#V�[FM4W�]_R�]KR�NZ[_s � ��������������������� ��� ����� ����� � DBCA �U7B7 km�Tl v ��e l ��D8�tP�R�TWPw� u NeP�UITXNZ^_]KUIR�M�5XWÑ�Ov�mKR�MD]_fbNZ[_s8LyfZsxY\TXNZUImK` zÖR�TSgiY\TI`ÕV*[FvwRagiYxT

u NeP�ÎKP;��NbUIm)æ_]_fZf ~ Y\`a`#V�[FM4W�]_R�]KR�NZ[_s � ��� ��������������������� ��� ����� ����� � D AA �U7�8�d�iH�y�ms�e�xgx�� u NeP�UITXNZ^_]KUIR�M�5XWã�Ov�m_R�MD]_fbNZ[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NeP�ÎKP(��NZUIm

zTIR�PSR�R�Î ~ Yx`a`#V�[FM4W�]_R�]_R�NZ[_s ����������� ��� ��������������������� ��� ����� ����� � DBDA �U7 � d�iH�y�ms�e�xgx�� u NeP�UITXNZ^_]KUIR�M�5XWã�Ov�m_R�MD]_fbNZ[_s�L�fZs\YxTINbUIm_`ÚzÖR�TSgiY\TI`ÕV*[FvwR�giY\T u NeP�ÎKP(��NZUIm

æ_]_fZf ~ Yx`a`#V�[FM�W�]_R�]_R�NZ[Ks ��������������� ��� ��������������������� ��� ����� ����� � D �Lr� � ×tz ~ 5B5�8 A u NeP�Î u TXNZ�{R��{R�R�Î ~ ]_TX�{R ����� ��� ��������������������� ��� ����� ����� 5 >B>Lr�650ýBV*fbNQM_V�UINZYx[ � R�PSdFY\[FPSR��(NZ`pR u NeP�UXTINZ^K]_UINbY\[FP�� �x�X� � V*[FMOY\` � RcV\M_P ��� ����� ����� 5 > 5Lr�670ýBV*fbNQM_V�UINZYx[ � R�PSdFY\[FPSR��(NZ`pR u NeP�UXTINZ^K]_UINbY\[FP�� �x�X� � V*[FMOY\`á�"TXNZUXR�P ��� ����� ����� 5 > 5Lr�98ÑýBV*fbNQM_V�UINZYx[ � R�PSdFY\[FPSR��(NZ`pR u NeP�UXTINZ^K]_UINbY\[FP�� �x�X� �{Rcno]_R�[DUXNQV*f � RcV\M_P � ����� ����� 5 > 7Lr� � ýBV*fbNQM_V�UINZYx[ � R�PSdFY\[FPSR��(NZ`pR u NeP�UXTINZ^K]_UINbY\[FP�� �x�X� �{Rcno]_R�[DUXNQV*fª�"TXNZUXR�P � ����� ����� 5 > 7

ÔON

Page 14: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��� ��� ö ñ>/ �

M���� + ��!�%B�� + �

�,�?� î ���t�2�à����u NQPSÎ#P�]K^FP�|KP�UXR�`#P�`�]FPSU�^FR�RwéªR�vwUXNZ�{R�fb|r]_UXNZfbNZÙ�R�M�UIY�v�Y\`adFR�[FPXV*UXR;giYxT�UIm_R�s\TXY���NZ[_s�dFR�TSgiY\TI`ÕV*[FvwR

MDNeP�dFV�TINZUS|Û^FR�US�(R�R�[òdKTIYOvwR�PXP�Nb[_s¢V*[FM�PSUIY\TWV*sxRúvwY\`adFYx[_R�[OU�Pw� u NeP�΢�(Y\TXÎDfbY{VxM_PaV*TXR&Y�giUIR�[§v�mFV*TWV\vwÏUIR�TINZÙ�R�Mò^O|ÛNZ[OUIR�[FPSR&^_]KT�P�UWP Y*gäVxvwUINb�DNbU�|���vwTIRcV*UINb[_súfZY\[Ksßn{]_R�]KR�P´Y�g�d5R�[FMDNZ[KsòTXR�n{]_R�P�UWP��â��v��y]�DTC{�� ]_R�` � 7E ¾�t��m_R�[úPS]Fv�mún{]_R�]KR�PtMDR��{R�fZY\d±�5UXm_R�MDNQPSÎ)PIv�m_R�MD]_fbR�T�MD|D[ÐV*`aNev�V*fbfZ|aTXR�Y\TWMDR�T�P�d5R�[FMDNZ[KsaTIR�Ïn{]_R�P�UWPqUXY�MDR�v�TIR�VxP�RBP�R�TX�DNevwR2UINb`aR�Pw�±LòPSNZsx[_Nåjªv�V*[OUÖdFY\TXUINbY\[�Y*g5MDNQPSÎrPSR�TI�ONQv�R�UXNZ`aRlvwY\[FPSNQPSU�P�Y*gª`aR�v�mFV*[KÏNQv�V*f_dFY{PSNZUXNZY\[KNZ[_säMDR�fQV�|KPw�{��m_Nev�m�V�TIR�m_NZsxm_fZ|�MDR�d5R�[FMDR�[OU2Y\[�UIm_R�TIR�feV*UXNZ�{R(dFY�P�NZUXNZYx[FP�Y�g.UIm_R�TIR�n{]_R�PSUIR�M^_fbYOv�ÎKP�V*[FM#UIm_Rävw]_TXTIR�[OU(TXR�V\M5Ý���TINbUIRrmKR�V\MadFY{PSNZUINbY\[���ë(|aU�V�ÎDNb[_s Nb[DUXY�V\v�v�Y\]_[OU�UIm_R��xV*TXNZYx]FPtMDR�feV�|_PV\PXP�YOvwNeV*UXR�M¥��NZUIm³MDNQPSÎ¥Vxv�vwR�PXP�R�P��V�PIv�m_R�MO]_fZR�T�v�V�[¥d_TXYOMD]FvwR)VÓTXR�n{]_R�P�UäP�R�n{]_R�[ÐvwR UXmFV*U�`aNZ[KNZ`aNkÙ�R�PUImKR�`pR�V*[#dFY{PSNZUINbY\[_Nb[_s�UINZ`pRy��m_NbfZR�d_TXY*�ONQMONZ[_s�R�n{]_NbU�V*^KfZRtTXR�P�dFY\[ÐP�RrUXNZ`aRcPlgiY\T�NZ[ÐMDNZ�ONQMD]ÐV*fhTXR�n{]_R�P�UWPw�Ü°[&`#V�[D|Õv�V\PSR�Pw�F^FR�UIUXR�TyY��{R�TWV*fbf.P�|KP�UIR�`÷dFR�T�giYxTI`#V�[FvwR�v�V*[�^FRäV\v�m_NZR��{RcM ^D|)VaMONQP�Î)PXv�m_RcMD]_fZR�T�UImFV�Ud_TXNZY\TXNZUXNZÙ�R�PTXR�no]KR�P�UWPl^ÐV\P�RcMÕYx[#UIm_R�NbT�:INZ`pd5YxTIUWV*[FvwRE<�UIY�UIm_R�P�|KP�UIR�`÷VxP(Vr��m_YxfZR{�2L§PIv�m_R�MD]KfZR�T2��NZUXmV\v�vwR�PIP�UIYpV*dKd_fZNev�V*UXNZY\[KÏØfbR��{R�fhYxTtPS|_PSUIR�`pÏØfbR��{R�fFNZ[DgiYxTI`#V�UINbY\[)v�V*[)s\R�[KR�T�V�UIR�V�TIRcno]_RcP�U�PIv�m_R�MD]_fbR�UImFV�Ud_TXYOMD]FvwR�P�`aYxTIRt[_RcV*TIfb| Yxd_UINb`#V*f±P�|KP�UXR�`÷dFR�T�giYxTI`#V�[FvwR{�

�qTWV\MDNbUINbY\[FV�f(MONQP�ÎàPIv�m_R�MD]KfZR�TWPyUS|Dd_Nev�V*fbfZ|a]KUINZfbNZÙ�RäP�Nb`ad_fZR�V�fZs\YxTINbUIm_`#P�UImFV�U�TXR�n{]_NZTXRrfZNbUIUXfZRrÎO[_Y���fZÏR�MDsxR#Y*g�P�|KP�UIR�` sxY{V*feP´YxT�UIm_RÕP�U�V�UIR#Y*g�UImKR&MONQP�Î8P�]K^FP�|KP�UXR�`��ú�(m_R#NZ[Fv�TIR�VxP�NZ[Ks�V*`pY\]_[OUrY�g�vwYx`aÏd_]_UWV*UXNZY\[)V�[FMÓ`aR�` YxTI|rTXR�P�Yx]_T�v�R�P�V��\V�NZfeV*^_fbRygiY\T�PXv�m_RcMD]_fZNb[_s�VxvwUINb�DNbUINbR�P`#V*Î{R�P`aYxTIR�P�Yxd_m_NQPSUINev�V*UXR�MMDNeP�ÎÛPXv�m_RcMD]_fZNb[_súV*fbs\YxTINZUXm_`#P�giR�VxP�Nb^_fZR{�¢LtP�UIm_R)MDR�`#V*[FMKPrY\[§ÜIÝ\Þ P�]_^FPS|_PSUIR�`ÕPrNZ[FvwTXR�V\PSR{�gi]_UI]_TXRm_Nbs\m_ÏidFR�T�giYxTI`#V�[FvwR#PS|_PSUIR�`#Pt��NbfZf2TIR�n{]_NbTIRa`aYxTIR�RwÒÕvwNZR�[OU�V�[FM¥RwéªR�vwUINb�{RaMONQP�Î8V\v�vwR�PIP��úLys\sxTIR�PXP�NZ�{RMDNeP�ÎaTXR�no]KR�P�U�PXv�m_RcMD]_fZNb[_sr��NbfZfªd_fQV�|#Vr`#V�ùSY\T�TIYxfZRtNb[)V\v�m_NZR��ONZ[KsrUImKNQP�s\Y{V�f°�

u NQPSÎaPXv�mKR�MD]_fbR�T�PBv�V*[a^FRygiYx]_[FMaNZ[ÕV*d_d_fbNQv�V�UINbY\[ad_TXY\sxT�V*`ÕP } R{�âs_�Z�OM_V�U�V�^FV\PSRrPSUIYxT�V*sxRr`#V�[FV*sxR�T�P����Þ�Ý\�ÕMDR��ONQvwR�MDTINb�{R�T�P��DNb[DUXR�TI`aRcMDNQV�UIR�ÜIÝ\Þ vwY\[OUITXY\fZfbR�T�P } R{�âs_�b�_MDNeP�Î#V�TIT�V�|#v�Y\[OUITIYxfZfbR�T�P����_V�[FMÓYx[_Ïi^5Y�V*TWMMDNeP�Î�MOTINZ�{R�v�Y\[OUITIYxfZfbR�T�P��ÖÜ°[�`aY{PSU2P�|KP�UXR�`#P��*m_Y��BR��{R�T���V�MONQP�Î�TIR�n{]_R�PSUR�[Fv�Y\]_[OUIR�TWPÖY\[KfZ|�Y\[KR�:WV\vwUXNZ�{R�<PIv�m_R�MO]_fZR�T�Nb[#UIm_R�dFV*UXmÓgiTIYx`áUIm_R�V*dKd_fZNev�V*UXNZY\[)d_TIYxs\TWV*`øUXY UXm_R�MDNQPSÎ)MDTINb�{Rt`aR�MDNeVD��Þ�[_R�V*d_d_TXY{Vxv�mUIY)NZ`adKTIY��DNb[_s�d5R�T�giY\TX`#V*[ÐvwR�NQPtUIY#Nb[FvwTIRcV\P�R�UImKRaV�`aY\]_[OUtY�g�NZ[OgiY\TI`ÕV*UINbY\[8V��\V�NZfeV*^_fbR�UIY#UIm_RpV\v�UINZ�{RPIv�m_R�MO]_fZR�TlV*[FM#V*]Ks\`aR�[OUR�ÔONQPSUINb[_s�PIv�m_R�MD]_fbNZ[_s�V�fZs\YxTINbUIm_`#PUXYrU�V�Î{RyUXm_NQP2NZ[DgiYxTI`#V�UINbY\[�NZ[OUIYäV\v�v�Y\]_[OU��

�ÖéhRcvwUINb�{R¢¡HR�£�¤ b�O P ]S¥ R�¦¨§?¡�©QR�¦ ` P ] £ _ TXR�no]KNZTIRcP UImFV�U#]FP�Rwgi]Kf�Nb[DgiY\TX`#V*UXNZYx[�^5RúNQMOR�[DUXNåjFRcMh��R�ÔDÏUITWV\vwUXR�Mh�ªV*[FM#UITWV*[FPS`aNZUXUIR�M#V*fbY\[_spUIm_RäÜWÝxÞódFV*UXm�UIYpVaP�Nb[_s\fbR�VxvwUINb�{R�PIv�m_R�MD]KfZR�T���zÖY\dK]_fQV�TtNZ[OUIR�TX`aR�ÏMDNeV*UIR�V�[FMÓdFR�TXNZd_m_R�T�V*f�^K]FP;dKTIY\UXYOvwY\fePtMDY�[_Y\U�g¾V\v�NZfZNbU�V�UIRtUXm_R�UIT�V�[FP giR�TyY�gBP�]Fv�m)vwY\[OUITXY\f�Nb[DgiY\TX`#V*UXNZY\[} R�� s_�b�hTIRcP�Y\]KT�vwR�PSU�V*UX]FP�Ý�]_UINbfZNbÙ�V*UXNZY\[8V*[ÐM�TXR�no]KR�P�UtdKTINZYxTINbU�|��hMDR�d5R�[FMDR�[Fv�|{��V*[ÐM"V�s\NZ[Ks&NZ[OgiY\TI`ÕV*UINbY\[h�W�

Page 15: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5

LyfeP�Y_�B[_Y\U#V�fZf(jFfbR�PS|_PSUIR�` V*[ÐM�MDR��ONQvwR#MOTINZ�{R�T�NZ[OUIR�TSg¾V\vwR�PrmÐVc�{R)UIm_R�ªFR�ÔONZ^_NbfZNbU�|�UXYÛvwYx`a` ]K[_Nbv�V*UXRdFR�TIUXNZ[_R�[DU�PIv�m_R�MD]_fbNZ[_s�Nb[DgiY\TX`#V*UXNZYx[��

ÜSMDR�V*fbfZ|{�OUIm_R�fZYOv�V�UINbY\[&Y�gBV�vwR�[OUIT�V�fZNbÙ�R�MaPXv�m_RcMD]_fZR�T�P�mKY\]_feMÓ^FR�v�m_Y{PSR�[&UXY `pNZ[_Nb` NbÙwR�UIm_R�vwYx[DUXTIYxfNZ[OgiY\TI`ÕV*UINbY\[�UXT�VcÒÕv���m_NZfbR�V\PIPS]_TINb[_s&UXNZ`aR�fZ|#Vxv�vwR�PXP�UXY#UIm_R�`aY{PSUt]FPSRwgi]_f2vwYx[DUXTIYxf�Nb[DgiY\TX`#V*UXNZYx[���Ü°[V\MKMDNZUXNZY\[±�DV�PIv�m_R�MD]KfZR�T2PSm_Y\]KfQM mFV��{R�PS]DÒ#v�NZR�[OU2vwYx`ad_]_UWV*UINbY\[pV*[FM�`aR�`aYxTI|tTXR�P�Yx]_T�vwRcPlUXYrRwÒÕvwNbR�[DUXfZ|d_TXYOvwR�PIP2NZ[Fv�Y\`aNb[_s�NZ[DgiYxTI`#V�UINZYx[��\`#V�NZ[OU�V�NZ[pno]_R�]_R�PY*g.dFR�[FMONZ[_s�TIR�n{]_R�PSU�Pw�KV*[FM�d5R�T�giY\TX`÷PXv�mKR�MD]_fbNZ[_sV\v�UINZ�ONZUXNZR�P } N°� R��Z�OP�R�V�T�v�m_NZ[Ks�V*[FM)P�Y\TXUINb[_s�UIm_R�dFR�[FMONZ[_s�TXR�no]KR�P�U�n{]_R�]_RcP������(m_R�vwY{PSUtV�[FM#vwY\`pd_fZR�ÔONZUS|MDNePIV\MO�\V�[DUWV*sxR�PyY*glvwR�[OUITWV*fbNZÙ�R�M�PIv�m_R�MO]_fZNb[_s_�Om_Y��(R��{R�T��D`aYxUINb�\V�UIR�M�UIm_R�NZ[O�{R�PSUINZs�V*UXNZY\[pY*gBV�[�V*fbUIR�TX[FV*ÏUINb�{R�PIv�m_R�MO]_fZNb[_srdFV�T�VxMDNZsx`��

��] §«¤ b�] 3 ` ¤�R�¦�§G¡�©cR�¦ ` P ] £ _ dÐV*TIUXNZUXNZY\[ÐPÓUImKR¥[_R�vwRcPIPIV�TI| V\vwUXNZ�ONZUXNZR�PaV�`aY\[Ks�P�R�dFV*TWV*UIRÛR�[OUINbUINbR�PV*fbY\[_spUIm_R�ÜIÝ\ÞódÐV*UIm±�t�(m_R�PXv�m_RcMD]_fZNb[_s�R�[OUINbUINZRcP(` ]FPSU�vwY{Y\dFR�TWV*UXR } N°� R��Z�DR�Ô_v�mFV*[Ks\R�VxM_MDNbUINZYx[FV*flvwY\[_ÏUITXY\f.NZ[DgiYxTI`#V�UINbY\[h�2Nb[&Y\TWMDR�T�UIYadKTIR��{R�[OU�]_[FMOR�P�NbT�V*^KfZR�NZ[OUIR�TWV\vwUXNZYx[FPw��Ltv�m_NZR��DNb[_s�PS]Fv�màvwY{Y\TWMDNZ[ÐV*UINbY\[`#V�|&TXR�n{]_NZTXR�v�mFV�[_s\RcP�UXY&R�ÔONQPSUINb[_s�Þ�Ýx�&Nb[DUXR�T�g¾VxvwR�PtV�[FM"^_]ÐP�d_TXY\UIYOv�Y\fQP��&��{R�[���NbUIm8V*d_dKTIY\dKTINQV�UIRmFV�T�MD��V*TIRàV*[FM�PSY*giUS��V�TIR)`aYOMDNåj5v�V*UXNZY\[ÐPw�BMDNQPSUITINb^_]_UXR�MÛPIv�m_R�MD]_fbNZ[_s�`ÕVc|8[_Y\UpV*UXU�V*Nb[ßdFR�TSgiY\TI`ÕV*[FvwRR�n{]_NZ�xV�fZR�[OU UXYÛUImFV�UÓY�g¬:IY\`p[_NQPXvwNZR�[OUg<úvwR�[OUITWV*fbNZÙ�R�M¢PIv�m_R�MD]KfZNZ[Ks } N°� R��Z��PXv�m_RcMD]_fZNb[_s¥��NbUIm§vwYx`ad_fZR�UIRÎO[_Y���fZR�MDsxR&Y�g�V*fbfy]FPSRwgi]_f�NZ[DgiYxTI`#V�UINbY\[¢vwY\]Kd_fZR�MÛ��NZUXm�P�]OÒ#vwNbR�[OU�TIR�PSY\]_TWvwR�P�UIYúRwéªR�vwUINb�{R�fZ|ú]_UXNZfZNbÙ�RUImKRaNZ[DgiYxTI`#V�UINbY\[h�W�#æÐYxTrTXR�V*fbNQP�UXNQvrNb`ad_fZR�` R�[OUXV*UXNZY\[ÐPw�hm_Y��BR��{R�T��.MDNeP�UXTINZ^K]_UIR�M8PIv�m_R�MD]_fbNZ[_s#mFVxPrvwY�P�U��vwYx`ad_fZR�ÔDNbU�|��\V�[FMÓdFR�TSgiY\TI`ÕV*[FvwR�V\MD�xV*[OU�V�s\R�P��

Þ��{R�T�UIm_RBdFV\PSU�5 � |{R�V*TWPw�xVy�xV*TINbR�US|tY*g5PIv�m_R�MD]_fbNZ[_s�V�fZsxY\TINbUIm_`ÕPqmFV��{R2^FR�R�[�d_TIYxd5Y�P�R�M�V*[ÐMrP�UX]FMDNbR�MNZ[ú^FY\UXmÛV\v�VxMDR�`aNeVaV*[ÐM�Nb[FMD]FPSUITI|��azTIR��ONZYx]FP�PIv�m_R�MD]KfZNZ[Ks#V*fbs\Y\TXNZUXm_`ÑP�UX]FMDNZRcP�US|Od_NQv�V*fZfb|#]FP�R�MúP�Nb`aÏd_fbNQP�UXNQv�MDNeP�Î#`aYOMDR�feP(fQVxv�ÎONZ[_s�PSR��{R�TWV*f�NZ`pd5YxTIUWV*[OU;giR�V�UI]_TXR�P�Y*g2`aYOMOR�TI[àMDNQPSÎ&MOTINZ�{RcP } R{�âs_�Z�_Yx[_Ïi^5Y�V*TWMv�Vxv�m_RcP������(m_R�^FR�[Fv�m_`#V�TIÎa�BY\TXÎDfbY{V\MKP��BR�TIR�]ÐP�]FV�fZfZ|àP�|O[DUXm_R�UXNQv\�F]FP�Nb[_s#PSNZ`ad_fbR�d_TIYx^FV*^_NbfZNbU�|)MDNeP�UXTINZÏ^_]_UXNZYx[FP } R�� s_�b�_]_[_NkgiY\TI`à�D]_[_Nb`aYOM_V�f°�FY\T�^_NZ`aYOMKV*fØ�2giY\T�TIRcno]_RcP�U�P�U�V�TIUXNZ[_safbYOv�V*UXNZYx[FPw��×yY{PSU;giR�RcMD^FV\v�ÎRwéªR�vwUWP´�BR�TIR)NZsx[_Y\TXR�M } R{� sK�Z�2Y\dFR�[§P�]K^FP�|KP�UXR�` `aYOMDR�feP´��NbUImßR�ÔDdFY\[KR�[DUXNQV�fZfZ|³MDNQPSUITINb^_]_UXR�MòTXR�no]KR�P�UNZ[OUIR�T�V*TXTINb�\V�fUINb`aR�P��2Y\TrY��{R�TWP�Nb`ad_fZNèjFRcM } R{� sK�Z�ªvwfZY�P�R�MúP�]K^FP�|KP�UXR�`ø`aYOMOR�fQPy`ÕV*NZ[OU�V�NZ[_Nb[_spV&vwYx[FP�UWV*[OU[O]_` ^FR�T�Y*g�Yx]_U�PSU�V*[ÐMDNZ[_s¢TIR�n{]_R�PSU�P����ã�(m_R¥v�Y\[Fvwfb]FP�NbY\[FP�UIm_R�TXRwgiY\TXRúP�m_Yx]_fQM�^FR¥v�Y\[FPSNQMDR�TXR�MòNb[¼V�[V*dKd_TIYxd_TINeV*UIR�vwY\[OUIR�ÔOU��.�&Y�P�U�V�d_d_fb|�Y\[_fb|rUIYäV�P�`#V�fZfFPSR�UY*g.�BY\TXÎDfbY{V\MKPw�{��m_NQv�mpV*TIR�US|DdKNQv�V�fZfZ|�]_[KTIR�d_ÏTIRcP�R�[OU�V�UINZ�{R�Y*g2TXR�V*fbÏØ�BY\TIfeM&PS|_PSUIR�`#P��_PSR�TI�ONQvwRcMÕ^O|aYx]_U�M_V�UIR�M)MDNQPSÎ)MDTINb�{R�vwY\`pd5Yx[_R�[OU�P���Ü°[&v�Y\[OUIT�VxP�U��UImKR#P�UX]FMDNZRcPrMDNePIvw]FPXP�R�MúNZ[¥UXm_NQP�MDNQPXP�R�TXU�V*UXNZYx[ò]ÐP�R#V�PSNZ`�]_fQV�UIY\T�vwY\[OU�V�NZ[_Nb[_súVÓ�{R�TX|úMDR�UWV*NZfbR�Mh�.�(R�fbfZÏ�xV*fbNQM_V�UIR�M�MDNeP�Î�`aYOMDR�f¾�Ö�(mKRtPSNZ`�]_fQV�UIY\T.]FPSR�PUIT�VxvwR�PÖUWV*Î{R�[rgiTXY\`�PS|_PSUIR�`#P.V*UBPSR��{R�T�V�fDNb[FMD]FPSUITXNQV*fÐV*[FMTIRcP�R�V�T�v�mÓNb[FP�UWV*fbfQV*UXNZYx[FPw���{Y\`pR�Y�gUXm_RrR�ÔDdFR�TXNZ`aR�[OU�P]FPSR�V*[&YxdFR�[úP�]_^ÐP�|KP�UIR�`÷`aYOMDR�f¾�D��m_NbfZR�Y\UXm_R�TWP]FPSR�V�TXR�V*fbNQPSUINQv2m_Y{PSU2`aYOMDR�fKMDR��{R�fbY\dFR�M�V*U2UIm_R���[_NZ�{R�TWP�NbU�|�Y*g±�&NQv�m_NZs�V*[¬�èûtV�[_s � 7B °���(m_R�m_Y{PSU2`aYOMDR�fd_TXY*�ONQMOR�P�P�|KP�UIR�`0d5R�T�giY\TX`#V*[ÐvwR�`aR�UXTINQv�P;UXYÓ`pR�V\PS]_TIR�UXm_R ]ÐP�R�TXÏØfbR��{R�fNb`adFV\v�UyY�g�PIv�m_R�MD]_fbR�T�MDRcP�NZsx[v�m_Y\NevwR�Pw�

�,�g­ ö�')����� $a��������® �����zTIR��ONZYx]FP�P�UI]ÐMDNZR�PtY�g�MDNeP�ÎúPIv�m_R�MO]_fZNb[_s#V*fbs\YxTINZUXm_`#PtV�TIR�NZ[FVxMDR�n{]FV*UXR´giYxT�vwY\`adK]_UIR�T�P�|KP�UXR�`0R�[_Ï

s\Nb[_R�R�TWP�vwY\[ÐvwR�TI[KR�M¼��NZUImóYxd_UINb`aNZÙ�Nb[_s¢MDNQPSÎóP�]K^FP�|KP�UXR�` dFR�T�giYxTI`#V�[FvwR{� �(m_NQPúMDNePIP�R�TIU�V�UINbY\[ód_TIYxÏ�ONQMDR�P�s\]KNQMDR�fbNZ[_RcP�giYxTtMDRcP�NZsx[_NZ[Ks#V*[FM&Nb`ad_fbR�`aR�[DUXNZ[_säV*s\sxTIR�PXP�Nb�{R�MDNeP�Î&TXR�n{]_R�P�U�PIv�m_R�MO]_fZR�TWP(NZ[�m_Nbs\m_ÏdFR�T�giYxTI`#V�[FvwR�PS|_PSUIR�`ÕP�R�n{]_NZdKd5RcMÕ��NbUIm)P�UWV*UXR�ÏØY�giÏØUXm_R�ϾV*TXUtPSUIY\TWV*sxR�vwY\`adFYx[_R�[OU�Pw�

Page 16: Aggressive Centralized and Distributed Scheduling ofDisk Requests

7

�,�°¯ �Ñ%�% + ® ±"����'�® ��� �2� +�, �2'���Ú� ���.�t������2 + �

² Ü°U.NQP.P�m_Y���[�UImÐV*U2MDNeP�UXTINZ^K]_UIR�M�PIv�m_R�MD]KfZR�T�Nb`ad_fZR�` R�[OU�V�UINbY\[FPFd_TIY��ONQMDRBd5R�T�giY\TX`#V*[ÐvwR2R�no]ÐV*fOUIYtYxTPS]_dFR�TINbY\T.UIY�UImFV�UY*gFRcno]_Nb�xV*fZR�[DU±vwR�[OUIT�V�fZNbÙ�R�MtPXv�m_RcMD]_fZR�ThNZ`pd_fZR�`�R�[OU�V�UINZYx[FPDgiY\T.`aY{PSU��(YxTIÎOfZY{VxM_PPSUI]FMDNbR�Mh��{Nb[FvwRBMDNQPSUITXNZ^_]_UXR�M�PIv�m_R�MD]KfZNZ[Ks�V*fQPSYymÐV\P.vwY{PSUV�[FM�vwY\`pd_fZR�ÔONZUS|�V\MD�xV*[OU�V�s\R�P��\UImKNQP�[_R��PXv�m_RcMD]_fZNb[_srdÐV*T�VxMDNZsx`áNQP(TIRcvwY\`a`pR�[FMDR�M�giYxT;gi]KUI]_TXR�mKNZs\mKÏØdFR�TSgiY\TI`ÕV*[FvwR�P�|KP�UIR�`#Pw�

² Ü°U�NQPtPSm_Y���[�UImFV�U�V*fbs\Y\TXNZUXm_`#P�NZ[FvwYxTIdFY\TWV*UXNZ[_s)P�|KP�UXR�`aÏifZR��{R�f5Nb[DgiY\TX`#V*UXNZYx[ } R�� s_�b�FMDNQPSÎ&TXR�no]KR�P�Ud_TXNZYxTINZUXNZR�P��(dKTIY��DNeMDR�UImKR�m_NZsxm_R�P�U�fZR��{R�feP;Y�gBY*�{R�T�V*fbfPS|_PSUIR�` dFR�T�giYxTI`#V�[FvwRrgiY\T�UIm_R�TXR�V*fbÏØ�BY\TIfeMUXT�V\v�R�PyPSUI]FMONZR�Mh���(m_NQP�dFR�T�giYxTI`#V�[FvwR�V\MD�xV�[DUWV*s\R�NeP;[KY\U�[_R�vwR�PXPIV�TINZfb|aTIRJªFR�vwUXR�MaNZ[ } V�[FM�P�Yx`aR�ÏUXNZ`aR�P(TX]_[FP�vwYx]_[DUXR�TtUXYD��PSU�V*[ÐM_V*TWM¥MDNQPSÎ�PS]_^FP�|KP�UXR�`ødFR�TSgiY\TX`#V*[Fv�Rr`aR�UXTINev�P�P�]Fv�múV\PtTXR�no]KR�P�UTXR�P�dFY\[ÐP�RrUXNZ`aR�`aR�V�[#V*[ÐMÓ�xV*TXNQV*[ÐvwR{�

² Ü°U�NQPtPSm_Y���[�UImFV�U�UXm_R�n{]FV�[DUXNZUS|)V*[FM�MDR�U�V*NbfÖY�gBmFV*TWMD��V�TIR�ϾP�dFR�vwNkjªvrNZ[OgiY\TI`ÕV*UINbY\[)TIR�n{]_NZTXR�MÓ^O|V�MDNeP�Î¥TXR�n{]_R�P�UäPIv�m_R�MD]KfZR�T�NQPrV&gi]_[Fv�UINZYx[ÛY*g�UIm_R#V�fZsxY\TINbUIm_` vwY\`adKfZR�ÔONZUS|{���{NZ`pd_fZRpPIv�m_R�MD]KfZÏNb[_s�V*fbs\Y\TXNZUXm_`#P�s�V*Nb[&fZNbUIUXfZR�d5R�T�giY\TX`#V*[ÐvwRt^FR�[_RwjÐU;giTXY\`÷R�ÔOUIR�[FP�Nb�{RtMDNeP�Î#MOTINZ�{R�P�dFR�v�Nåjªv�V�UINbY\[FP��~ Yx`ad_fZR�Ô#PIv�m_R�MD]KfZNZ[Ks#V*fbs\Y\TXNZUXm_`#Pw�FY\[úUImKRrY\UXm_R�T�mFV�[FMh�hTXR�no]KNZTIRävwY\`pd_TIR�mKR�[FP�Nb�{R�MDNQPSÎ&MOTINZ�{RvwYx[DjFsx]_T�V�UINZYx[�V�[FM&PSU�V*UXRrNb[DgiY\TX`#V*UXNZY\[±�

² Ü°U(NeP(PSm_Y���[ÓUXmFV*U�MDNQPSÎ TXR�n{]_R�P�UBPXv�m_RcMD]_fZR�T�P�UXmFV*UBRwéªR�vwUXNZ�{R�fb|rR�ÔOd_fZYxNZUBV�MDNeP�Î�MDTXNZ�{R{ç PlYx[_Ïi^5Y�V*TWMM_V�U�V#v�Vxv�m_R�d_TIY��ONQMDRäP�]_dFR�TXNZYxT�dFR�TSgiY\TX`#V*[Fv�R{�t�&R�V�[�TIR�PSdFY\[FPSR UXNZ`aR�P�giYxTt`aR�MONZ]_`aÏiUIYxÏØmKR�V��D|�BY\TIÎOfZY�V\M_P�MOR�vwTIRcV\P�RÕP�NZsx[_Nåj5v�V*[OUIfb|"��m_R�[ÛV�MDNQPSÎ"TXR�n{]_R�P�UäPIv�m_R�MD]KfZR�T�TIR�YxT�MDR�TWP�YxT�vwY\`�^_NZ[KR�PMDNeP�ÎaTXR�n{]_R�P�UWP(UIY�Nb`ad_TIY��{R�Y\[_Ïi^FY{V�T�M�v�Vxv�m_R�]_UXNZfbNZÙ�V�UINZYx[��

² Ló��NQMDR��\V�TINbR�US|ÓY�g�PIv�m_R�MD]_fbNZ[_spV*fbs\YxTINZUXm_`#P�V*[FM&Nb`ad_fbR�` R�[DUWV*UINbY\[FPBV*TXR�vwY\`adÐV*TIRcMÓV�[FMúvwY\[_ÏUXT�V\PSUIR�M�]FP�Nb[_s�MDR�UWV*NbfZR�M�P�Nb` ]KfQV*UXNZYx[tMDTXNZ�{R�[�^D|tUXT�VxvwR�P�Y*gKTIR�V�fZÏi�(Y\TXfQM�MDNeP�Î�V�[FMrPS|_PSUIR�`óVxvwUINb�DNbUS|{�

�,��³ î �2���´��������2 + � +�, �2'���÷� *���.�t������ + ��(m_NQP�MDNePIPSR�TIUWV*UINbY\[�NePyY\TXs{V*[KNZÙ�R�M�NZ[�R�NZs\mOU�v�mFV*dKUIR�TWPw� ~ mFV*d_UXR�T 5#MDR�PIv�TINZ^FR�P�VÕ�xV�TINZR�U�|#Y�g�NZ[OgiY\TIÏ

`#V�UINZYx[�dFY\UIR�[DUXNQV*fbfZ|�]FPSRwgi]_fFUIY�UImKR�MDNQPSÎ�PIv�m_R�MO]_fZR�T�� ~ mFV*d_UXR�T*7�MDNQPXvw]FPIPSR�Pd_TIR��DNbY\]FP2MDNeP�Î�PXv�mKR�MD]_fbNZ[_sP�UX]FMDNbR�Pw� ~ mFV�d_UIR�T�8)MDR�PIv�TINZ^FR�P�UImKR�`aR�UImKYOMDY\fbY\s\|)R�`ad_fbY�|{R�M UImKTIY\]Ks\m_Yx]_U�UIm_NePy�(YxTIΪ�hNZ[Fv�fZ]FMDNb[_spVMDNePIvw]FPXP�NbY\[¥Y�gtUXm_RaUITWV\vwRcM"�(YxTIÎOfZY{VxM_P�V*[ÐM³UXm_R#PSNZ`�]_fQV�UIY\T�� ~ mÐV*d_UXR�T�P � V�[FM´C�vwYx`adFV*TXR �xV�TINZYx]FPV*fbs\YxTINZUXm_`#PÖgiY\T�vwR�[OUITWV*fZNbÙ�R�M�PIv�m_R�MD]_fbNZ[_s�V�U(UImKRtm_Y{PSU�V�[FMaMDNeP�Ϊ�DTIRcP�dFR�vwUXNZ�{R�fb|{� ~ mFV�d_UIR�T A vwYx`adFV�TIR�PUImKR�PIV*`pR�V*fbs\YxTINZUXm_`#P�]FP�Nb[_s#MDNeP�UXTINZ^K]_UIR�M�PXv�mKR�MD]_fbNZ[_sK� ~ mFV�d_UIR�T D dKTIY��DNeMDR�P�P�Yx`aR�vwYx[Fvwfb]FMDNZ[KsaTIR�Ï`#V�TIÎKPrV*[ÐMòMONQPIv�]FPIPSR�P�gi]_UI]KTIR)MDNZTXR�vwUXNZY\[ÐPw�ú�(m_R)V*d_dFR�[ÐMDNZÔ¥fbNQPSU�PrdFV�T�V*`pR�UIR�T��xV*fb]_R�P�giYxT�UIm_R)MDNeP�ÎKP`aYOMDR�fZR�M Nb[#UIm_NeP(�(Y\TXÎh�

Page 17: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��� ��� ö ñ>/ ­

[ �.� , !��¢$&%B')����!���*�)� MÖ� ,{+ ��® ���� + �

L¼MDNeP�Î�TIRcno]_RcP�U�PXv�mKR�MD]_fbR�TTIR�Y\T�MOR�T�PBno]_R�]_R�P�Y�g.dFR�[FMDNb[_srTXR�no]KR�P�UWP�UIY�Y\d_UXNZ`aNbÙ�R�P�Yx`aR�P�R�U(Y*glvwTXNZÏUIR�TINQV } R{�âs_�Z�xd5R�T�giY\TX`#V*[ÐvwR�V�[FM´TXR�fZNeV*^_NbfZNbU�|�`aR�UITXNQv�P�����Ü°U`�]FPSUÖUXm_R�TIR�giY\TIR�mÐVc�{R�Vxv�vwR�PXPÖUIY�Nb[DgiY\TX`#V*UXNZY\[V*^FYx]_U�NZ[FMONZ�ONQMD]FV�f_TIRcno]_RcP�U�P�V*[FM UXm_R�P�U�V�UIRtY�g�UXm_Rtv�Y\`adFY\[KR�[DUWP2V*fZYx[_srUXm_R�ÜWÝxÞ�dFV�UIm��2�(m_NeP2v�mFV�d_UIR�TNQMOR�[DUXNåjFRcP��xV*TXNZY\]ÐP;US|Od5RcP(Y*g�NZ[DgiYxTI`#V�UINZYx[#UImFV�U�V*TIR�]FPSRwgi]_f�UXYaV�MDNQPSÎ TXR�n{]_R�P�U�PXv�mKR�MD]_fbR�T��

�(m_R�P�R�UyY�g2]FP�R�gi]_fÖNb[DgiY\TX`#V*UXNZYx[&NQP�MDNb�DNeMDR�MaNZ[OUIY�US�(YpvwfQVxPIP�RcPw�tÜ°[DgiYxTI`#V�UINbY\[agiTIYx` :X^FR�fZY��=< UXm_RPIv�m_R�MO]_fZR�T�TIR�feV*UIRcPyUIY)UIm_RpÜIÝ\Þ dFV�UImúmFV*TWMD��V�TIR{�.US|Dd_Nev�V*fbfZ|)vwYx[FvwR�TX[_NZ[_s#UXm_R�vwY\[OjFs\]_TWV*UXNZY\[±�Y\dFR�T�V�ÏUINbY\[��FV�[FM&v�]_TITXR�[DU�P�UWV*UIR�Y�g2UIm_R�Nb[FMDNZ�ONQMO]FV*f±vwY\[OUITXY\fZfbR�T�P��D^_]ÐP�R�P��FV*[FM)P�UIYxT�V�s\R�MOR��DNevwR�P } R{�âs_�Z�KMDNQPSÎ_P����Ü°[DgiY\TX`#V*UXNZYx[&giTIY\` :�V�^5Y��{R�<#UIm_RpPIv�m_R�MO]_fZR�T�P�dFR�v�NåjFR�P�m_Y�� TIR�n{]_R�PSU�PyTXR�fQV�UIR�UIY#R�Vxv�m�YxUIm_R�TrV�[FM"UXYP�|KP�UXR�`÷sxY{V*feP } R{� sK�Z�KV*d_d_fbNQv�V�UINbY\[#TI]_[OUINb`aR�P2V*[ÐMÓTIR�fZNQV�^_NZfbNZUS|rsx]FV*TWV*[OUIR�RcP����

­�?� MÖ� ,{+ ��® ���� + � �)� + ® µ��÷��� + ��¶ �2')� $&%B')����!����t�LßPXv�m_RcMD]_fZR�T.v�V*[�]FP�RBmFV*TWMD��V�TIR�ϾP�dFR�vwNkjªv�Nb[DgiY\TX`#V*UXNZYx[�UXYyTXR�MD]Fv�R�MDNeP�ÎtTXR�no]KR�P�U�P�R�TX�DNevwRUXNZ`aR�P���Ü°[

dFV�TIUINevw]_feV*T��KV*sxs\TIRcPIP�Nb�{R�MDNeP�ÎpPIv�m_R�MD]_fbR�T�PBv�V*[pR�ÔDdKfZY\NbU(Nb[DgiY\TX`#V*UXNZY\[pV*^FYx]_UtMONQP�ÎpMDTXNZ�{R�vwY\[DjÐs\]_TWV*UINbY\[V*[ÐM&P�UWV*UXR�UXY TXR�MD]Fv�Rt`aR�v�mFV*[KNQv�V�fhMOR�fQV�|KP�V*[FMa`#V�Î{Rt^FR�UIUXR�T�]FP�R�Y�g2Y\[_Ïi^FY{V�T�M�v�Vxv�m_RcPw�

· ?�¸(?�¸ £òE�<�¹ A=ºt<.75H¼»¼G�½o¾¼»¼7KGÀ¿B<L MONQP�Î8MDTXNZ�{R�vwYx[FP�NeP�U�P�Y*g�V)P�R�U�Y*g�ÁcP O ¤G¤�R b §rTXY\U�V�UINb[_s�Y\[ÛV)vwY\`p`aY\[úV�ÔDNePw�ÖYxT,§?Á ] £Q¦cPwR } PSR�R

jFsx]_TIR 5D� � �W�2ë(Y\UIm�§ `Qb?Â�O ¡HR�§tY*g�R�Vxv�madKfQV*UXUIR�T�V*TXR�vwY{V�UIR�Ma��NbUIma`#V�s\[_R�UINQv�`aR�MONQVD� u V�U�V�^_fZYOv�ÎKP(V*TXR��TINbUIUXR�[¥NZ[³vwNZTWvw]_fQV�T�¤ b�O ¡�Ã�§ÕYx[¥R�Vxv�mÛPS]_T�g¾VxvwR{�ú�(m_Ra`pNZ[_Nb` ]_`á]_[KNZUrY�g�M_V*UWV"PSUIYxT�V*sxR#NQP�]ÐP�]FV�fZfZ|V-§GR�¡B¤�Ä b �y��mKNQv�m US|Od_NQv�V�fZfb|òmKY\fQMKP �D� 5ò^O|DUXR�PaY*g´M_V*UWVßd_fZ]FP#PSY\`aR�m_RcV\MDR�T�Ý�UXT�V*NbfZR�T#Nb[DgiY\TX`#V*UXNZY\[} R�� s_�b��R�TITXY\T2v�Y\TITXR�vwUXNZY\[äM_V*UWVo�W�2L-¡\4cP ] £c¦QR b NePVtPSR�UÖY�gªUIT�Vxv�ÎKP } Y\[_R(giTXY\`óR�V\v�m�PS]_T�g¾VxvwR\��Rcno]_NeMDNQPSU�V�[DUgiTIYx`óUIm_RBvwR�[OUIR�ThY*gÐUIm_RBMDNeP�Ϊ�æ_Y\T�R�ÔKV*`pd_fZR{��UIm_RBY\]_UXR�TI`pY{P�U.v�|DfbNZ[FMDR�T�vwYx[DUWV*NZ[ÐPhUIm_RBY\]_UXR�TI`aY�P�U�UXT�V\v�ÎY*g�R�Vxv�m)P�]KT�g¾V\v�R{�2�2V\v�m&PS]_T�g¾VxvwR�mFV\P�V*[)VxPIP�YOv�NQV*UXR�M b R O ¦�Å�Æ b�] ¤�R�©cR O ¦��2Ü°[#`aY�P�U�MOTINZ�{RcP�Y\[KfZ|aYx[_RTIRcV\M5Ý���TINZUXR�m_R�V\MaNeP�V\vwUXNZ�{R�V�UtV�[D|asxNZ�{R�[pUINZ`pR{�.�(m_R�m_R�V\MKPyV�TIR�`aY\]K[DUXR�M Y\[àMDNQPSÎ OÇb�È §yUXmFV*U�V*TXRs{V�[_s\RcM�UXY\s\R�UIm_R�T�Y\[úVavwYx`a`aYx[ O ¡B¤ `QO ¤�Ä b ���2V\v�múvw|DfbNZ[FMOR�T�Y*g�M_V�U�VaNQP�V\v�v�R�PIPSR�MÓgiTIYx`øV#PSd5RcvwNåjªvV\v�UI]FV�UIY\T�dFY{PSNZUINbY\[��UÉÊÌË�Í6ÎSÏÍ6ÐTÑÌÒwÓ�ÔgÕwÍ6Ð�ÖÎSÒ�Ô«Ñw׬Ø?Ó�Ð�ÕwÍ6ÎSÍ6Ó�Õ�ÙQÍ6Î=ÏTÔ�Õ=ÚBÓ�ÑÌÛ«Ü=Ó�Ð�Ó�ÑÌÓ�ÕwÕ�Ô�ÒSÝ�ÎSÛ�Þ|ÕSß6Í6ÖJÏ?ÎSß6Ý�à^ÒwÓ�áBÛJÕSÍ6ÎwÍUÛ«Ð�ÎSÏ�ÓâÔ«ÑÌÎSãTÔ�ÎSÛ«Ò=ä�Ï�Ó�Ð

ÕSä�Í6ÎÌÑSÏ�ÍUÐ�Ö=ÚBÓ�ÎtämÓ�Ó�Ð ÎwÒ�Ô«ÑS×?ÕQÛJÐ ÔyÑÌÝ?ßUÍ6ÐTØEÓ�Ò�åcæçÍ6ÖJÏ?èSÑ�ÔgáBÔJÑÌÍ6ÎtÝ�ØEÒSÍ6éJÓ�ÕQã�ÕSÓ^ê�ëGìgíBî,ïoðoìJê�ñgêQÓ�Ü^ÚTÓ°Ø�Ø?Ó�Ø�ÚBÓ�Îtä�Ó�Ó�Ð�ÕSÓ�ÑÀÎSÛJÒwÕÛgò�Ø�ÔgÎÌÔ�ÎSÛ=Ô�ßUÍ6Ö«Ð^ÎSÏ�Ó�ÒwÓ�ÔJØ�ógä�ÒSÍ6ÎwÓôÏ�Ó�ÔJØ�õSÛgé«Ó�ÒSö=Ô%ÎSÒÌÔJÑw×Hå

8

Page 18: Aggressive Centralized and Distributed Scheduling ofDisk Requests

÷�ø�ø�ùÀúHûGüEúþýVÿ��Ìù��� ÿ���� ùÀú����ùÀúHûGü�úþý ÿ��Ìù

�TùÌÿ� ���� ú�� �jù��ÇùÌÿ�

��� ������ �ùÀú

�Túþÿ����ûGù�������ú

�ú�!

"���jüEÿ�����ú

(^]S_�`Qb R$#&%('*) u NQPSΠu TXNZ�{R���R�TI`pNZ[_YxfZY\sx|

�&R�v�mFV*[_Nev�V*fOMOR�fQV�|KPqY�giUIR�[äMDY\`aNb[FV*UXRBMDNQPSÎ�TXR�n{]_R�P�U�P�R�TI�ONQvwR2UINb`aR�P����qY�V\v�vwRcPIP.VyTIR�n{]_R�PSUIR�M�`aR�MDNeVfZYOv�V*UINbY\[��FV�MONQP�ÎpV\v�UI]FV�UIY\T�`�]FPSU�jFTWP�U=§?R�R�Ã#UIY�UXm_RtU�V�TIsxR�U�vw|OfZNZ[ÐMDR�T�V�[FM#V\vwUXNZ�xV*UXRtUImKR�V*d_dKTIY\dKTINQV�UIRTIRcV\M5Ý���TINZUXR mKR�V\Mh�#�(mKR�[��.VÓTXR�no]KR�P�UtNb[Fvw]_TWP b Äo¤ O ¤ ] Ä�£ O P�P O ¤�R�£c¡\4Û��m_NZfbR���V�NZUINb[_sagiY\T�UIm_R�U�V�TIs\R�UP�RcvwUIYxT�P�UXY�TIYxU�V*UXR#NZ[OUIY#dFY{P�NbUINbY\[��úL;giUXR�T�UIm_R�PSR#MDR�feV�|_P��ÖUImKRa`#V*sx[_R�UXNQv�`aR�MDNeVÕNePrVxv�vwR�PXP�R�MúV\PrUXm_RP�RcvwUIYxT�P�TIY\UWV*UXR-:I]K[FMDR�T <�UXm_R#TIR�VxM5Ý���TXNZUIR)m_R�VxMh�ßæ_]_TXUIm_R�T�`aR�v�mFV*[_Nev�V*fBMDR�fQV�|_PrTXR�P�]KfZU�Någ�`�]_fZUXNZd_fbRUITWV\v�Î_P(YxT�vw|OfZNZ[ÐMDR�T�P2` ]ÐP�U(^FRäV\v�vwRcPIP�RcMh�

Ü°[§V\M_MDNbUINbY\[§UIYÛUIm_R�`pR�v�mÐV*[_Nev�V*f�v�mFV�T�VxvwUIR�TXNQPSUINQv�Pw��V¥[D]_`�^FR�T�Y*gä`aYOMDR�TX[§MDNQPSÎògiR�V�UI]_TXR�Pav�V�[MDNbTIR�vwUXfZ|8VcéªR�vwUpPIv�m_R�MO]_fZNb[_súV*fbs\Y\TXNZUXm_` d5R�T�giY\TX`#V*[ÐvwR{���{Y\`aRÕV*TIR)UIm_R)TIR�PS]_fZU�Y�g�RwéªY\TXU�P UXY"`ÕV*Î{RMDNeP�ÎKP�P�R�fkgiÏ°vwYx[DUWV*Nb[_R�MtY\T�P�R�fkgiÏØ`ÕV*[FV�s\R�Mh� ~ fbR��{R�Th`pR�UIm_YOMKP5Y*gÐNZ[FvwTXR�V\PSNZ[_s�MOTINZ�{Rlv�V*dFVxvwNZUS| } R{� sK�Z��Ù�Yx[_R�P��V*[ÐM�RwéªR�v�UINZ�{R�fZNkgiR�UINb`aR } R�� s_�b��V*]KUIY\`ÕV*UINev�MDRwgiR�v�Uy`#V�[FV*sxR�`aR�[OUw��V*feP�Y#mFV��{R�Va`#V*ùSYxTyNb`adFV\v�U����(m_RTIR�`#V*Nb[FMDR�T�Y*g�UIm_NeP�PSR�vwUXNZY\[úd_TXY*�ONQMOR�PtV\MKMDNZUXNZY\[ÐV*fBMDR�UWV*NZfePtY\[¥`aRcv�mFV�[_NQv�V*f�dFY{PSNZUINbY\[_Nb[_s�MOR�fQV�|KPw�hUXm_RY\[KÏØ^FY{V�T�M#MDNeP�Î�vwYx[DUXTIY\fbfZR�T��*UXm_R�`#V*d_dKNZ[_stY�g�fbY\s\Nev�V*fªM_V�U�V�^_fZYOv�Î_P.UIYrdKmD|KP�Nev�V*f_`pR�MDNQV�fZYOv�V*UINbY\[FP��OV*[FM`aR�UXm_YOM_P�giYxT�Y\^_UWV*NZ[KNZ[_spMDNQPSÎ#MDTXNZ�{R�PSU�V*UXR�V*[FM)vwY\[DjÐs\]_TWV*UINbY\[�Nb[DgiY\TX`#V*UXNZY\[±�

! R�¡�© O £ ] ¡ O P 2 Ä�§ ] ¤ ] Ä�£ ] £ _zÖY{PSNZUXNZY\[KNZ[_s�VtTIR�VxM5Ý���TXNZUXR�m_R�V\M�UIY�Vxv�vwR�PXPP�dFR�vwNkjªv�P�RcvwUIYxT�PY*gqM_V*UWV�Nb[D�{YxfZ�{R�P.P�R��{R�T�V�fDNb[FMDNZ�ONQMO]FV*f

MDR�feV�|_P����Yrv�Y\TITXR�vwUXfZ|�d_TIRcMDNQvwU.UImKR�d5Y�P�NbUINZYx[_NZ[Ks�UXNZ`aRcPqY�g�dFR�[FMDNb[_s�TIR�n{]_R�PSU�P��{V�PIv�m_R�MD]_fbR�T.` ]FPSUÖmÐVc�{RV\v�vw]_T�V�UIRpV*d_dKTIY�ÔDNb`#V*UXNZYx[FPyY*g�UXm_RpP�R�R�Îàvw]_TX�{R{��m_R�V\MúP���NbU�v�m"UXNZ`aR��5��TXNZUIR�PSR�UIUXfZNb[_s#UINZ`pR{�5TXY\UWV*UINbY\[P�dFR�RcMh�FV*[FM)vw]_TXTIR�[OU(dFY{PSNZUXNZY\[)Y*g2UXm_R�MDNQPSÎaVxvwUI]ÐV*UIYxT��

L�§GR�R�Ã�¡ `cb,+ Rr`ÕV*dFPPSR�R�ÎäMDNQPSU�V*[ÐvwR�PUIY�V\v�UI]FV�UIY\T2dFY{PSNZUXNZY\[KNZ[_s�UINZ`pR�Pw���(mKRtPSR�R�ÎrUXNZ`aRB^FR�US�(R�R�[US�(Yävw|DfbNZ[FMOR�T�PÖNeP2VrvwYx`ad_fZR�Ô�gi]_[Fv�UINZYx[ Y�g.UIm_R�dFY{PSNZUINbY\[FP(Y�g.UIm_R�vw|OfZNb[FMDR�TWP } N¾� R{�b�\UIm_R�NZTBMDNQPSU�V�[FvwR�giTIY\`UImKR#P�d_Nb[FMDfbR\���.UIm_R#MONZTIRcvwUINbY\[úY*g�UImKR#P�R�R�Î } NZ[O��V�T�M"YxTrYx]_US��V*TWM5����xV�TINZYx]FPrR�[O�DNbTIYx[_`aR�[OU�V�fqg¾VxvwUIYxT�P} R�� s_�b�{�DNb^_T�V�UINZYx[aV�[FMaUIm_R�TI`#V�f_�xV*TINeV*UXNZY\[ª���DUXm_RtUS|Od5R�Y*g�P�R�TI�{Y�NZ[DgiYxTI`#V�UINbY\[ } MDR�MONQv�V�UIR�Mh�{R�`�^FR�M_MDRcMh�

Page 19: Aggressive Centralized and Distributed Scheduling ofDisk Requests

C

Y\T�mO|D^KTINQMF���FUIm_R�`#VxPIP�V*[FM�ªFR�ÔONZ^KNZfZNbUS|aY*gBUImKR�m_R�V\MFÝ�V*TX`ÑV\PXP�R�`�^_fZ|��_UIm_R�vw]KTITIR�[DU�V��\V�NZfeV*^_fbR�UIYaUXm_RV\v�UI]FV�UIY\T���R�U�v\�)L÷P�Nb[_s\fbR#vw]_TX�{Rav�V*[¥UXm_R�TIR�giY\TIRpY\[_fb|�TIR«ªFRcvwUr`aRcV*[úY\Tr]Kd_dFR�TIÏi^FY\]_[FMÛR�P�UXNZ`#V�UINbY\[FPgiY\T�PSR�R�Î�UINb`aR�Pw����|Od_NQv�V*fªP�R�R�Î#vw]_TX�{R�P(vwYx[FP�NeP�U�Y�g2V�[ÓNbTITXR�s\]_feV*T�Nb[_NZUXNQV*fFTXR�s\NbY\[agiY\T��{R�TI|�PSm_Y\TXUtPSR�R�ÎKPw�V `aNeM_MDfbR�TXR�s\NbY\[àV*d_d_TXY�ÔDNb`#V*UXR�MÓ^O|)VaPIn{]FV*TXR�TIY{YxU�gi]K[FvwUINbY\[��ªV*[ÐM"V feV*TXs\R�fZNb[_R�V�TyTXR�s\NbY\[&giY\T�fZY\[KsP�R�R�Î_P } P�R�RtjFsx]_TIR 5O�65�V*[FM#UIm_R�V*dKd5R�[FMDNZÔF���

�(m_RZ©cR O ¦ §«Æ ] ¤�¡�© UINb`aR } N¾� R{�b�tUIm_R�UXNZ`aRÛ[_R�v�R�PIPXV*TI|óUXY>R�fZR�vwUXTIYx[_NQv�V�fZfb|¼PS��NZU�v�m giTIYx` Yx[_RTIRcV\M5Ý���TINZUXR&m_RcV\MßUIY³V*[_YxUIm_R�TÕV*[FMßTXR�V*fbNZs\[ :IY��{R�T <"UIm_R)[_R��áUITWV\v�Î5��MOR�dFR�[FM_P dKTINZ`ÕV*TINbfZ|úY\[�UXm_RUS|DdFR�Y�g�P�R�TI�{YaNb[DgiY\TX`#V*UXNZY\[)]_UINbfZNbÙ�R�MÓ^O|&UXm_R�MDNeP�Î�MOTINZ�{R } R{� sK�Z�ªMDR�MDNev�V*UXR�Mh�hR�` ^FR�M_MOR�Mh�FY\T�mD|O^_TXNQM5�V*[ÐM³�xV�TINZYx]FPrR�[O�DNbTIYx[_`aR�[OU�V�fqg¾VxvwUIYxT�P } R�� s_�b�Ö�ONZ^_TWV*UXNZY\[³V*[FM¥UImKR�TI`#V�f�xV*TXNQV*UXNZYx[h���"��R�R�Î8V*[FM¥m_R�VxMP���NbU�v�m�VxvwUINb�DNbU�|pYOv�vw]_T�P�Nb` ]_fbU�V�[_R�Y\]ÐP�fZ|��D��NZUXmúP�R�R�ÎaUINb`aR�MDY\`aNb[FV*UXNZ[_sK�.-#L ��TINbUIR�TIRcno]_RcP�U�UImFV�UtTIR�Ïn{]_NZTXR�P�V PSR�R�Î#Y\T�m_R�VxM&PS��NZU�v�m#`#V�| [KR�R�M&VxM_MDNbUINZYx[FV*f.UINb`aR�UIYa`aYxTIR�v�fZY{PSR�fZ|ÕV*fZNbs\[)UIm_R�TIRcV\M5Ý���TINZUXRm_R�VxM } UIm_R�Æ b�] ¤�R�§GRX¤?¤EP ] £ _ UXNZ`aR\�W�0/

u NQPSÎ¥MOTINZ�{RpP�dFR�v�Nåjªv�V�UINbY\[FP�V*fZfbY�� TIY\UWV*UXNZY\[¢PSd5R�R�M_P�UXY��xV*TI|8P�fbNZsxmDUXfZ|&giTIYx` MONQP�ÎúUIYàMDNQPSÎh�à�(m_RTIYxU�V�UINZYx[¥PSdFR�R�M&Y*g;VaMDNeP�Î&`ÕVc|#R��{R�[&�xV*TX|ÓgiTIYx`ø`aYx`aR�[OU(UXYÓ`pY\`aR�[OU����&YOMDR�TI[8MDTINb�{R�Pyv�V*[�dFVxPIPV*[ÐM´TXR�vwR�Nb�{R�TXY\UWV*UINbY\[FV�f�PS|D[Fv�m_TXY\[_NbÙ�V*UXNZY\[�PSNZsx[FV*fePw�OV*[FM�V*[pR�ÔDUXR�TI[ÐV*fKPIv�m_R�MD]_fbR�T2v�V�[�UITWV\v�ÎrUImKRtPSd5R�R�MV*[ÐM"TIYxU�V*UXNZYx[FV*fBd5Y�P�NbUINZYx[¥Y*g;V&MDNeP�Î�^O|�`aY\[KNZUIYxTINb[_saUImKR�P�RpP�Nbs\[FV�fQPw�#ÜØg�UIm_R�[_R�vwRcPIPIV�TI|�`aYx[_NZUXY\TXNZ[_smFV�T�MD��V*TIR�NQP]_[FV��xV*NbfQV*^KfZR{�{V�[#V*sxs\TXR�PIPSNZ�{R�PIv�m_R�MD]_fbR�T2v�V�[aR�PSUINZ`ÕV*UIRBUIm_R�vw]_TXTIR�[OUTXY\U�V�UINbY\[FV�fhdFY{PSNZUINbY\[Y*g�V�MDNQPSÎa^D|pUIT�Vxv�ÎONZ[Ks�TIR�n{]_R�PSU�vwYx`ad_fZR�UINZYx[ UXNZ`aRcP�� �úY\TXU �x�  °�

��] §Gà Ä�£�¤ b ÄaPSPSR b�(m_R�TIR�PSY\]_TWvwR�PrV��xV*NbfQV�^_fZR�UXY&Y\[KÏØ^FY{V�T�MÛMDNeP�ÎúvwYx[DUXTIY\fbfZR�TWPyNZ[ÐvwTIR�VxP�R���NZUXm"R�Vxv�mú[_R��ãs\R�[KR�T�V�UINZYx[

Y*g;MDTINb�{R�Pw� ~ ]_TXTIR�[OU�MDNeP�ÎúMDTXNZ�{RävwY\`adFYx[_R�[OU�PtNZ[Fv�fZ]FMDR�dFY*�BR�T�gi]Kf�R�` ^FR�M_MOR�MÓ`aNevwTIYxd_TIYOv�R�PIPSY\T�P�V*[FMfQV�TIsxR�no]FV�[DUXNZUXNZR�P�Y*gª`aR�`pY\TI|��hLy[�Yx[_Ïi^5Y�V*TWMaMDNQPSÎ�vwY\[OUITXY\fZfbR�T.mFV*[FMOfZR�PÖUXm_R�dFR�TINbd_m_R�TWV*fO^_]FPNZ[OUIR�T�g¾V\v�R{�NZ[OUIR�TId_TXR�U�P.V*[FM�PSR�TI�ONQv�R�PÖMONQP�Î�TIR�n{]_R�PSU�P��\`#V*[ÐV*s\RcPqUXm_R�Y\[_Ïi^FY{V�T�MaM_V�U�V�v�Vxv�m_R��\V�[FM } NågªV�d_d_TXY\d_TXNQV*UXR�fZ|vwYx[DjFs\]KTIR�M5��`#V*Nb[DUWV*Nb[FPtV*[ÐMòPXv�mKR�MD]_fbR�Ptn{]_R�]_R�P�Y*g�dFR�[FMONZ[_s)TIR�n{]_R�PSU�Pw� u NQP�Îúv�Y\[OUITIYxfZfbR�TtjFTI`���V�TIRUS|DdKNQv�V�fZfZ|pvwYx[DUWV*NZ[ÐPyV�P�`#V�fZf�Yxd5R�T�V*UXNZ[_spP�|KP�UXR�` vwY\]Kd_fZR�Ma��NbUIm�V�[D]_`�^FR�T(Y�g2d_TXYOvwR�PIPSR�PyUXY dFR�TSgiY\TI`UImKR��xV�TINZYx]FP�MDNQPSÎ#vwY\[OUITXY\fbfZR�T2gi]_[FvwUXNZY\[ÐPw�×yY�P�U�Ü°[DUXR�T�g¾VxvwR

�&Y{PSUtMDNeP�ÎKP(dFY{PIPSR�PIP�P�]DÒÕvwNZR�[DU2Y\[KÏØ^FY{V�T�M�fZYxs\NQv�V�[FMad_TIYOvwRcPIP�Nb[_s�d5Y��BR�TyUXY�d_TIRcP�R�[OU�V´TXR�fQV�UINb�{R�fZ|vwfbR�V*[)NZ[OUIR�TSg¾V\vwRtUXY#V m_Y�P�U�P�|KP�UXR�`���×yNbs\m_ÏifZR��{R�fhd_TXY\UXYOvwY\fePw��PS]Fv�màV\PyUXm_R ��`#V*fbf ~ Y\`pd_]_UIR�T��{|KP�UXR�`Ü°[DUXR�T�g¾VxvwR } � ~ �OÜI�pV*[FM�UImKRúÜ [OUIR�fZfZNbs\R�[OU�zÖR�TXNZd_mKR�T�V�ftÜ°[OUIR�TSg¾V\vwR } ÜSz2ÜW�W��V*TXRúP�]_dKd5YxTIUXR�M ^O|�V"��NeMDR�xV*TXNZR�US|�Y*g�MDNeP�ÎúMDTXNZ�{R{��MDNQPSÎúV*TITWV�|{�2ÜIÝ\ÞÚV\M_V�d_UIR�T��2V*[ÐM³mKY{P�U�PS|_PSUIR�`Ñ`#V�[D]Dg¾VxvwUI]KTIR�TWPw�#L m_Y�P�U�YxTNZ[OUIR�TI`aR�MONQV*UXR�vwY\[OUITXY\fbfZR�T�NePIP�]KR�PyVrTXR�n{]_R�P�U�UXYaV�MDNeP�Î#MDTXNZ�{R�NZ[#UXR�TI`#P2Y*gBV�P�UWV*TXUINZ[KsPSÄ _a] ¡ O PB3QPSÄ�¡�ã `cÈ 3%R b } ��ë�����V�[FM¥V&UIYxU�V�f(TIRcno]_RcP�U�P�NbÙ�R{�)�(m_R#MDR�UWV*NbfQP�Y�g�UIm_RÕP�]_^FPSR�n{]_R�[OUr`aR�MONQVaVxv�vwR�PXPrV*TXRm_NeM_MDR�[�giTIYx` UXm_RymKY{P�U��(�(mKNQP(V�d_d_TXY{V\v�maY21aY�V\M_P(UXm_Rt`#V�[FV*sxR�`aR�[OUÖY��{R�TXm_R�VxM VxPIP�YOv�NQV*UXR�Ma��NZUXm UXm_RV\v�UI]FV�f�M_V�U�VúP�UIYxT�V�s\RagiTIYx` UXm_R#m_Y{PSU�Y\T�v�Y\[OUITIYxfZfbR�TrUXY�UIm_R#MONQP�Î8MDTXNZ�{R�R�fZR�v�UITIYx[_NQv�Pw�)LtPrV&TXR�P�]_fbU��PIv�m_R�MO]_fZNb[_saR�[OUINbUINZRcPyR�ÔOUIR�TX[FV*fUXY)VÓ`aYOMDR�TI[úMDTXNZ�{R�US|DdKNQv�V�fZfZ|#mFV��{R�fZNbUIUIfbRrYxTr[_Y#ÎO[_Y���fZR�MDsxR Y�g�UXm_R354 Ü=á�ÒSÛgéJÓ�Ü=Ó�Ð?ÎSÕ�Í6Ð�Ü�ÔgÖ«Ð�Ó�ÎwÍ ÑQÜyÓ�Ø?ÍjÔ*Ô�ÐTØyÕSÓ�ÒwéJÛ�ÎSÓ°ÑSÏ�Ð�ÛJß6ÛJÖ«Ý�ÑÌÛ«Ð?ÎSÍ6Ð?ã�Ó�ÎSÛyÍ6ÐTÑÌÒSÓ°ÔgÕSÓ�ÎSÒÌÔJÑw×�Ø?Ó�Ð�ÕwÍ6ÎSÍ6Ó�Õ�å76�ÛJÒ�òhã�Îwã�ÒSÓ

ÖJÓ�Ð�Ó�Ò�Ô�ÎSÍ6ÛJÐ�ÕmÛ�òÇØ?Í6ÕS×?Õ�Ù«ÒSÓ�áBÛJÕwÍ6ÎSÍ6ÛJÐ�Í6Ð�Ö%ÚTÓ�Îtä�Ó�Ó�Ð�Ô«Ø98�ÔJÑÀÓ�Ð?Î�ÎSÒÌÔJÑw×?ÕmÛ«Ð�Ô�Õwã�ÒtòþÔ«ÑÌÓ�Þ|Ítå Ó«åUÙ«Ô;:Àè ÑÌÝ?ß6Í6ÐTØ?Ó�ÒaÕSÓ�Ó�×�àaÜ�Ô°Ý*Ô«ÑÌÎSãBÔgß6ß6ÝÒSÓ�<Jã�ÍUÒwÓ�ß6Ó�ÕSÕ�ÎwÍ6Ü=ÓcÎwÏTÔgÐ�ÒwÓ�áTÛ«ÕSÍ6ÎSÍ6Û«Ð�Í6Ð�Ö*ÚBÓ�Îtä�Ó�Ó�Ð�ÎwÒ�Ô«ÑS×?ÕQÛJÐ�Ô^ÑÀÝGß6Í6ÐTØ?Ó�Ò�å=>�ÔgÎÌÔ^Ñ�ÔgÐ�ÚTÓ�ÕSãBÑ�ÑÌÓ�ÕwÕtòhã�ß6ß6Ý�ÒSÓ�Ô«ØyòhÒSÛ«Ü�ÎSÏ�Ó�Ü=Ó°Ø?ÍjÔ�Ó�éJÓ�Ð�ä�Ï�Ó�Ð,Ô^ÒwÓ�ÔJØ�ógä�ÒSÍ6ÎwÓ*Ï�Ó°ÔJØ�ÍUÕQÕSß6Í6ÖJÏ?ÎSß6ÝyÜ=Í6Õ�Ô�ßUÍ6Ö«Ð�Ó�ØHÙ?Ú�ã�ÎØ�Ô�Î�Ô%Ü^ã�ÕSÎ�ÚBÓ�ä�ÒSÍ6ÎSÎwÓ�Ð�ÔgÕ�ÑÌß6ÛJÕwÓôÎwÛ*ÎwÏ�Ó�Ü=ÍjØ�Ø?ß6Ó�Ûgò�Ô�ÎwÒ�ÔJÑw×�ÔgÕ�áTÛ«ÕSÕSÍ6Ú�ß6ÓQÍUÐyÛJÒÌØ?Ó�Ò�ÎSÛ�á�ÒwÓ�éJÓ�Ð?Î�ÑÌÛJÒwÒSã�á�ÎwÍ6ÛJÐ=Û�ò Ô«Ø98�ÔJÑÀÓ�Ð?ÎÎSÒÌÔJÑw×?ÕcÛ�ò Ø�Ô�Î�Ô�å

Page 20: Aggressive Centralized and Distributed Scheduling ofDisk Requests

A

90th Percentile Mean

|?0@

|?250A

|?500@

|?750A

|?1000

|?1250

|?1500

|?1750

|?2000

|B0.0

|B5.0

|B10.0

|B15.0

|B20.0

Seek Distance (cylinders)

See

k T

ime

(ms)

} Vo��æÐ]KfZf�PSR�R�Î#v�]_TI�{R

90th Percentile Mean

|C0D

|C10

|C20

|C30

|C40

|C50

|C60

|C70

|C80

|C90

|C100D

|E0.0

|E1.0

|E2.0

|E3.0

|E4.0

|E5.0

|E6.0

|E7.0

Seek Distance (cylinders)

See

k T

ime

(ms)

} ^h���lÔOdFV�[FMDR�Ma�ONZR��§Y*glP�m_YxTIU�P�R�R�Î_P(^]w_�`cb R$#&%F#&)��&RcV\P�]KTIR�M&�{R�R�Î ~ ]_TX�{R�P�giY\T�UImKR´��R�V*s�V*UIR��O��8 � C >D� � u NQP�Î u TINb�{R

Page 21: Aggressive Centralized and Distributed Scheduling ofDisk Requests

D

d_mO|_PSNQv�V�fªM_V*UWV�fQV�|{Yx]_U��{UImKR�P�UWV*UI]ÐP�Y*g.UXm_RtYx[_ÏØ^FY�V*T�M#M_V�U�V�v�Vxv�mKR{�OV*[FM UXm_R��\V�TINbY\]FP(Y��{R�TXm_R�V\M�MDR�feV�|_PV\PXP�YOvwNeV*UXR�MÓ��NbUIm#R�V\v�m#TIR�n{]_R�PSU��~ Y\[OUITXY\f.V�[FM ~ Yx`a` ]K[_NQv�V�UINbY\[#Þy�{R�TIm_R�VxM_P

L MDNeP�ÎaTXR�n{]_R�P�U�NZ[Ðvw]_T�P�PSR��{R�TWV*f.vwYx[DUXTIY\f�V*[ÐM&vwYx`a` ]K[_NQv�V�UINkY\[ÕMDR�fQV�|KP�MD]_TXNZ[_s�NZUWP;fbNågiR�UXNZ`aR{��Lys\Ïs\TXR�PIPSNZ�{R#PXv�mKR�MD]_fbNZ[_súV�fZs\YxTINbUIm_`#P�` ]ÐP�UrdKfQV*[ÛgiY\TpP�]Fv�m¢MDR�feVc|KP�UXY"^FR)RwéªR�vwUINb�{R{�úæ_Y\T�R�Ô_V�`ad_fbR{�ÖNkgV&MONQP�ÎúTIYxU�V�UINZ[Ks�V*U � 8 >T> � z2� } �x� � � `#PtdFR�TrTXY\UWV*UINbY\[h��TXR�n{]_NZTXR�P � `#PtY*g�v�Y\`a`#V�[FM&NZ[KNZUINeV*UXNZY\[Y��{R�TImKR�V\Mh�xVt`aR�MDNeV�V\v�v�R�PIPÖUXmFV*U��(Y\]KfQMr^FR�s\Nb[�NZ[ > � � `#P���NZUXm_Y\]KU2V*[O|rY��{R�TXm_R�V\M } sxNZ�{R�[�UIm_R�vw]KTITIR�[DUTIYxU�V�UINZYx[FV*f�dFY�P�NZUXNZYx[h�2��NZfbf%:iùS]FP�UB`aNQPXP°<�UIm_RtUWV*TXs\R�U�P�R�vwUXY\TWP(V*[ÐMÕ��V*NbU�giY\T�V�UIYxU�V*fªY*g �\� �6Cr`#P��ÜØg�UXm_RNZ[KNZUINeV*UXNZY\[�Y��{R�TImKR�V\M��(R�TXRyUWV*Î{R�[pNZ[OUIY�Vxv�vwYx]_[DU��OVrTIR�n{]_R�PSU���NbUIm#V�P�m_YxTIUXR�T�MDR�fQV�|�`aNZsxmDU2^FR�v�m_Y{PSR�[��

u NQPSÎrTXR�no]KR�P�U.d_TIYOv�R�PIPSNZ[_stY��{R�TXm_R�VxM_PÖMOR�dFR�[FMrY\[�UXm_R�TIRcno]_RcP�U.U�|OdFR } TIR�VxMrY\T��TXNZUIRx����UIm_R�TXR�no]KR�P�UP�NbÙ�R{�hUXm_R�P�UWV*UXR�Y*g�UXm_R�Y\[KÏØ^FY{V�T�M¥v�V\v�m_R } m_NbUyYxT�`aNQPXP����ªV*[ÐM�UXm_R�NZ`a`pR�MDNbV*UXR�fZ|�d_TIR��DNbY\]FPyTXR�n{]_R�P�U�çèPv�mFV*TWV\vwUXR�TINeP�UINev�Pw�.zTIYxUIYOvwYxfªV*[FM�^_]FPUITWV*[FP°giR�TBMDR�feVc|KPMDR�d5R�[FMrY\[�UIm_R�Nb[FMDNb�DNeMD]FV*fKvwYx`adFY\[_R�[OU�P�V*fZYx[_sUImKRaÜIÝ\ÞãdFV�UIm } R{� sK�Z�Fm_Y{PSUrd_TXYOvwR�PIPSY\TWPw�ÖNb[DUXR�TI`pR�MDNQV�UIR�vwYx[DUXTIY\fbfZR�TWPw��ÜIÝxÞ�V\M_V�d_UIR�T�Pw��^_]ÐP�R�P��V*[ÐM�Yx[_Ï^FY{V�T�M#MDNQPSÎ�vwYx[DUXTIYxfZfZR�T�P��W��(m_R�V*dKd5R�[FMDNZÔ�fbNQPSU�P`aR�VxP�]_TXR�MrY��{R�TIm_RcV\M��\V�fZ]_RcP�giYxT2UIm_R�×tz ~ 5T5�8 A MONQP�ÎMDTXNZ�{R{�Þ�[_Ͼë(Y{V*TWM u V�U�V ~ V\v�m_R

�(m_R�]FP�R�Y�g2`aR�`aYxTI|���NZUImKNZ[#R�`�^5RcM_MDR�M�MDNQPSÎ#MDTXNZ�{R�vwYx[DUXTIYxf�fZY\sxNQvymÐV\P�d_TIYxs\TIRcPIP�RcMÕgiTIYx`áP�`ÕV*fZf¾�P�dFR�RcMDÏØ`ÕV*U�v�m_Nb[_s�^_]DéªR�TWPÖUIY�MO|D[FV�`aNQv�V*fZfb|DÏi`pV*[FV�s\R�M�v�Vxv�m_RcP�vwY\[OU�V�NZ[_Nb[_stPSR��{R�TWV*fO`aR�s{V�^D|OUIRcPhY*gªPSUIY\TXÏV*sxR{�(Þ�[_Ïi^5Y�V*TWMÓMONQP�Î�fbY\sxNQv�v�V*[pV*]_UXY\`#V�UINev�V*fbfZ|rdKTIRwgiR�UWv�mäM_V*UWVrUIY�`aYxTIR�n{]_NQv�ÎDfb|�PIV*UXNQP°gi|�P�]_^FPSR�n{]_R�[OUTIRcV\MÓTXR�n{]_R�P�UWPw�2æ_Y\T�R�Ô_V�`ad_fZR��DV�MDNeP�Îa`aNbs\mOU(UWV*Î{R 5 > `#P�UXYaPSR�TI�ONQv�R�V´TXR�V\MaTXR�no]KR�P�U�UXmFV*U�TIR�n{]_NbTIR�P`aR�MONQV&Vxv�vwR�PXPw�2��m_R�TXR�V\P�V"PS]_^FPSR�no]KR�[DU�PSR�n{]_R�[OUINQV�f(TXR�V\M¥TIRcno]_RcP�UrgiY\T�d_TXRwgiR�U�v�m_R�M8M_V*UWVàgiTXY\` UXm_RY\[KÏØ^FY{V�T�M�v�Vxv�mKR�`pNZs\mOU2U�V�Î{R�Yx[_fZ| � `#P��

�(m_R#R�ÔONQP�UXR�[FvwR�Y*g�V*[ÛYx[_ÏØ^FY�V*T�M�v�V\v�m_R#VcéªR�v�U�P�PIv�m_R�MO]_fZNb[_s�VxvwUINb�DNbUINZRcP�Nb[¥US�(Y���Vc|KPw�8æÖNZTWP�U��2VPIv�m_R�MO]_fZR�T�`#V�|)[_Y\U�^5RÕV*^_fbRaUIYàMDR�UIR�TI`aNb[_RrUXm_R#V\v�UI]FV�f�dFY�P�NZUXNZYx[òY�g�UIm_RÕV\vwUXNZ�{R�TIRcV\M5Ý���TINZUXRam_R�VxMVcgiUXR�T�VrTXR�V\M�TIR�n{]_R�PSU�êOV*]_UXY\`#V�UINevyd_TIR�giR�U�v�maVxvwUINb�DNbUS|r`#V�|�TIRcP�]_fbU�Nb[#P���NbU�v�m_NZ[Ksrm_R�VxM_P(Y\T�P�R�R�ÎDNb[_srUXYUImKR�[KR�ÔDU�vw|OfZNZ[ÐMDR�T��2�{R�vwYx[FMh�Kv�V\v�m_R�M#M_V�U�Vr^_fbYOv�ÎKP�v�V*[#^FR�V\v�v�R�PIPSR�M g¾V*T�`aYxTIR�n{]_NQv�ÎOfZ|�UImÐV*[#^_fZYOv�ÎKPY\^KU�V*Nb[_R�M giTIYx`÷UImKR�MDNQPSÎ `pR�MDNQVO���Ov�m_R�MO]_fZR�TWP`#V�| sxNZ�{R�d_TINbY\TINbUS| UXY�TIR�VxMÕTXR�n{]_R�P�UWP�UXmFV*U���NbfZfhmKNZU(Nb[UImKRrv�V\v�m_RtNZ[)V�[�V*UXUIR�`pd_U(UXY TXR�MD]FvwR�`aR�V*[pTIR�PSd5Yx[FP�R�UINb`aR�Pw�

�{Y\`pR�MDNQPSÎ_P�P�]Kd_dFY\TIU�UXm_RpV*^_NbfZNZUS|#UIYàP�Nbs\[FV�f���TXNZUXR TXR�no]KR�P�U�v�Y\`ad_fbR�UINbY\[úVxPrP�Y{Yx[ÛV\P�V*fbf�Y�g�UXm_RM_V�U�V�^_fZYOv�Î_PrTXR�V\v�m¥UXm_R#Y\[_Ïi^FY{V*TWM�v�V\v�m_R{�8�(m_R#Y\[_Ïi^FY{V�T�M�vwYx[DUXTIY\fbfZR�T�`aY��{R�PtUIm_RÕM_V*UWVàgiTXY\` UXm_Rv�Vxv�m_R#UXY"UXm_R&`aRcMDNQV)V*UpP�Y\`pRÓfeV*UXR�T dFYxNZ[OU�� �{Nb[FvwR)vw]_TXTIR�[OU�MDNeP�ÎÛNZ`adKfZR�`�Rw[OU�V�UINbY\[FP�]FP�R)�{Y\fQV�UINbfZR`aR�`pY\TI|8vwYx`adFY\[_R�[OU�PrgiY\TpUIm_Ràv�V\v�m_R{�(UXm_RúvwYx[DUXR�[DUWP´Y�g�UIm_Ràv�V\v�m_R�V�TIR�fbY{P�UpNåg�UXm_R&dFY��(R�T�g¾V*NZfePw�(�O §«¤3Æ b�] ¤�R�§t`#V�| UXm_R�TIR�giY\TIR�TXR�MD]FvwR�UIm_R�TIR�fbNQV*^KNZfZNbUS|rY*g�MDNQPSÎ#P�UXY\T�V�s\R�]_[KfZR�PXP�V\M_MDNbUINbY\[FV�fÖ`aRcV\P�]KTIR�PV*TXRrUWV*Î{R�[#UIY�dKTIY\UXR�vwU�v�V\v�m_R�MpM_V*UWV } R{�âs_�b�D[_Yx[_ÏØ�{YxfQV�UINZfbR�`aR�`aYxTI|�v�Y\`adFY\[KR�[DUWP(Y\T�]_[_Nb[DUXR�TITX]_d_U�V�^_fZRdFY��(R�T�PS]_d_d_fbNZR�P����

u NQPSÎ_P���NZUXm b R O ¦HG Ä�£HG Oob�b�]�+�O P.V*[ÐM5Ý�YxT�Æ b�] ¤�RIGgÄ�£HG Oob�b�]F+�O P�v�V*dFV�^_NZfbNZUS|aTXR�MD]FvwR�TXR�no]KR�P�U�PSR�TI�ONQvwRUINb`aR�PÖ^O|�UITWV*[FP°giR�TITXNZ[_säM_V*UWVrUIY�Y\T�giTXY\`�UIm_R�`aR�MONQV�:XY\]_UXÏØY�giÏØYxT�MDR�T��6<��(mFV*UBNQP��_P�RcvwUIYxT�P(V�TIR�V\v�v�R�PIPSR�MNZ[�UXm_R�Y\TWMDR�TUXmFV*U2UXm_R�TIR�VxM5Ý���TXNZUXRym_RcV\MrR�[Fv�Y\]_[OUIR�TWPÖUImKR�` TWV*UImKR�TUImÐV*[�NZ[�P�UXTINevwUIfb|rVxPIvwR�[FMDNZ[Ks���ë��Y\TWMDR�T��æ_Y\T2R�ÔKV*`adKfZR{��Någ±V*[�R�[OUINbTIR(UXT�Vxv�Î�Y*g±M_V*UWV�NePÖUIY�^FRyTXR�V\Mª�DV�MDNeP�Î���NZUIm�TXR�V\MOÏØYx[_Ï°V�TITXNZ�xV*fª^5R�s\NZ[ÐPUITWV*[FP°giR�TITXNZ[_s)M_V�U�V giTIYx`øUXm_R�`aR�MDNeV V�fZ`aY�P�U�NZ`a`pR�MDNQV�UIR�fk|pVcgiUXR�T�V*[O|�P�R�R�Î&YxTtm_R�VxM"PS��NZU�v�múMDR�feV�|_PV*TXR�vwYx`ad_fbR�UIR{���(m_NQPyRcPIP�R�[DUXNQV*fbfZ|�R�fZNb`aNZ[ÐV*UIRcP�TIYxU�V�UINZYx[FV*f�fQV*UXR�[Fvw|��y�(mKRrdFR�T�giYxTI`#V�[FvwRäV\MD�xV*[OU�V�s\R�NePfZRcPIP�giY\T�TXR�n{]_R�P�UWP(fQV�TIs\R�TyYxT�P�`#V�fZfZR�T�UXmFV*[àV´UXT�Vxv�Ϊ�

Page 22: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�&Y{PSUyYx[_ÏØ^FY�V*T�MúM_V�U�Vav�Vxv�mKR�P�vwY\[OU�V�NZ[)` ]_fbUINbd_fZR�v�Vxv�mKR�fbNZ[_RcPw�_Y\T�§?R _�È R�£a¤E§\�DUXY ^FR�UXUIR�T�PSR�TI�ONQvwR`�]_fZUXNZd_fbRPSUITIRcV*`#PFY*g±P�R�n{]_R�[OUINeV*fxTIR�n{]_R�PSU�Pw��{Yx`aRBMDNQPSÎ_PhjF[_R�ÏØUX]_[_RBv�V\v�m_R2dFR�T�giYxTI`#V�[FvwR2^O|�V*[FV�fZ|OÙ�NZ[KsMDNeP�Î�TIR�n{]_R�PSU(dFV�UIUIR�TI[FP�V*[FM#MD|O[FV�`aNQv�V�fZfb|r`aYOMDNkgi|DNb[_s�UIm_R�[O]_`�^5R�T�Y�g2PSR�s\`pR�[DUWP } V*[ÐMÕUXm_R�P�R�sx`aR�[OUP�NbÙ�R\�W�

�Ov�m_R�MD]_fbNZ[_s#NePIP�]KR�PrTIR�feV*UXR�M�UXY&g¾V\PSU���TINZUXR�Pw�.TIR�VxM5Ý���TXNZUXR�ÏØYx[_ϾV*TITXNZ�xV*f¾�(V�[FMÛMD|O[FV*`aNev�v�V\v�m_RpP�R�sxÏ`aR�[OU�V�UINbY\[#V�TIR�^FR�|{Y\[FMaUXm_R�PIvwYxd5R�Y*g2UXm_NQP�MONQPIPSR�TIUWV*UXNZY\[±�~ Y\`p`#V*[FM�Wy]KR�]_R�Nb[_s

�&YOMDR�TX[ßMONQP�γMDTINb�{R�P�v�V*[ÛmFV�[FMDfZR#`�]_fZUXNZd_fbRrYx]_U�PSU�V*[ÐMDNZ[_súTIRcno]_RcP�U�PtgiY\T�PSR�TI�ONQvwR�� Ä ÈFÈFO £c¦J ` R ` R ] £ _ Y��{R�TIfeV*dFPtd_TXYOvwR�PIPSNZ[_s)Y��{R�TIm_RcV\M&giY\T�NZ[ÐvwY\`aNb[_saTXR�no]KR�P�UWP���NbUIm¥`pR�MDNQVpV\v�vwRcPIP�giYxTrd_TXNZYxTTIRcno]_RcP�U�P��Á��Y\`aR)vwYx`a`#V*[ÐM"n{]_R�]_R�NZ[_s�Nb`ad_fZR�`aRw[OU�V�UINbY\[FP�V*fbfZY��÷UXm_R)MDNQPSÎßv�Y\[OUITIYxfZfbR�TrUXY"UWV*Î{R�V�[V\v�UINZ�{R�TXY\fZR�Nb[�PXv�m_RcMD]_fZNb[_s�d5R�[FMDNZ[KsaTIR�n{]_R�PSU�P } R{� sK�Z�_UXYaTIR�MO]FvwRr`pR�v�mÐV*[_Nev�V*fªfQV*UXR�[FvwNbR�P��W� u NeP�ÎàvwY\[_ÏUITXY\fbfZR�TWPtv�V*[úV�fQPSYÓNb[FvwTXR�V\PSRrUImKR�vwY\[Fv�]_TITXR�[Fvw|)^5R�U��BR�R�[)TIR�n{]_R�PSU�PyTXR�vwR�Nb�DNb[_s�P�R�TX�DNevwR{�r�{RcvwUINbY\[�8_� � �U5MDNePIvw]FPXP�R�P�PSR��{R�TWV*f�PSdFR�vwNåj5v�Yxd_UINb`aNZÙcV*UINbY\[FP��

ÜØgªVyMONQP�Î�PSR�TI�ONQvwRcPhTIR�n{]_R�PSU�PhNZ[äV*TXTINZ�xV�fDYxT�MDR�T��*R�ÔDUXR�TI[FV�fOPIv�m_R�MD]KfZR�TWPh[_R�R�M�Y\[_fb|�ÎO[_Y��¥UXm_R�MDR�d_UIm�Y*gUImKR(Y\[KÏØ^FY{V�T�M�vwY\`p`#V*[FM�no]_R�]_R{�.ÜØgFVtMONQP�Î�TIR�YxT�MDR�TWPqdFR�[ÐMDNZ[_s�TIR�n{]_R�PSU�Pw��R�ÔOUIR�TX[FV*fOPXv�mKR�MD]_fbR�T�P�PSm_Y\]_feMvwY{YxT�MDNb[FV*UXRrUImKR�NZT�V\vwUXNZ�ONZUS| ��NbUIm#UImKR�Yx[_Ïi^5Y�V*TWM�MDNQPSÎ#PIv�m_R�MD]KfZR�T } N°�âR{�Z�{]FPSR�MDNQPSUITINb^_]_UXR�M#PIv�m_R�MD]_fbNZ[_sO���

��O ¤ O¢��O 4mÄ ` ¤��V*[O|"R�ÔDNeP�UINb[_s)PIv�m_R�MD]KfZR�TWPy]FP�RÕP�NZ`pd_fZR���ë��yÏi^FVxP�R�M¥V�d_d_TXY*ÔONZ`ÕV*UINbY\[FPtY�g�P�R�R�ÎOÏiTIR�MD]ÐvwNZ[_s)V�fZs\YxÏ

TINbUIm_`ÕPw�§��ë��yÏi^FV\PSR�M PXv�mKR�MD]_fbNZ[_súTIR�fbNZR�PrYx[�m_NZsxm_fZ|üP�R�n{]_R�[OUINeV*f�fbY\s\Nev�V*f�^_fbYOv�΢[D]_`�^FR�T�UIY8d_mD|KP�ÏNQv�V*f2^_fZYOv�Îú[D]_`�^FR�T } ��ë��yÏØUXY\Ͼz2ë����t`#V�d_d_Nb[_s{P��&�&YxTIRpV*s\sxTIR�PXP�Nb�{R#V*fbs\Y\TXNZUXm_`#PtTIR�n{]_NbTIRpV\v�vw]KT�V*UXRÎO[_Y���fZR�MDsxR(Y�g�UImKR�M_V*UWVyfQV�|{Y\]KU��%YFYx[_R�MrTXR�vwY\TWMDNZ[Ks_�\UXT�V\v�ÎFÝ�vw|OfZNb[FMDR�T.PSÎ{R����{V*[ÐM�MDRwgiR�vwU.`#V�[FV*sxR�`aR�[OUPIv�m_R�`pR�P2vwY\`adKfZNQv�V*UIR���ë��yÏiUIYxÏ°z2ë��¼`#V*dKd_NZ[_s�Pw�YFY\[KR�M � R�v�Y\T�MONZ[_s

�qY�R�ÔDd_fbY\NbU�UXm_RtfeV*TIsxR�T�UITWV\v�Î�vwNZTWvw]_` giR�TIR�[Fv�R(Y*g�v�|DfbNZ[FMDR�T�PÖg¾V*TXUIm_R�T(giTXY\`�UIm_R�P�d_Nb[FMDfZR��DVr`pYOMDR�TI[MDTXNZ�{R�]FP�]ÐV*fZfb|#dFV*TXUINZUXNZYx[FP;NbU�P�P�R�U�Y*g�vw|DfbNZ[FMOR�T�P(Nb[DUXY `�]_fZUXNZd_fbR ¥ Ä�£cR�§x�y�(mKRr[O]_` ^FR�TBY*g�P�RcvwUIYxT�P�d5R�TUITWV\v�Î#NZ[FvwTXR�V\PSR�P���NZUIm�UXm_RrTWV\MDNb]FPyY�g(UXm_RrUXT�Vxv�ÎKPyNZ[)UIm_R�Ù�Y\[KR{��æ_Y\T�R�Ô_V�`ad_fbR{�_UIm_R�Y\]_UXR�TI`pY{P�U�Ù�Yx[_R`aNbs\mOU(mFV��{R�US��NQvwR�V\P�`#V�[D|pP�R�v�UIY\TWP;dFR�T�UITWV\v�Î#V\P�UIm_R�NZ[K[_R�TI`pY{P�U�Ù�Y\[_R{�B�(m_NeP;Nb[FvwTIRcV\P�RcP;^FY\UXm&UXm_Rv�V�dFV\vwNbUS|ÓdFR�T�]_[_NbUt�{Y\fb]_`aR�V�[FM&UImKR�`aR�V*[#`aRcMDNQVrUXT�V*[ÐP giR�TtTWV*UXRrY*gBUXm_R�MDNQPSÎh����NZUXm_NZ[)R�V\v�m&Ù�Yx[_R{�V#MDNQPSÎ�`#V�|&TXR�P�R�TX�{R�V)P�]_^FPSR�U�Y*g�vw|OfZNb[FMDR�TWP } Y\T�UIT�Vxv�ÎKPtY\T�P�RcvwUIYxT�P���giYxT�MDRwgiRcvwUt`#V�[FV*sxR�`aR�[OU } PSR�R^FR�fZY��t�W���T�V\v�Î#V�[FM ~ |OfZNb[FMDR�T��{Î{R��

�{NZ[ÐvwRtPS��NZUWv�m_Nb[_s�^FR�US�(R�R�[�UITWV\v�Î_P2V�[FMaP�R�R�ÎDNb[_s�^FR�US�(R�R�[pV\M�ùXV\vwR�[OU�v�|DfbNZ[FMDR�T�PÖTXR�no]KNZTIRcPÖ[_Y\[KÏØÙ�R�TIYUINb`aR{�.UIm_RajFTWP�U�fZYxs\Nev�V*fB^_fZYOv�Î¥Y*g�R�Vxv�mÛUITWV\v�Î"YxTav�|DfbNZ[FMDR�T�NePrY*é±P�R�U } Y\T3§?Ã�RXÆ R�¦l�tgiTXY\` UXm_RajFT�PSUfZYxs\Nev�V*f.^_fZYOv�ÎaY�g(UXm_RrdKTIR��ONZYx]FP;UXT�Vxv�ÎaYxT�vw|OfZNb[FMDR�T��(�(m_NePyd_TXR��{R�[OU�P�V�TIR�n{]_R�PSUyUXmFV*U�vwTIY�PIPSR�PtV UXT�V\v�ÎY\Tävw|OfZNZ[ÐMDR�T�^5Yx]_[FM_V�TI|"giTXY\` :iùS]FP�U�`aNQPXP�NZ[KsH< UXm_R [KR�ÔDU�fbY\s\Nev�V*f2^_fbYOv�ÎúV�[FM"��V*NZUXNZ[_s)V�fZ`aY�P�U�Vagi]_fZfTIYxU�V�UINZYx[agiY\T�NZUBUIY�vwYx`aR�V*TIYx]_[FM)V*s{V�NZ[��B��T�V\v�ÎpV*[FM#vw|OfZNb[FMDR�TBP�Î{R���P�V*TIR�s\R�[_R�T�V*fbfZ|pP�dFR�vwNkjFR�MaVxPyV�[NZ[OUIR�s\T�V�fh[O]_`�^5R�T(Y*g�P�R�vwUXY\TWP�V*[FM#UIm_R�TXRwgiY\TXR�MDNkéhR�T(giTIY\`áÙ�Yx[_R�UIY�Ù�Yx[_R{�

Page 23: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�?>

u RwgiRcvwU���V�[FV*sxR�`aR�[OUu NQPSÎ#MDTXNZ�{R�PBv�V*[àP�]_TX�DNb�{RtUIm_R�fbY{PIP(Y�g2mO]_[FMDTXR�M_P(Y*g�P�R�vwUXY\TWP(Y\T�UIT�Vxv�ÎKP(UIY�`pR�MDNQV�vwY\TXTI]_dKUINZYx[��2Ü°[

g¾V\v�U��ªV [_R��ãMDTXNZ�{R�]FP�]ÐV*fZfb|)vwY\[OU�V�NZ[FP�V fZNeP�U�Y*g�MDRwgiRcvwU�P(NeMDR�[OUINåjÐR�M#V*UtUXm_R�g¾VxvwUIYxTI|{��L MDNeP�Î#]_dªM_V*UXR�PUImKNQPÖfbNQP�U.��NZUXm�MDRwgiR�v�U�P _ab ÄHÆ�£�MD]_TXNZ[_stNbU�P�fZNkgiR�UINb`aR2V*[ÐMrTIR�`aY��{R�PhUXm_R�v�Y\TITX]_d_U`pR�MDNQV�fZYOv�V*UINbY\[FP�giTIY\`NZUWP���ë��yÏiUIY\Ͼz2ë��¼`#V*d_dKNZ[_sK�

�{R�vwUXY\T�Y\T�UXT�V\v�΢§?P ] ÁcÁ ] £ _ YOv�vw]_T�P�MD]KTINZ[Ks�MDNeP�ÎÓgiYxTI`#V�U���Ü°["UXm_R�v�VxP�R�Y*g�P�RcvwUIYxT�P�fbNZd_d_Nb[_s_��UXm_RgiY\TX`#V*U�d_TIYOv�R�PIP�PSÎDNbdFPrR�V\v�mÛMDR�giR�vwUINb�{RaPSR�vwUXY\T�V�[FMßVxM*ùS]FPSU�PrUImKR&��ë���ÏØUXY\Ͼz�ë���`#V*d_dKNZ[_sàP�YúUImFV�UUImKR�P�R�vwUXY\TWPyY\[úR�NZUXm_R�T�:�PSNQMDR�<�m_Y\feM&fZY\sxNQv�V�fZfb|&PSR�n{]_R�[OUINQV�fMKV*U�VO�r��T�Vxv�ÎàP�fbNZd_d_Nb[_s�giY\fZfbY���PyUIm_R�PXV*`aRTIYx]_UINb[_R{�(R�Ô_vwR�d_U�UImFV�UaUImKRÕgiYxTI`#V�U dKTIYOvwR�PXPaP�ÎONZdÐP V�[ßR�[OUINbTIR#UITWV\v�ÎòNkgtNbUav�Y\[OU�V*Nb[FP�V*[O|ßMORwgiR�vwUXNZ�{R`aR�MONQVD���2V\v�m�P�fbNZd_dFR�MaTXR�s\NbY\[�v�mFV�[_s\R�P(UXm_Rr`ÕV*d_d_Nb[_srY�gBP�]K^FP�R�n{]_R�[OU�fZYxs\Nev�V*f�^_fbYOv�ÎKPw�_TXR�MD]Fv�NZ[_s�UXm_RV\v�vw]_T�Vxvw|ÛY*g�VúPIv�m_R�MO]_fZR�T�UXmFV*UpTIR�fbNZR�P�Y\[§P�UWV*UXNQvÓÎO[_Y���fZRcMDs\R#Y*g�UXm_R�vw|OfZNb[FMDR�TäV*[FMFÝ�Y\TpTIY\UWV*UXNZY\[ÐV*fdFY{PSNZUINbY\[#Y*g�R�Vxv�ma^KfZYOv�Îh���(m_RtgiY\TI`ÕV*U2d_TIYOv�R�PIP�TIR�PSR�TI�{RcPlR�ÔDUXT�VrPSdFV\v�R } §?Á Oob R b R _�] Ä�£c§*�2V�U�UIm_RtR�[FMY*g�vwR�TXU�V�NZ[¥UXT�V\v�ÎKPw�2vw|OfZNb[FMDR�TWPw�ÖYxT�Ù�Y\[KR�P�UXYúvwY\[OU�V�NZ[ÛUIm_RÕP�d_NbfZfZY��{R�T�v�V�]FP�RcM"^D|³P�fZNbd_dFR�M¥PSR�vwUIYxT�PrYxTUITWV\v�Î_P } UIYa`pNZ[_Nb` NbÙwR�UIm_R�Nb`adFV\v�U(Y*g�MDRwgiR�vwUWP(Y\[�UXm_R�P�U�V�UINevr��ë��yÏiUIYxÏ°z2ë��¼`#V*dKd_NZ[_sO���BÜ°[&s\R�[_R�T�V�f°�fQV�TIsxR�P�dFV�TIR�TIR�s\NZYx[FP(V�éªR�vwU�PSR�R�Î�^FR�mFV��DNbY\T�V*[FM#P�`ÕV*fZfÐP�dFV�TIR�TIR�sxNZYx[FP } MDNQPSUITINb^_]_UXR�M VxvwTIY�PIP�UIm_R�MDNeP�ÎF�NZ[OUIR�TITI]Kd_U�PSR�no]KR�[DUXNQV�f�M_V�U�V�UIT�V�[FP giR�T�Pw�

/ R O PwPSÄ�¡ O ¤ ] Ä�£¥YOv�vw]_TWPy��m_R�[8V#MDNQPSÎ�MDNePIvwY��{R�TWPyMDR�giR�vwUINb�{R�P�R�vwUXY\TWP } Y\TtUXT�Vxv�ÎKP���MO]_TINb[_s#[_Y\TX`#V*fMDNeP�Î�]FPSR{��&YOMDR�TI[#MDNeP�ÎKP2V*]_UXY\`#V�UINQv�V*fZfb|�TIR�`#V�d�UIm_R�VcéªR�v�UIR�M���ë��tPUIYäP�dFV�TIR�TIR�sxNZY\[ÐP(V*[ÐM´TXR�MDNZTXR�vwUP�]K^FP�R�n{]_R�[OU�V\v�v�R�PIPSR�PyUIY)UIm_RpV*dKd_TIYxd_TINeV*UIRpP�dÐV*TIRÕP�R�vwUXY\TWPw���(m_R#MDNeP�ÎKPy]FPSR�M"NZ[�UXm_NQPt�BY\TIÎúv�Y\[OU�V*Nb[�{R�TX|´giR��§TIRcV*fZfbYOv�V*UXR�M#MDRwgiR�v�U�Pw�Od_TIYOMO]FvwNZ[Ks [_YpMDNePIvwR�TX[_NZ^KfZR�d5R�T�giY\TX`#V*[ÐvwRtRwéªR�vwUWPw�

�LK ¤ b�O ¡B¤ ] Ä�£FÄ Â���] §?à �4b�]�+ R 2=Oob�OoÈ RX¤�R b §�(m_RrdKTIR��ONZYx]FPyPSR�vwUXNZY\[ÐPyMDRcPIvwTXNZ^FR�V�[D]K` ^FR�T�Y�gBMDNQPSÎ)MDTINb�{R�dÐV*T�V�`aR�UXR�T�P(]FPSRwgi]_f.UIYpVaPIv�m_R�MO]_fZR�T��

�ÔDUXR�TI[ÐV*fFPXv�m_RcMD]_fZR�T�P�` ]FPSU.P�Yx`aR�m_Y��ÛY\^_UWV*Nb[�P�]Fv�m�NZ[DgiYxTI`#V�UINbY\[�giTXY\` VtMDNQPSÎrNb[rY\TWMDR�T2UIY�R�ÔDdKfZY\NbUÖNbU��Ü°[ dÐV*TIUXNQvw]KfQV*T��{V*fbs\YxTINZUXm_`#PUImÐV*U2TIR�MO]FvwR�vwY\`�^_NZ[KR�MrPSR�R�Î�V�[FM TXY\U�V�UINbY\[FV�f5feV*UXR�[FvwNbR�PÖTIRcno]_NbTIR�MDR�U�V*NbfZR�MNZ[OgiY\TI`ÕV*UINbY\[�Yx[¥vwYx`a`#V�[FMÓd_TXYOvwR�PXP�NZ[Ks&Y��{R�TImKR�V\M_P��h`aR�v�mFV�[_NQv�V�fÖfeV*UXR�[FvwNbR�Pw��V�[FMúM_V*UWVÓfQV�|{Yx]_U�����YR�[FV�^_fZR2UXm_R(]FPSR2Y*gªPS]Fv�mäV*fbs\Y\TXNZUXm_`#Pw��V�P�]KNZUIR2Y�gªno]KNQv�Î�V*[FM�RwéªR�vwUXNZ�{Rd_TXY\sxT�V*`ÕPhmFV��{R�^FR�R�[�MDR��{R�fZY\dFR�MUIY#R�ÔOUITWV\vwU�UXm_R�[_R�vwRcPIPIV�TI|�Nb[DgiY\TX`#V*UXNZY\[&giTXY\`0`aYOMOR�TI[¥� ~ �oÜtMDNQPSÎúMDTINb�{R�Pw��� �úY\TIU �\�  2v�Y\[OU�V*Nb[FPrV�[Y��{R�TI�ONZR���Y*g�UIm_R�R�ÔOUITWV\vwUXNZY\[#d_TXYOvwR�PXPw�

· ?�¸(? · M C5E�<.7ON*P M QSR CFE0¡BC R CK<LyfZUXm_Y\]Ks\m�UImKR&`aY�P�U�NZ`pd5YxTIUWV*[OU mFV�T�MD��V*TXR�Ï°PSdFR�vwNåj5v&M_V�U�V"TXR�fQV�UIR�P�UIY¥UXm_R�MONQP�΢MDTXNZ�{R�P���YxUIm_R�T

ÜIÝ\Þ0dÐV*UIm vwYx`adFY\[_R�[OU�Ppv�V*[óV�fQPSYßPS]_d_d_fb|�]FP�R�gi]_f�PIv�m_R�MO]_fZNb[_s¥NZ[OgiY\TI`ÕV*UINbY\[�� ë(]FP#V\M_V�d_UIR�TWP&v�V�[d_TXY*�ONQMORaUIm_R)vw]KTITIR�[DUäP�U�V�UI]FP�Y*g�NZ[OUIR�TI`aR�MONQV*UXR�V*[FM¥dFR�TXNZd_m_R�T�V*fB^_]FPSR�Pw�ÛÜ°[OUIR�TX`aR�MDNeV*UIR�v�Y\[OUITIYxfZfbR�T�P��NZUXm#P�]OÒ#vwNbR�[OU(v�Y\`ad_]KU�V*UXNZYx[aV�[FMa`aR�`aYxTI|�TIR�PSY\]_TWvwR�P�v�V�[ad_TXY*�ONQMORy^FY\UXm)v�V\v�m_NZ[Ks�V*[ÐMÓPXv�mKR�MD]_fbNZ[_sgi]_[Fv�UINZYx[FV*fbNZUS|{�BÜ°[ÓdÐV*TIUXNQvw]KfQV*T��FMDNQPSÎ)V*TITWV�|&v�Y\[OUITIYxfZfbR�T�P�v�V�[�vwYx[DUXTINb^_]_UIR�PSNZs\[KNåjªv�V�[DUXfZ|aUXYaPXv�mKR�MD]_fbNZ[_sdFR�T�giYxTI`#V�[FvwR{�

u NQPSÎ¥V�TITWVc|KPrV�TIR#^FR�vwYx`aNZ[_s)vwYx`a`aYOMDNbUS|ÓNbUIR�`ÕP;giY\TäP�|KP�UIR�`#PtY*g�V*fbf�PSNZÙ�R�P��&L��\V�TINbR�US|�Y*g�M_V�U�Vd_feV\vwR�`pR�[DU�V*[ÐM"TIR�MO]_[FM_V�[Fvw|8PIv�m_R�`aR�P�V*TXR#V��xV*NZfeV*^_fbR UXY#NZ`ad_TXY��{RrdFR�T�giYxTI`#V�[FvwRpV*[FMFÝ�Y\T�MKV*U�V#TIR�ÏfZNeV*^_NbfZNbU�| � û�V*[_s � 8ª��×yYx] � 7_�.×yYxfZf � 5{�lû�TWVc| �B> �±��V�UIÙ�D � ��zV�UIUgDTD_�.��Nb`�DBCJ °��Ly[úNZ[OUIR�fbfZNZsxR�[OU�MDNQPSÎ�V*TXÏT�V�|¢vwYx[DUXTIY\fbfZR�T�v�V*[ßTXR�Y\TWMDR�T�dFR�[FMDNb[_s"TXR�n{]_R�P�UWP´^ÐV\P�RcMòY\[�UXm_R�PSU�V�UIR&Y�g�V*[O|¢v�V\v�m_R�P���MDNeP�ÎKPw�BV*[FM^_]FPSR�P�]K[FMDR�T�NZUWP�vwY\[OUITXY\f°��æ_Y\T�R�ÔKV*`pd_fZR{�ªNåg�V*[ÛV�TITWVc|�R�`ad_fZY�|KPyV#TIR�MO]_[FM_V�[Fvw|úPIv�m_R�`pRrUImÐV*U�d_TIYxÏ

Page 24: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�\�

�ONQMDR�P�` ]_fbUINbd_fZRadÐV*UImÐPÕgiY\TÕV\v�vwRcPIP�Nb[_s¢M_V*UWV } R{�âs_�Z��MDNeP�΢`aNZTXTIY\TXNZ[_sO����UImKRúV*TITWV�|§vwY\[OUITXY\fZfbR�TpvwY\]_feMMD|O[FV*`pNQv�V�fZfZ|)TIYx]_UIRaTXR�n{]_R�P�UWP�UXY�UIm_R#v�Y\`adFY\[KR�[DUWP�UXmFV*U�v�V�[¥`aY�P�U�n{]_Nev�ÎOfZ|àP�R�TX�DNevwR UXm_RaTXR�no]KR�P�UWP� z.Y\fZ| � 7O�\�{]_sxs � 7F�x�ys �O� � ~ m_R�[ �T> �\�hR�R �B> �xë(NZUXUgDTD� °�.LyfbUIR�TX[FV*UXR�fZ|���UIm_RBV*TXT�V�|�v�Y\[OUITIYxfZfbR�T�vwYx]_fQM�PIv�m_R�MDÏ]_fbR�TXR�n{]_R�P�UWP�UXY UXm_R�vwY\`adFYx[_R�[OU�P(��NZUXm#UIm_R�P�mKY\TIUXR�P�U�dFR�[ÐMDNZ[_spn{]_R�]_R�P��

Ü°[ UXm_NQPaMONQPIPSR�TIUWV*UXNZY\[±�tV*fbftNZ[OgiY\TI`ÕV*UINbY\[ßgiTXY\` :I^FR�fbY��=<³UXm_RúPIv�m_R�MO]_fZR�TpTIR�feV*UIRcP UIY¢MDNeP�Î�MOTINZ�{RvwYx[DjFs\]KT�V*UXNZYx[¼V�[FM PSU�V�UIR{� �Ov�m_R�MD]_fbNZ[_súY\dKUINZ`pNZÙ�V�UINZYx[FPr]FPSNZ[_sÛ^_]FPpV*[FM�NZ[OUIR�TX`aR�MDNeV*UXR#vwY\[OUITXY\fbfZR�TNZ[OgiY\TI`ÕV*UINbY\[#V�TIR�fZR�giU�V\P(gi]_UI]_TXR��(Y\TXÎh�

­�g­ MÖ� ,{+ ��® ���� + � �)� + ® µ;�� + � ��¶ �2')� $&%B')����!����t�Ü°UtNQP�R�V\PS|&UXYÓfbY{PSR�P�Nbs\mOUtY*gBUXm_R�:I^_Nbsad_NevwUI]_TXR�< ��m_R�[úMDR��{R�fbY\d_Nb[_s�PIv�m_R�MD]KfZNZ[KsaV�fZs\YxTINbUIm_`#P�UImFV�U

]FPSR�feV*TXs\R�n{]FV*[OUINbUINbR�PY*g�mFV*TWMD��V�TIR�ϾP�dFR�vwNkjªvtNZ[DgiYxTI`#V�UINbY\[����(m_RtR�[FMasxY{V*f�Y�g2MONQP�ÎpPIv�m_R�MO]_fZNb[_s�NQP([_YxUUIY�TXR�MD]FvwR�UImKR�`aR�V*[�MONQP�Î�TXR�n{]_R�P�U�TIR�PSd5Yx[FP�R�UINZ`pR{�*^K]_U2UIYrTXR�MD]Fv�R } Y\T2R�fbNZ`aNb[FV*UXR\�FUImKRydFR�TSgiY\TI`ÕV*[FvwRNZ`pdFV\vwU�Y*g¬:�PSfZY��=<¥MDNeP�΢V\v�UINZ�ONZUS|úY\[§V�d_d_fZNev�V*UXNZYx[òdKTIYOvwR�PXP�R�P��¼Ü°[DgiYxTI`#V�UINZYx[¢V*^FY\]_UpNZ[OUIR�TXÏØTXR�no]KR�P�UTIR�fQV*UXNZYx[FP�m_NbdFPrV�[FMòUXm_RaNb`adFV\v�U�Y�gtNb[FMDNb�DNeMD]FV*f2TXR�no]KR�P�UWP�Y\[¢PS|_PSUIR�`Ñs\Y�V*fQP�V*fbfZY���PrV�PXv�mKR�MD]_fbR�TrUXYY\dKUINZ`pNZÙ�RygiYxTtY��{R�T�V�fZf.PS|_PSUIR�`ádFR�T�giYxTI`#V�[FvwR�T�V*UXm_R�T�UImFV�[¥MONQP�Î)PS]_^FP�|KP�UXR�`ádFR�T�giYxTI`#V�[FvwR{�t�{|KP�UXR�`aÏfZR��{R�fhNb[DgiY\TX`#V*UXNZY\[#YxTINZsxNZ[FV�UIR�P�giTIY\`áUXm_RrYxd5R�T�V*UXNZ[_sÕP�|KP�UIR�`áV*[FM&UXm_RrNb[FMDNb�DNeMD]FV*f�dKTIYOvwR�PXP�R�P�NQPIPS]_NZ[KsMDNeP�ÎaTXR�no]KR�P�UWPw�

· ? · ?�¸ �UTVTVWSGS: R CKGSA;H R H=ºYXpG5WS<÷¡[Z=½OC_<7\ N_H;]wAB7^\ R CKGSA;HLóPIv�m_R�MD]_fbR�T�v�V*[#d_TINbY\TXNZUINbÙ�RtdFR�[FMONZ[_s�TIR�n{]_R�PSU�P(^FVxP�R�MaYx[&UImKRrPS|_PSUIR�`pÏØfbR��{R�f_Nb[DgiY\TX`#V*UXNZY\[ÕVc�xV�NZfZÏ

V*^KfZR�giY\T2R�V\v�m�TIRcno]_RcP�U���æ_Y\T2R�ÔKV*`ad_fbR{��TIR�VxM´TXR�no]KR�P�UWPqgiY\T2��m_Nev�m�V�d_d_fZNev�V*UXNZYx[ d_TXYOvwR�PXP�R�P2V*TXRy��V*NbUINZ[Ks`aNbs\mOU�TXR�vwR�Nb�{RymKNZs\m#d_TXNZYxTINZUS|{��ë�V\v�ÎDsxTIYx]_[FMa��TINbUIRtTXR�no]KR�P�UWP�dFR�TINbYOMDNQv�V*fZfb| sxR�[_R�TWV*UXR�Ma^D|pMDNQPSÎ#v�Vxv�m_RªF]FPSm�M_V�R�`aYx[FP5_�`aNbs\mOU(TXR�vwR�Nb�{RyfbY*�§d_TXNZY\TXNZUS|{�

ÜØg�V�[#V*dKd_fZNev�V*UXNZY\[ } R{� sK�Z�{V�M_V�U�V�^FV\PSR�P�UXY\T�V�s\Rt`ÕV*[FV�s\R�T��.PIv�m_R�MD]KfZR�PÖNbU�PÖY���[�TIR�n{]_R�PSU�P��oNbU2v�V�[ ]FPSRV*dKd_fZNev�V*UXNZY\[KÏ°PSd5RcvwNåjªv�NZ[DgiYxTI`#V�UINZYx[ÛMDNbTIR�vwUXfZ|{�a` ÜØg�PIv�m_R�MO]_fZNb[_s�R�[OUINZUXNZR�PtYx]_U�PSNQMDR#Y*g�UImKR&V�d_d_fbNQv�V�UINZYx[} R�� s_�b��UIm_R#MOR��DNevwR�MDTXNZ�{R�T���V*TXRaUIY)R�ÔDdKfZY\NbU�P�]Fv�m¥NZ[OgiY\TI`ÕV*UINbY\[��.V�[ÛV*d_dKTIY\dKTINQV�UIRaNb[DUXR�T�g¾VxvwR�` ]FPSUt^FRd_TXY*�ONQMOR�Mh�ãæÐYxT#TIR�n{]_R�PSU�P NePIP�]KR�MßUIm_TXY\]_sxm¼V"jFfbRúP�|KP�UXR�`���PSNZ`aNbfQV*T�NZ[OUIR�T�g¾V\v�R�P V�[FM�NZ[DgiYxTI`#V�UINZYx[_ÏP�mÐV*TINb[_s&UXR�v�m_[_NQn{]_R�P�V*TXR [KR�vwR�PXPIV*TX|�UIYàV*fZfbY�� V*dKd_fZNev�V*UXNZY\[úV�[FM�jFfbR�P�|KP�UXR�`0NZ[DgiYxTI`#V�UINbY\[�UIY)TIR�Vxv�mPIv�m_R�MO]_fZR�TWPlg¾V�TIUImKR�T�MDY���[&UXm_R�ÜWÝxÞ¼dFV�UIm��

æÖNZfbR�P�|KP�UXR�` `aR�UWV\M_V�U�Vy]_dªM_V�UIR�P } R{�âs_�b�oTXR�n{]_R�P�UWPÖs\R�[_R�T�V�UIR�M�^D|�jFfZR�vwTIRcV*UINbY\[pV*[FM�MDR�fbR�UINbY\[h�qV*[FMY\TWMDR�TXR�MÓ]_dªM_V�UIR�PtsxR�[_R�TWV*UIRcMÓ^O|&V�d_d_fbNQv�V�UINZYx[FP } R{�âs_�Z�hÞ��O��z(�yY�giUIR�[)NZ`adFY�P�R�vwR�TXU�V*Nb[�MDR�d5R�[FMDR�[Fv�NZR�P^FR�US�(R�R�[�TIR�n{]_R�PSU�Pw��æ_Y\T�R�ÔKV*`pd_fZR{�ªV&PSR�UtY�g���TINZUXR�TIR�n{]_R�PSU�Pt`#V�|#[_R�R�M�UIY)vwYx`ad_fbR�UIR�NZ[úV&v�R�TIUWV*NZ[P�Rcno]_R�[FvwR�UIYr`ÕV*NZ[OU�V�NZ[pM_V*UWV�TXR�fZNeV*^_NbfZNZUS|�Y\T�PSR�vw]_TXNZUS|rsx]FV*TWV*[OUIR�RcPw���Ov�mKR�MD]_fbR�T�P2v�V�[a]FP�R�MDR�dFR�[FMDR�[Fvw|NZ[OgiY\TI`ÕV*UINbY\[�[_Y\U2Y\[KfZ|rUXY�]_d_m_YxfQM�P�]Ðv�m�s\]FV�T�V�[DUXR�R�Pw�{^_]KU2V*feP�Y�UIY�d_TXNZY\TXNZUXNZÙ�R2TIRcno]_RcP�U�P��æ_Y\T2R�ÔKV*`pd_fZR{�TIRcno]_RcP�U�P�V�U�UIm_R�m_RcV\MÓY�gBVrfZYx[_spMDR�dFR�[FMDR�[Fvw|pv�mFV�NZ[#`aNbs\mOU(TIRcvwR�NZ�{R�m_Nbs\m_R�T�dKTINZYxTINbU�|��b�cedgf�ë,h,îji�Í6Õ*ÔyÕSáBÓ�ÑÌÍjÔgß9ètá�ã�ÒSáBÛJÕwÓ�Ï�ÛJÕwÎ�á�ÒSÛ�ÑÌÓ�ÕSÕ^ÎSÏBÔgÎ�ä�Ôg׫Ó�Õ�ã�á�áTÓ�ÒwÍ6ÛEØEÍ Ñ�Ôgß6ß6Ý�ÛJÒ�Û«Ð,ÒSÓk<«ã�Ó�ÕSÎ�ål6�Û«Ò�Ó�mTÔgÜyá�ß6ÓJÙ

Ø�Ô�Ó�Ü=Û«Ð�ÕoÜ=Í6ÖJÏ?ÎHÚBÓ�ÒSÓ�ÕwáTÛ«Ð�ÕSÍ6Ú�ß6Ó�ò|ÛJÒoÕSáBÛ?ÛJß6Í6Ð�Ö�á�ÒSÍ6Ð?ÎSÓ�ÒaÒSÓk<«ã�Ó�ÕwÎSÕ°Ù�ÕSÓ�ÐTØ?Í6Ð�Ö�áTÔ«Ñw×JÓ�ÎwÕ�ÛJã�ÎaÛgéJÓ�Ò�Ô�Ð�Ó�ÎtämÛ«ÒS×HÙGÔ�ÐTØonTã�ÕSÏ�ÍUÐ�ÖØ?Í6ÕS×yÚ�ß6Û�ÑS×=Ñ�ÔJÑwÏ�Ó�Õ°åp5q�Ï�Ó�ÑÌÛJÐTÑÀÓ�á�Î^Ûgò�íIrhìgñ°ðsf2tud�ëGíIr�vgë�ê Ü�Ôg׫Ó�Õ*Ô�á�á�ß6ÍjÑ�ÔgÎwÍUÛ«Ð?ètßUÓ�éJÓ�ß�ÒwÓk<«ã�Ó�ÕwÎ^Õ�ÑwÏ�Ó�Ø?ã�ßUÍ6Ð�Ö�ß6Ó�ÕSÕ^á�ÒSÓ�éJÔ�ßUÓ�ÐGÎ�Í6Ð�ÜyÛEØEÓ�ÒSÐÕSÝ?ÕwÎSÓ�ÜyÕ�ågq�ÏTÔgÎ�Í6Õ°ÙGÑÌã�ÒSÒSÓ�ÐGÎ�ÛJáBÓ�ÒÌÔgÎSÍ6Ð�Ö%ÕSÝ?ÕSÎwÓ�Ü=Õ�á�ÒSÓ�ÕwÓ�Ð?Î&Ô�á�á�ß6ÍjÑ�ÔgÎwÍUÛ«Ð�Õoä�Í6ÎSÏ^ÔgÐ=ÔgÚ�ÕSÎSÒÌÔJÑÌÎaéGÍ6Ó�äÛ�ò ÕwÓ�ÑÌÛJÐBØ�ÔgÒwÝ^ÕSÎSÛ«Ò�Ô�ÖJÓJÙÏ�ÍjØ?Í6Ð�Ö�ÎSÏ�Ó�Ü�Ôgá�á�Í6Ð�Ö%ÚTÓ�Îtä�Ó�Ó�Ð�éGÍ6ÒwÎSãTÔ�ß�ÔgÐTØyá�Ï?Ý?ÕSÍjÑ�Ô�ß�Ø?Ó�é?ÍjÑÌÓ�Õ�å

Page 25: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� 5

×yY{PSU�P�|KP�UXR�` TIR�fZNQV�^_NZfbNZUS|&sx]FV*TWV*[OUIR�RcP v�V�[¢V*fQPSY¥v�Y\[FPSUIT�V�NZ[üPIv�m_R�MD]_fbNZ[_sàV\vwUXNZ�ONZUXNZR�P��"æ_YxT�R�Ô_V�`aÏd_fbR{��`ÕV*[O|¥�t��Ü ÿxw�jFfbR&PS|_PSUIR�`ÕPrs\]FV�T�V*[OUIR�R&UImÐV*UpM_V*UWV�]_dªM_V�UIR�P���TINbUIUXR�[ÛUIYúUIm_R)`#V*Nb[¥`aR�`aYxTI|MDNeP�Î�v�V\v�m_Rr��NbfZf�^FR NePIPS]_R�MÓUXY)P�U�V�^_fZR�PSUIYxT�V*sxR ��NbUIm_Nb[�V sxNZ�{R�[)dFR�TINbYOM�Y�g(UXNZ`aR } R{� sK�Z��7 > PSR�vwY\[ÐM_P��W�L ^FV\v�ÎDsxTIYx]_[FM¥M_V�R�`aYx["dFR�TXNZYOMDNev�V*fbfZ|�PS�(R�R�dFPtUIm_TXY\]_sxmòUXm_RpMDNQPSÎúv�V\v�m_RpV*[FM"��TXNZUXR�P�MDNZTXU�|)^_fZYOv�ÎKPUIY8MDNeP�Ϊ�ßLyfbUIR�TX[FV*UXR�fZ|��ÖUImKRÓjFfbR&PS|_PSUIR�` vwY\]_feM¥s\R�[_R�T�V*UXR&��TXNZUIR#TXR�no]KR�P�UWPr��NZUIm :WMDR�V\MOfZNZ[KR�Pw�U<�V*[FMUImKR�PIv�m_R�MO]_fZR�T�vwYx]_fQM#s\]FV�T�V*[OUIR�R�UImFV�UtR�V\v�m&TXR�n{]_R�P�U���NZfbf�^FR�NZ[_NbUINQV�UIR�Ma^FRwgiYxTIR�UImKR�P�dFR�v�NåjFR�M)MDR�VxMDÏfZNb[_R{��ë(Y\UImÕPIvwR�[ÐV*TINbY{P2TIR�n{]_NZTXRtV�d_d_TXY\d_TXNQV*UXRtNZ[OUIR�T�g¾V\v�R�P2V*[FMaNZ[OgiY\TI`ÕV*UINbY\[_ϾP�mÐV*TINb[_s�giYxT(RwéªR�v�UINZ�{R�MONQP�ÎTIRcno]_RcP�U�PIv�m_R�MO]_fZNb[_s_�

· ? · ? · ¤�<c½_A;9�7K:�<zy§C_G9WSG9{ R CKGSA;H� Rcno]_RcP�U�d_TINbY\TINbUINbR�P PSm_Y\]KfQM�MDR�dFR�[ÐM } UIY³P�Y\`pR�MDR�sxTIR�Rx�rYx[�UIm_R�]_UXNZfbNZÙ�V�UINZYx[ÛY*g�jF[_NbUIR�PS|_PSUIR�`

TIRcP�Y\]KT�vwR�P��.P�]Fv�múV\P�`#V*Nb[&`aR�`pY\TI|ÕMDNQPSÎ�v�Vxv�m_R�^KfZYOv�Î_P���æ_Y\T�R�ÔKV*`ad_fbR{�F��TINZUXR�TIR�n{]_R�PSU�PysxR�[_R�TWV*UXR�M^FR�v�V�]FP�R�Y*g�MDNeP�Î�v�V\v�m_R�d_TIRcPIP�]KTIR } N¾� R{�b�DgiR��ãV��\V�NZfeV*^_fbR�vwfZR�V�[úv�V\v�m_R�^_fZYOv�Î_P���P�mKY\]_feM�^FR�R�ÔDdFR�MONZUIRcMh�Þ�UIm_R�TI��NQPSR{�yUXm_R8MDNQPSÎ�^_fZYOv�Χv�V\v�m_R�`#V�|¢^5RcvwY\`aRúV¥dFR�TSgiY\TI`ÕV*[FvwR�^FYxUIUIfbR�[_R�v�Î �âë(R�[_[ � 8B ¾�÷�(m_NePR�ÔKV*`adKfZR2PS]_s\sxR�P�UWPV*[äV\M_MDNbUINbY\[FV�f_PXv�m_RcMD]_fZNb[_s�Y\dKUINZ`pNZÙ�V�UINZYx[���L�U�UIm_R2`aYx`aR�[OUF��m_R�[�v�V\v�m_R2d_TIR�PXP�]_TXRT�V�NQPSR�P´UXm_R�d_TXNZY\TXNZUS|¥Y�g�P�]_^ÐP�R�n{]_R�[OU ��TXNZUXR&TIRcno]_RcP�U�P��(UImKR�TIR)`#V�|ÛV*fbTIR�VxMD|Û^5R���TXNZUXR�P´��V*NbUINZ[Ks�giYxTP�R�TI�ONQvwR{�2Ü°[#Y\TWMDR�T�UIYpno]KNQv�ÎDfb|�`#V*Î{R�PSdFV\v�RrNZ[#UXm_R�v�V\v�m_R{�_UXm_R�d_TINbY\TINbUINbR�P�Y�g2UIm_R�Y\]_UWP�UWV*[FMDNb[_sa��TXNZUIRTIRcno]_RcP�U�P�PSm_Y\]_feM"V�fQPSYÓ^FRaTWV*NeP�R�M } TIR�UXTIY{VxvwUINb�{R�fZ|F�����(m_NePrv�V�["^FRpV\v�vwYx`ad_fbNQP�mKR�MÓ^O|&]FPSNZ[_s#Nb[FMDNZTXR�vwUY\T�vwfQVxPIPSÏØ^FVxP�R�Mad_TXNZYxTINZUXNZR�P���(mFV�U�NQP��DUImKR�vwY\[OUITXY\fF^_fbYOv�ÎpV\PXP�YOvwNeV*UIRcMÕ��NbUImaRcV\v�m TXR�no]KR�P�U�v�V*[#v�Y\[OU�V*Nb[VÓdFYxNZ[OUIR�T�UIY�V�[¥R�[OUITX|�NZ[ÛV#U�V*^KfZRaY�g�TIR�n{]_R�PSU�dKTINZYxTINbUINZRcPw�#ë(|úv�mFV*[_sxNZ[_sàVÓ�xV*fb]_RaNb[¥UIm_R�d_TXNZY\TXNZUS|U�V�^_fZR��\V�[�R�[DUXNZTXR(v�fQV\PXPqY�gªTIR�n{]_R�PSU�P�v�V�[�^5RBTIR�Ïid_TXNZY\TXNZUXNZÙ�R�M } NZ[Fvwfb]FMDNb[_s�^FY\UIm�R�ÔDNeP�UINb[_s�V*[FM�P�]_^FPSR�n{]_R�[OUTIRcno]_RcP�U�P����

|�}�~ 4�� Í6ÕcÔ�ÒwÓ�ÖJÍ6ÕSÎwÓ�ÒSÓ°Ø�ÎwÒ�ÔJØEÓ�Ü�Ô�ÒS×^ã�ÕwÓ�Ø�ã�ÐTØEÓ�Ò�ß6Í ÑÀÓ�Ð�ÕSÓ òhÒSÛ«ÜFÎSÏ�Ó � ó��QáBÓ�Ð���ÛJÒwáTÛ«Ò�ÔgÎwÍ6ÛJÐ�å

Page 26: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��� ��� ö ñ>/ ¯

/0���������� ï + �2-

¯��?� $&%B')����!����t�¼MQ® ±"����® ���������2 + ���L>`aYOMOR�TI[)vwYx`ad_]_UXR�T�PS|_PSUIR�`áv�Y\[OU�V*Nb[FP�V [D]K` ^FR�TBY*gBvwYx`adFY\[_R�[DUWP(UImFV�Utv�V�[&dFY\UXR�[OUINQV�fZfb|adFV*TXÏ

UINevwNZdÐV*UIR�NZ[àPIv�m_R�MD]_fbNZ[_spV\v�UINZ�ONZUXNZR�P�� u R��DNevwR�MDTXNZ�{R�TWP(R�`�^5RcM_MDR�MaNZ[�UXm_RaÞ�Ý\�#UXT�V\MONZUINbY\[FV�fZfb|&v�Y\[OU�V*Nb[PIv�m_R�MO]_fZNb[_s#V*fbs\YxTINZUXm_`#PyUXmFV*U�]FPSR Yx[_fZ|�fbY\sxNQv�V�f�^KfZYOv�Î&[O]_` ^FR�TWPyV�[FM5Ý�Y\T�TIRcno]_RcP�UtUS|Od5RcP } N¾� R{�b�hTIR�VxMY\T���TINbUIR\�W�&�Ov�mKR�MD]_fbR�T�P;giYx]_[FM"Nb[¥NZ[OUIR�TI`aR�MONQV*UXR�vwY\[OUITXY\fZfbR�T�P } R{� sK�Z�hYx[ÛÜIÝ\ÞÚv�V*TWM_P�YxTr��NbUIm_Nb[¥PSUIY\TXÏV*sxRtR�[Fv�fZY{PS]_TIRcP��.`#V�|r]_UXNZfbNZÙ�R�VxM_MDNZUXNZYx[FV*fªmFV*TWMD��V�TIR�ϾP�dFR�vwNkjªv�NZ[DgiYxTI`#V�UINZYx[ } R{� sK�Z�\^K]FPw�KvwY\[OUITXY\fZfbR�T��{YxTMDNeP�Î8MDTINb�{R#P�UWV*UIRx���¥��VxP�UXfZ|{�`aYOMOR�TI[ÛMONQP�γMDTINb�{R�Pt��NZUIm¢VxvwUINb�{RavwYx`a`#V�[FM"n{]_R�]KR�NZ[_sàv�V*[Û]FPSRagi]_fZfÎO[_Y���fZR�MDsxR�Y*glMDNQPSÎ#vwY\[OjFs\]_TWV*UXNZY\[±�5Yxd5R�T�V*UXNZYx[��hV�[FM&PSU�V�UIR{�

u NQPSUITXNZ^_]_UXR�M&PXv�mKR�MD]_fbR�T�P�`#V*Î{R�]FP�R�Y�g(`pY\TIR�UXmFV*[�Yx[_RrR�[OUINbUS|#V*fbY\[_s#UImKR�ÜIÝ\ÞódFV�UIm�UXYaTIR�YxT�MDR�TMDNeP�ÎrTXR�n{]_R�P�UWPw���qTWV\MDNbUINZYx[FV*fªPS|_PSUIR�`#P.mFV��{R�fZNZUXUIfbR(Y\T2[_Y�PS]_d_dFY\TXU�giY\T2m_Nbs\m_ÏidFR�T�giYxTI`#V�[FvwR�MDNeP�UXTINZ^K]_UIR�MPIv�m_R�MO]_fZNb[_s_��{Nb`ad_fZR2m_Nbs\m_ÏifZR��{R�fOPIv�m_R�MD]KfZR�TWPÖvwYx]_fQM�V\vwUlV\PÖjFfZUXR�T�P�UImÐV*U2d_TINbY\TXNZUINbÙ�R2TIR�n{]_R�PSU�P�Y\T2R�[DgiYxT�vwRTIRcno]_RcP�U2MDR�d5R�[FMDR�[Fv�NZR�P�^D|�m_Y\feMDNZ[Ks�^ÐV\v�ÎrfZY���Ïid_TINbY\TXNZUS|rYxT2MDR�dFR�[FMOR�[DUlMDNQPSÎ�TIR�n{]_R�PSU�Pw���(m_NQP�MDR�s\R�[_R�TIÏV*UXR(giY\TX` Y*gqMDNQPSUITXNZ^_]_UXR�MrPXv�mKR�MD]_fbNZ[_s�fZR�V��{R�P�`�]Fv�m�UXY�^FR�MDRcP�NZTXR�Mh�xV*fbUIm_Yx]_s\maNbUÖNePÖNZ`pd_fZR�`�R�[OU�V�^_fZRYx[vw]_TXTIR�[OU�P�|KP�UIR�`#P(��NZUXm_Y\]_U�`aYOMONåjªv�V�UINbY\[&UXYaR�ÔONQPSUINZ[Ks Nb[DUXR�T�g¾VxvwR�P�V*[ÐM�d_TXY\UXYOvwY\fePw���&Y\TIRäV*sxs\TIRcPIP�Nb�{RMDNeP�UITXNZ^_]KUIR�M#PIv�m_R�MO]_fZR�TWP�TXR�no]KNZTIR�V\vwUXNZ�{R�vwY{YxT�MDNb[FV*UXNZYx[&^FR�US�(R�R�[#PIv�m_R�MD]KfZNZ[Ks�vwYx`adFY\[_R�[OU�P��

¯��g­ $&%B')����!�����)� �Ñ��� + �(��2'�® ��y]_`aR�TIY\]ÐP(P�UX]FMDNbR�P(mFV��{R�P�m_Y���[&UXmFV*U (^]Sb §J¤ Ä È R (^]wb §«¤ # R b,+ R�¦ } æ ~ æ��_�BMDNeP�Î#PXv�mKR�MD]_fbNZ[_s

TIRcP�]_fbU�PÖNb[�P�]_^FY\dKUINZ`ÕV*fOd5R�T�giY\TX`#V*[ÐvwR�giYxT2V*fbf_^_]_UUXm_R�fZNbs\mOUIR�PSUÖ�BY\TXÎDfbY{V\MKPw� É �&Y\TXR�RwéªR�vwUXNZ�{RBPIv�m_R�MD]KfZÏNZ[KsrV�fZsxY\TINbUIm_`ÕPlR�ÔDd_fbY\NbUNZ[DgiYxTI`#V�UINbY\[�V*^FYx]_U�NZ[FMONZ�ONQMD]FV�f_TIRcno]_RcP�U�P�V*[FM UXm_R�vw]_TITXR�[OU2P�UWV*UIR�Y*g.PS|_PSUIR�`vwYx`adFY\[_R�[OU�P��Ó�Ov�m_R�MO]_fZNb[_s#V*fbs\YxTINZUXm_`#P�V*TXR dÐV*TIUXNZUXNZY\[KR�M�^ÐV\P�RcM"Y\[¥��mKR�UIm_R�T�UXm_R�|�]FPSRaPXv�mKR�MD]_fbNZ[_sNZ[OgiY\TI`ÕV*UINbY\[ giTXY\` :I^FR�fbY*�=<�UImKR�PIv�m_R�MD]KfZR�T } R�� s_�b�_MDNeP�ÎpMDTINb�{RtPSU�V�UIR\�2YxT�NZ[DgiYxTI`#V�UINZYx[ giTIYx`\:WV*^FY��{R�<UImKRrPXv�mKR�MD]_fbR�T } R{� sK�Z�DTXR�n{]_R�P�U�dKTINZYxTINbUINZRcP����

LyfZUXm_Y\]Ks\m§d_TIR��ONZYx]FP#P�UX]FMDNZRcPÕdKTIY��DNeMDRúP�Yx`aR�NZ[ÐP�NZsxmDU#Nb[DUXY¥UIm_Rús\R�[_R�T�V�f�d5R�T�giY\TX`#V*[ÐvwR�^FR�mFV��DÏNZYxT#Y*g�PXv�mKR�MD]_fbNZ[_sÛV�fZsxY\TINbUIm_`ÕPw��`#V*[O|ßY�g�UXm_R�NZTÕV\PIPS]_`ad_UXNZYx[FP#V*TIRú[_YxUÓ�xV�fZNQMògiYxT&`aYOMOR�TI[�m_Nbs\m_ÏdFR�T�giYxTI`#V�[FvwR�vwYx`ad_]_UXR�T�P�|KP�UIR�`#Pw���(mKRavwYx`ad_fbR�Ô)v�mFV�T�VxvwUIR�TXNQPSUINQv�PyY*g;vw]_TITXR�[OU�MDNQPSÎúMDTINb�{R�P�v�V*[_[KY\U^FR�MD]Kd_fZNev�V*UXR�My��NZUXm�P�NZ`pd_fZR2V�[FV*fb|DUXNQv�V�f\YxTPSNZ`�]_fQV�UINZYx[t`aYOMDR�fQP�� � ]KR�` � 8� ¾�l��|D[OUIm_R�UINQv.Y\T.^5R�[Fv�mK`#V*TXÎÊ� Ë�Í6ß6Ï������XÑÀÛJÐ�ÕwÎSÒSãBÑÌÎSÕcÔ�ÕwÝ?ÐGÎwÏ�Ó�ÎwÍ ÑQä�ÛJÒw×Gß6Û?ÔJØ%ä�ÍUÎwÏ^éJÓ�ÒwÝ^Ï�Í6ÖJÏ^á�Ï?Ý?ÕSÍjÑ�Ô�ßTß6Û�Ñ�Ô�ßUÍ6ÎtÝ�ò|ÛJÒ�ä�Ï�ÍjÑSÏ;6g��6s�^á�ÒwÛgéGÍjØ?Ó�Õ�ÖJÛ?Û�Ø

áBÓ�ÒtòhÛ«ÒSÜ�ÔgÐTÑÌÓQòhÛ«ÒmÕwÛJÜyÓcÕSã�Ú�Õ�Ô�ÎSã�ÒÌÔgÎSÍ6Û«Ð Ô�ÒSÒwÍUéJÔ�ßHÒ�Ô�ÎSÓ�Õ°å

� 7

Page 27: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� 8

�(YxTIÎOfZY�V\M_P���NZUXm�P�Nb`ad_fbRÖd_TXY\^FV�^_NZfbNZUS|�MDNeP�UXTINZ^K]_UINbY\[FP5giYxTÖTXR�no]KR�P�U.PSU�V*TXUINb[_stfZYOv�V*UINbY\[FP�Y\T.TIRcno]_RcP�U�NZ[OUIR�TIÏV*TXTINb�\V�fhUXNZ`aR�P�V*TIR�]_[_TIR�d_TIR�PSR�[OU�V*UXNZ�{R�Y�g.TIR�V�fZÏi�(Y\TXfQMaPS|_PSUIR�`ÕPy� � ]KR�` � 7x�_ë�V*UXR �D� �O×yR�[_fþD � �K��v��y]�DTC{��OvwTWVBDT7_�F�h|D[Fv A 5B °� u NeP�Î#PS]_^FP�|KP�UXR�`ádFR�T�giYxTI`#V�[FvwRt`aR�UITINev�P2v�V*[K[_Y\U�Vxv�vw]_TWV*UXR�fZ|�d_TIRcMDNQvwU�UXm_R�RwéªR�vwUWPY*g�PIv�m_R�MD]_fbNZ[_sàMDR�PSNZs\[üV*[FMÛNZ`adKfZR�`�R�[{U�V�UINbY\[8v�m_YxNQvwRcPrY\[ßY��{R�TWV*fbf�P�|KP�UXR�` dFR�TSgiY\TI`ÕV*[FvwR } N°�âR{�Z��UXm_RR�feV*dFPSR�M�UXNZ`aRcPyY\T�UIm_TXY\]_sxm_d_]_U�Y*g�V*dKd_fZNev�V*UXNZY\[KÏØfbR��{R�f.U�V\PSÎ_P����èûtV�[_s � 7X ¾�a�2V\v�m¥Y�g�UImKR#P�UX]FMDNZRcP�MONQP�Ïvw]FPXP�R�Ma^FR�fbY*� P�]OéhR�T�P(giTIY\`áYx[_R�Y\T�`aY\TXRtY*g�UIm_RcP�R�NZ[FVxMDR�n{]FV\v�NZR�P��

� ? · ?�¸ ¡�:hE�<cº�9;WSGIH�J��üG°C5E�N_H;]�A(7^\ R C_GSA;H�]�7_A�\ �Ö68<�WSA�����qTWV\MDNbUINbY\[FV�f.PIv�m_R�MD]_fbNZ[_s�V�fZs\YxTINbUIm_`#P2]FP�R�mFV�T�MD��V*TXR�Ï°PSdFR�vwNåj5vyÎD[KY*��fbR�MDsxRtUIY�TXR�MD]FvwR�`aR�v�mFV*[_Nev�V*f

MDR�feV�|_P��l��Y\`aR�V*fZsxY\TXNZUImK`#Pq`pNZ[_Nb`aNkÙ�R2P�R�R�Î�UINZ`pR�Ph��m_NZfbR(YxUIm_R�TWPÖ`aNb[_NZ`aNkÙ�R�Y*�{R�T�V*fbf{dFY{P�NbUINbY\[_Nb[_s�UINZ`pR�P} N¾� R{�b��vwY\`�^_Nb[_R�MtPSR�R�Î�V*[FM�TIYxU�V*UXNZYx[FV*f_feV*UXR�[FvwNbR�P��W�Ö�&YOMOR�TI[a� ~ �oÜ�MDNQPSÎrMOTINZ�{RcPhmFV��{R�`pR�V*[�P�R�R�Î�UINZ`pR�PY*g±V�d_d_TIY�ÔONZ`#V�UIR�fb| �G> `#P } giYxTT�V�[FMDY\` MDNQPSÎ�V\v�vwRcPIP�RcP��.V�[FMr`#V*ÔONZ`�]_` } Y\T Â�` PSPFG §«¤ b Ä�ÃaR_�ªP�R�R�Î�UINZ`pR�PY*g5V*d_d_TXY�ÔDNb`#V*UXR�fZ|�5 > `#Pw�.�&YOMDR�TI[�MONQP�Î�d_fQV�UIUIR�T�P�TIY\UWV*UXR�V*U �B>T>B> � z�� Y\T.`aYxTIR{��TXR�P�]_fbUINb[_syNb[�`aR�V*[TIYxU�V�UINZYx[FV*fªfQV�UIR�[Fv�NZR�PÖY�g.V�d_d_TIY�ÔONZ`#V�UIR�fb|�8���Cr`ÕPw�.�(mD]ÐPw�D^FYxUIm#PSR�R�ÎrUXNZ`aRcPV*[FM�TIYxU�V�UINZYx[FV*fªfQV�UIR�[Fv�NZR�PmFV��{R�V�fQV�TIs\R�Nb`adFV\v�U(Y\[)`aR�V�[aTIR�n{]_R�PSU�PSR�TI�ONQvwR�UINZ`pR�Pw�

/ R�¦ ` ¡ ] £ _¢! R O £ # R�R�à � ]wÈ RÞ��{R�T�5 � |{R�V�T�PtV�s\YK� u R�[K[_NZ[_sp]FP�R�MúVaPSNZ`ad_fbR�V�[FV*fb|DUXNQv�V�fÖ`aYOMOR�fÖUXY)P�UI]ÐMD|�UIm_R�VxMD�xV*[OU�V�s\R�P�Y*g

V # ©cÄ b ¤�R�§«¤ # R�R�à ��]SÈ R (^]Sb §J¤ } �_�O��æ���d5YxfZNevw|�� u R�[_[�C A  ¾�#�(m_NQP�V*fbs\Y\TXNZUXm_`ÑV*fb��V�|_P�PIv�m_R�MD]KfZR�PUImKR dFR�[FMONZ[_s#TIRcno]_RcP�U�UImFV�U���NZfZf�NZ[Fvw]KT�UXm_RpP�`#V�fZfZRcP�U�P�R�R�Î)UINb`aRrsxNZ�{R�[�UXm_Rav�]_TITXR�[DU�MDNQPSÎúV\vwUX]FV*UXY\TdFY{PSNZUINbY\[����{Nb[FvwR�NZUrNePtNZ[DgiR�VxP�Nb^_fZR�UIY)R�Ô_VxvwUIfb|&d_TXR�MDNevwU�P�R�R�Î�UXNZ`aRcP } PSR�RaPSR�vwUXNZY\[ 5D� � � � ���PXv�mKR�MD]_fbR�T�PUS|DdKNQv�V�fZfZ|8V*dKd_TIY�ÔONZ`#V�UIR��_�O��æ ^O|Û]FP�Nb[_s¥PSR�R�΢MDNeP�U�V�[FvwR�P } N°�âR{�Z�.UIm_R)[D]K` ^FR�T�Y*gävw|OfZNZ[ÐMDR�T�PrUXY¥^FRUITWV��{R�T�PSR�M5���a�_�o��æÁTXR�MD]FvwRcP�`pR�V*[�TXR�P�dFY\[ÐP�R�UINZ`pR�PyY��{R�T�Va��NQMOR TWV*[_sxR Y�g��(Y\TXÎDfbY{VxM_Pw�p×yY��(R��{R�T���_�O��æ§NQP�V&s\TXR�R�MD|úPXv�m_RcMD]_fZNb[_s)V*fbs\Y\TXNZUXm_`�êÖUXm_R�d5YxUIR�[OUINeV*fgiY\TäP�UWV*TI�xV�UINZYx[ÛY*g�NZ[ÐMDNZ�ONQMD]ÐV*fTXR�no]KR�P�UWPNZ[ÐvwTIR�VxP�R�P���NZUXm��(YxTIÎOfZY{VxMßNZ[OUIR�[ÐP�NZUS|{�§��NZUXm �_�O��æ PXv�mKR�MD]_fbNZ[_súY*gäV¥m_R�V��O|ò�BY\TXÎDfbY{V\Mª�yVÛMDNeP�ΪçèPV\v�UI]FV�UIY\T�UIR�[FM_P�UIY�m_Y��{R�T(Y��{R�T�V�PS]_^FP�R�UyY�g2UIm_R�vw|OfZNb[FMDR�TWP�Nb[&V�[�V�UIUIR�`ad_U(UXY R�ÔDmFV�]FP�U�V�fZf�TXR�no]KR�P�UWPUIY�UXmFV*U�TXR�s\NbY\[��UXm_R�TXR�^D|úPSU�V�TI�ONZ[_sàV*[O|¥TIR�n{]_R�PSU�P�Y\]_UWP�NQMORaY*g�UImFV�UrTXR�s\NbY\[��úÜ°[¥dFV�TIUINevw]_feV*T��(�K�O��æMDNePIvwTXNZ`aNb[FV*UXR�P2V*s{V�NZ[FPSUyTXR�n{]_R�P�UWP(UIY�UIm_R�Nb[_[_R�TX`aY{PSU�V*[ÐMÕYx]_UIR�TI`aY�P�U�vw|OfZNb[FMDR�TWPw�

u R�[_[KNZ[_s8V*feP�Y¥R�ÔKV*`pNZ[_R�MúUIm_R #Q �� Y\T :IR�fbR��xV*UIYxTg<úV*fbs\Y\TXNZUXm_`��2��m_NQv�mßd_TXY��DNeMDR�PrfZY��BR�T�TIR�ÏP�dFYx[FP�RaUXNZ`aR��xV*TXNQV�[FvwR�UImÐV*[Û�_�O��æ���NZUIm�Yx[_fZ|àVa`#V*TXs\NZ[ÐV*fNb[FvwTIRcV\P�R�NZ[�UXm_R `pR�V*[)TIR�PSd5Yx[FP�R�UINb`aR} giYxTrUXm_RaPS|D[OUImKR�UINev´�BY\TIÎOfZY�V\M_P�P�UX]FMDNZRcM5���#�(m_NePrV�fZs\YxTINbUIm_`0NeP�[FV�`aR�MÓgiY\T�UIm_Rp��V�|�UImFV�UrUXm_RaMONQP�ÎV\v�UI]FV�UIY\T�PSmD]_UXUIfbR�Py^FVxv�ÎúV�[FMàgiYxTIUXm¥VxvwTIY�PIPtUIm_R�R�[DUXNZTIR�TWV*[_sxR Y�g�vw|OfZNb[FMDR�TWPw�ªP�R�TX�DNevwNZ[KsaV�fZfTXR�no]KR�P�UWPNZ[�NbU�P�dFV*UXm���Ü U�Y\[KfZ|�v�mFV�[_s\R�P�MDNZTXR�vwUINbY\[àV*UtUXm_R�NZ[_[KR�TI`aY�P�U�V�[FM�Yx]_UIR�TI`aY�P�U�vw|DfbNZ[FMOR�T�Y*gBUImKR�MDNQPSÎh�ë(R�v�V�]FP�R�� ~ Lt�ßdFVxPIPSR�PY*�{R�TÖR��{R�TI|�vw|OfZNZ[ÐMDR�T�MD]_TINb[_stR�Vxv�m�Ác© O §?R�Y�g�UXm_R�PXv�V*[��{NbUTIR�PSNQPSU�PPSU�V*TX�xV*UINbY\[`aYxTIR2RwéªR�vwUXNZ�{R�fb| } N¾� R{�b��mFV\PV�fZY��(R�T.TIRcP�dFY\[FPSRyUXNZ`aR��\V�TINeV*[FvwRx��UImFV�[a�_�O��æ(��×yY��(R��{R�T���UIm_R�MDNQPSÎ�V�TI`#PdFVxPIP�UXm_TIYx]_s\m�UImKRtvwR�[DUXR�TÖTXR�s\NbY\[�Y*g±UIm_R�MDNQPSÎ�V�U�`pY\TIR�TXR�s\]KfQV*T�NZ[OUIR�TX�\V�fQPÖUXmFV*[pUIm_R�R�MOs\R�P�� � R�no]KR�P�UWPUIY�UImKR�`pNQM_MDfbR�vw|OfZNZ[ÐMDR�T�P2UIm_R�TIRwgiYxTIR�TIR�v�R�NZ�{R�^FR�UIUXR�T�P�R�TX�DNevwR{�

�(m_Rß� ~ L��0V*fZsxY\TXNZUImK` mFVxP&V¥[O]_` ^FR�TpY*g��xV*TXNQV*UXNZYx[FPw�á�(m_R 4c¡HP ] ¡ O P #c �� V�fZsxY\TINbUIm_`}�~ ÏS� ~ Lt���(TXR�d_fQVxvwR�P�UIm_R�^_NQMONZTIRcvwUINbY\[FV�f.PIv�V�[���NZUImàVaP�Nb[_s\fbR�MDNbTIR�v�UINZYx[#Y*gBUITWVc�{R�f*� �{R�V�`�CBC? ¾�;��mKR�[UImKRtVxvwUI]FV�UIYxT(TIRcV\v�m_R�PÖUXm_RyfeV\PSU(fZYxs\Nev�V*fFv�|DfbNZ[FMDR�T��{Vygi]_fbfZϾP�UITXY\Î{R�PSR�R�Î�TIR�UI]_TX[FPNZU2UIY�UImKR;jFTWP�U�vw|DfbNZ[FMOR�T��NZUXm_Y\]KU�P�R�TX�DNevwNZ[KsaV�[D|)TIR�n{]_R�PSU�P�V*fZYx[_s#UIm_R���V�|{� ~ ÏS� ~ Lt� UXTIR�V�U�PyR�Vxv�màvw|OfZNZ[ÐMDR�T�R�n{]FV*fbfZ|#T�V�UIm_R�TUImÐV*[Óg¾V��{YxTINZ[Ks UXm_R�vwR�[OUIR�T�vw|OfZNb[FMDR�TWPw�2�(m_R � ��$� V�fZs\YxTINbUIm_`��KV*[_YxUIm_R�T�� ~ L��>�xV*TXNQV*[OU��_TXR��{R�TWP�R�P

Page 28: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���

UImKRúPIv�V�[_[_NZ[KsÛMDNZTXR�vwUXNZY\[¢��m_R�[�[_YÛdFR�[FMONZ[_s¥TXR�n{]_R�P�UWP R�ÔONQPSU Nb[ßUImKRúvw]_TITXR�[OUaMDNbTIR�v�UINZYx[ßY�grUXT�V��{R�f� �&R�TIU AE>  ¾��(m_R G � �3��� V*fbs\Y\TXNZUXm_`ávwYx` ^_Nb[_R�P ~ ÏS� ~ Lt�óV*[FM)�ÖÞ�Þt���

�qR�Y\TIR�|aV�[FM#zlNb[_Î{R�TXUIY\[�]FPSR�Ma^5YxUIm)V*[ÐV*fZ|OUINev�V*f±V*[FMpP�NZ`�]_feV*UINbY\[�`aYOMDR�fePUIY�V*[ÐV*fZ|OÙ�R�UIm_R�d5R�T�giY\TXÏ`#V�[FvwR(Y�g.PSR��{R�T�V�fFPIv�m_R�MO]_fZNb[_s�V*fbs\YxTINZUXm_`#P��\NZ[Fv�fZ]FMDNb[_s�æ ~ æ��Ð�D�_�O��æ(�O�ÖÞ�Þ���� ~ Ï°�ÖÞ�Þ�� �OV�[FM PSY\`aRmO|D^_TXNQMúV*fbs\Y\TXNZUXm_`#PtY\d_UXNZ`aNbÙ�R�M&UXY&mFV�[FMDfZRpR�ÔDUXTIR�`pR�fZ|#m_R�V��O|��(YxTIÎOfZY{VxM_P�â�qR�Y\T A 5B °�)�(m_R�NbTrPSNZ`adKfZR`aYOMDR�fQP2V\PXP�]_`aRcM V�fZNZ[KR�V*TBP�R�R�Î�vw]_TX�{R{�{Ù�R�TIY�vwYx`a`#V�[FM�V*[FMpvwY\`adKfZR�UXNZY\[�Y��{R�TXm_R�VxM_Pw�{[_Y�^_]FP(VxvwUINb�DÏNZUS|{�_]K[_NågiYxTI`afb|�MDNQPSUITINb^_]_UXR�MÓTXR�no]KR�P�U�PSU�V*TXUINb[_safZYOv�V*UINbY\[FP��hV�[FM&VpvwY\[FPSU�V�[DU�[D]K` ^FR�TBY*gBY\]_UWP�UWV*[FMDNb[_sTIRcno]_RcP�U�P } N¾� R{�b��VtvwfbY{P�RcM�`aYOMDR�fØ���.�(m_R�|rPSm_Y��(R�MrUXmFV*UB�_�O��æ&d_TXY*�ONQMOR�PqUXm_R(fbY��(R�PSUÖTXR�P�dFY\[ÐP�R�UINb`aR�P�V�UUImKR�vwY�P�U�Y*g2dFY{Y\T�P�U�V�TI�xV*UXNZYx[�TIR�PSNQP�UWV*[Fv�R{�(�(mKR�|)MDRwjF[_RcM&V�[_R��¼`aR�UITINev�giYxTyR��\V�fZ]FV�UINb[_saPXv�mKR�MD]_fbNZ[_sV*fbs\YxTINZUXm_`ádFR�T�giYxTI`#V�[FvwRrUXmFV*U�NZ[Fvwfb]FMDR�P(UXm_R�`aR�V�[)P�R�TX�DNevwR�UINZ`pR{�DUXm_R�`aR�V�[&n{]_R�]KRrUINb`aR{�KV*[FM&UXm_RTIRcP�dFY\[FPSR#UINZ`pR��\V�TINeV*[FvwR����tP�Nb[_s&UXm_NQP�`aR�UXTINQvx�qUXm_R�|úvwYx[Fvwfb]FMDR�M"UXmFV*U�UXm_Ra^FR�PSU�PIv�m_R�MO]_fZR�T�Nb`ad_fZR�Ï`aR�[OU�V�UINbY\[)P�m_Yx]_fQM�]FPSR�V#MD|O[FV*`aNev�V*fZsxY\TXNZUImK`ødFY\fbNQvw|#UImÐV*UtR�`pd_fZY�|KP��ÖÞ�Þ�� ��m_R�[�UXm_R��(YxTIÎOfZY{VxMNZ[OUIR�[FP�NbU�|�NQPfZY��üV*[FM ~ Ͼ�ÖÞ�Þ�� ��mKR�[aNZU�NQP�mKNZs\m±��(m_R�|�PS]_s\sxR�P�UXR�M#V*[�NZ`adKfZR�`aR�[OU�V*UXNZYx[r��NZUXmaPSY\`aRmO|_PSUIR�TXR�P�NeP(V*U�UImKRrv�TIY{PXP�Y��{R�T�dFY\Nb[DU�^FR�US�BR�R�[aUXm_R�V*fZsxY\TXNZUImK`#Pw�

u V*[KNZR�f±V*[FM&û�R�NQPSU2d_TIYxd5Y�P�R�M�� #c ����°/�� �_V�vwYx[DUXNZ[O]_]_` Y�g�PIv�m_R�MD]_fbNZ[_säV*fbs\Y\TXNZUXm_`#P^FR�US�(R�R�[�_�O��æ¢V*[FM��ÖÞ�Þ��¼� u V*[_NþDB7B °���(m_R � dFV�T�V*`pR�UIR�T�Nb[FMDNev�V*UXR�P(UIm_RäV*fbs\Y\TXNZUXm_`�çèP(^KNQV\P�UIY���V*T�MKPy`#V*Nb[_ÏU�V�NZ[_Nb[_s#UIm_R�v�]_TITXR�[DU�MDNZTXR�vwUINbY\[�Y�g�V\v�UI]FV�UIY\T�`aYxUINbY\[��rý�� ~ Lt� } > � > ��NQPtR�n{]_Nb�\V�fZR�[OU�UIY��_�O��æ(�±V*[FMýr� ~ L�� } � � > ��NeP�Rcno]_Nb�xV*fZR�[DUtUXY��ÖÞ�Þ����L�P�]_^FPSR�n{]_R�[OUrPSUI]FMO|"^O|�UIm_RpPIV�`aRpV*]_UXm_Y\TWP�V*UIUXR�`ad_UXR�MUIY)NQMDR�[DUXNågi|�UImKRaY\d_UXNZ`#V�f�xV*fb]_R giY\T � � û�R�NeP°D A  °�)�(m_R�|8MDR�`pY\[FPSUIT�V�UIR�M�UImÐV*U�ýr� ~ L�� } � ����NZUIm³VfZY��ã�\V�fZ]_R�Y*g � dKTIY��DNeMDR�Pt`aR�V�["TXR�P�dFYx[FP�RaUXNZ`aRcP;��NbUIm_Nb[¥VagiR�� dFR�TWvwR�[OU�Y�gt�O����æ V*[FM"TXR�P�dFYx[FP�RUINb`aRr�xV�TINQV�[FvwR�P���NZUImKNZ[8VpgiR�� dFR�T�v�R�[DU�Y*g��ÖÞ�Þ�����×yY��(R��{R�T��hUXm_R�|)]FP�R�MúP�Nb`ad_fbRrPS|D[OUImKR�UINevr�(Y\TXÎDÏfZY�V\M_P(��NbUImaR�NZUImKR�T2]_[_NågiYxTI`afb|{�\]_[KNZ`aYOM_V�fZfb|{�\Y\T�^KNZ`aYOM_V�fZfb|�MDNeP�UITXNZ^_]KUIR�M TXR�n{]_R�P�UBPSU�V*TXUINb[_s�fZYOv�V�UINbY\[FP��æ_]_TIUXm_R�TX`aY\TXR{�{UIm_R�NbT�P�Nb` ]_feV*UXY\TBvwY\[OjFs\]_TWV*UXNZY\[�`ÕV*U�v�m_R�M�UImÐV*U�TIR�dFY\TXUIR�MaNb[´�â�qR�Y\T A 5B °�

�(m_R�|pV*feP�Y�NZ`pd_fZR�`�R�[OUIR�Mrýr� ~ Lt� } � �ÖNb[#V��t�tÜ°ÿ MDR��ONQvwR�MOTINZ�{R�T�Yx[)V u � ~ z u zÏ �x� Ý AE> ��NZUXmUS�(Y � 7�8ß��ëá�O� u æ_]\ùSNbU�P�]üMDNQPS΢MDTINb�{R�Pw�§�(m_RúPS|_PSUIR�` �(YxTIÎOfZY�V\M�vwYx[FP�NeP�UIRcMòY*g�R�Nbs\mOU�Y\Ta`pY\TIR]_[_Nb�{R�T�PSNZUS|aTXR�P�R�V�T�v�m_R�TWPyMDYxNZ[_spd_TIYxs\T�V�`0MDR��{R�fZYxd_`aR�[OU��OUIR�ÔOUyRcMDNZUXNZ[_sK�hV�[FM�P�Yx`aRrUXR�ÔDU�giY\TX`#V*UXUINb[_s_��(m_R�TIR�PS]_fZUWPNZ[FMDNev�V*UXR�M�UXmFV*UBýr� ~ Lt� } > �U5o��dKTIY��DNeMDR�PÖmKNZs\mKR�T2UIm_TXY\]_sxm_d_]_U } V*[ÐM´fbY*�BR�TYxT(R�n{]_NZ�xV�fZR�[OU`aR�V�[�TIR�PSdFY\[FPSR UXNZ`aR�P��(UXmFV*[³æ ~ æ��Ð�Ö�_�O��æ(�.�ÖÞ�Þ����ÖV�[FM�ýr� ~ Lt� } > � � �����(m_R�|�vwYx[FvwfZ]ÐMDR�M�UImFV�Uýr� ~ L�� } > �65o��d_TIY��ONQMDRcP(Vrs\Y{YOM&^ÐV*fQV�[FvwRt^FR�US�BR�R�[aUXm_RtTIRcP�dFY\[FPSRrUXNZ`aR�`aRcV*[#V�[FMa�\V�TINeV*[FvwR�d5R�T�giY\TXÏ`#V�[FvwR(`pR�UITXNQv�P���LyfZUXm_Y\]Ks\m�UImKNQP2vwY\[ÐvwfZ]FPSNZYx[���V\P.TIR�VxP�Y\[ÐV*^_fbR;giYxT�dKTIR��ONZYx]FPvwYx`ad_]_UXR�TPS|_PSUIR�`ÕPw��UIm_NePMDNePIP�R�TIU�V�UINbY\[�PSm_Y���PtUImFV�UyUXm_Rrýr� ~ Lt� } � ��V*fZsxY\TXNZUImK`øMOY{R�Py[_YxUtRwéªR�vwUXNZ�{R�fb| R�ÔOd_fbY\NZU�UXm_RrYx[_Ïi^5Y�V*TWMM_V�U�V�v�V\v�m_R�P�giYx]_[FMÓNb[)vw]_TITXR�[OU�MDNeP�Î#MDTXNZ�{R�P��

�(m_R � #Q ����°���h/�� V*fbs\YxTINZUXm_`ãMDR�PXvwTINb^5RcM�Nb[3� û�R�NQP�D A V� OV*]Ks\`aR�[OU�Phý�� ~ Lt� } � �KUIY�vwY\[FPSNQMDR�T`aYxTIR�UImFV�[aùS]FP�U�UIm_R¬:�vwfbY{P�RcP�Ug<�TIR�n{]_R�PSUyNb[&R�NbUIm_R�T�MONZTIRcvwUINbY\[ÓgiTXY\`áUImKR�vw]_TXTIR�[OU�V\vwUX]FV*UXY\TtdFY{PSNZUXNZY\[±�Ü°[FP�UXR�V\Mª�ÖUImKR�V*fZsxY\TXNZUImK` vwYx`ad_]_UXR�PyUXm_R�`aR�V�[úP�R�R�ÎúMONQP�UWV*[Fv�R UXYÓUXm_RpvwfZY�P�R�PSUr� TIRcno]_RcP�U�PtNb["R�Vxv�mMDNbTIR�vwUXNZYx[���{Y_� ~ ýr� ~ L�� } � � � �hNePÖR�n{]_NZ�xV*fbR�[OUÖUXY�ý�� ~ Lt� } � �W�\ûyR�NQP�U��{R�UV�f°�b�\]FP�RcM´^FY\UXmaPSNZ`�]_fQV�UINbY\[V*[ÐM�V\vwUX]FV*f.NZ`adKfZR�`aR�[OU�V*UXNZYx[aUIYaUXR�P�U�UImKRrdFR�T�giYxTI`#V�[FvwR�Y*g ~ ýr� ~ Lt� } ��� � �ÖgiY\T��\V�TINbY\]FPt�ãV*[FM ��xV*fb]_R�Pw�à�tP�Nb[_s#UIm_R#PXV*`aRpP�Nb` ]KfQV*UXY\T�vwYx[DjFs\]KT�V*UXNZYx[ßVxPrNZ[ � û�R�NeP°D A  °�.UIm_R�|8MDR�UXR�TI`pNZ[_R�M#UIm_Rp`aR�V*[V*[ÐM&P�UWV*[FMKV*T�M)MDR��ONQV�UINZYx[agiY\T�TIRcno]_RcP�U�n{]_R�]_R�V�[FM&PSR�TI�ONQv�RtUINb`aR�Pw��ýBV*fb]_R�P(Y�g2�¼s\TXR�V*UXR�T�UImÐV*[&]K[_NZUS|MDNeM�[_YxU�d_TIY��ONQMDR�PSNZs\[KNåjªv�V�[DU�Nb`ad_TIY��{R�`�R�[{U(giYxT ~ ýr� ~ L�� } �r� � �W�F�(m_R�|úV�fQP�YàvwY\`pdFV*TXR�M�PIv�m_R�MD]KfZÏNZ[Ks�V*fbs\YxTINZUXm_`#P�^D|úVxvwUI]FV�f�NZ`adKfZR�`�Rw[OU�V�UINbY\[úV*[ÐMòMOR�UIR�TX`aNZ[KR�MÓUXmFV*Ua�_�o��æ d_TIY��ONQMDRcP�UImKRam_NZsxm_R�PSUUImKTIY\]Ks\m_d_]KU�V*[FM NeP�UXm_Rt`aY�P�UBP�]FPXvwR�d_UXNZ^_fbR�UIY�TIR�n{]_R�PSU�P�UWV*TX�\V�UINbY\[��2�ÖÞ�Þ��¼NQP�UXm_RtfbR�V\PSU(PS]FPIv�R�d_UINb^_fZRV*[ÐMrd_TIY��ONQMDR�P � C � Y*gªUIm_RBUIm_TXY\]_sxm_d_]_U2Y�g��_�O��æ(��ý2R�T�PSNZYx[FPqY�gªýr� ~ Lt� } � �ªV�[FM ~ ýr� ~ L�� } �r� � �ªV�fZfd_TXY*�ONQMOR�d5R�T�giY\TX`#V*[ÐvwR�TIYx]_s\m_fb|�R�n{]_NZ�xV*fbR�[OUÖUXYrUImÐV*U2Y*gq�ÖÞ�Þ����O�(m_R�NbT2P�UX]FMD|�g¾V*NZfbR�MrUIY�MDR�`aY\[FPSUITWV*UIRV*[O|#PSNZs\[KNåjªv�V�[DU�VxMD�xV*[OU�V�s\RrY�gR�NZUImKR�T(ýr� ~ Lt� } � �YxT ~ ýr� ~ Lt� } �r� � ��Y*�{R�T(UImKRt`aY\TXRtUITWV\MDNbUINbY\[FV�f

Page 29: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� C

PIv�m_R�MO]_fZNb[_s�V*fbs\Y\TXNZUXm_`#Pw��Ü°[�VxM_MDNbUINZYx[��FUIm_R�^5R�[Fv�mK`#V*TXÎa�(YxTIÎOfZY{VxM&��VxP;m_RcVc�ONZfb|a�(R�NZs\mOUIRcMÕUXY���V*TWM_PTIRcV\M¥TIR�n{]_R�PSU�PtgiY\TrjFfbRaPS|_PSUIR�` MDNZTXR�vwUXY\TI|ú^_fbYOv�ÎKPrvwfb]FP�UXR�TIRcM¥V*TXY\]_[FMÛVÓgiR�� dFYxNZ[OU�PrNZ[8UIm_R#fZYxs\Nev�V*fP�dÐV\vwR{�BLtP(`aYOMOR�TI[#Y\dFR�TWV*UXNZ[_spP�|KP�UXR�`#P�US|Od_NQv�V*fZfb|av�V\v�m_RygiTIRcno]_R�[DUXfZ|pV\v�vwRcPIP�RcMÓMONZTIRcvwUIYxTI|�^_fZYOv�Î_P(Nb[`#V�NZ[a`aR�`aY\TX|{�\UImKNQP(�(YxTIÎOfZY�V\MÓ��V\P�n{]_NZUXR�]_[_TIRcV*fZNeP�UXNQv\�

�K#Q ����°/�� �{YxT ��] £Q¦cÄHÆ #c �� �{TXR�d_TIRcP�R�[OU�PV�PSfZNZsxmDUXfZ|äMDNåéªR�TXR�[DUlvwY\[OUINb[D]_]K` Y*gqPIv�m_R�MD]KfZÏNZ[KsaV�fZs\YxTINbUIm_`#P(^FR�US�BR�R�[��_�O��æ¢V*[FM)�ÖÞ�Þ��¼�è�{]_s\s �B>  ¾�(�¼� ~ Lt� } � �2R�` ]_feV*UXR�PUIm_Rä�ÖÞ�Þ�� V�fZs\YxÏTINbUIm_` ��m_NZfbR�d_]_fbfZNZ[Ks#VN:WP�R�TX�DNevwRr��Nb[FMDY��=<&V�fZY\[Ks&^FR�m_Nb[FMh���(m_R � dFV�T�V*`pR�UIR�T�NZ[FMDNev�V*UXR�PyUXm_RaPSNZÙ�RY*g�UIm_R�PSR�TI�ONQv�R���Nb[FMDY����r��m_R�[�UIm_R�V�fZs\YxTINbUIm_`�PIv�m_R�MD]_fbR�PyTXR�no]KR�P�UWPy��NZUXm_NZ[)UIm_R���Nb[FMDY�����[_R�NZUXm_R�TUImKR4:Wvw]_TXTIR�[OUg<�MDNZTXR�vwUINbY\[aY�gUXT�V��{R�fF[_YxTyUXm_Rt��NZ[ÐMDY�� ^FY\]K[FM_V*TXNZR�P�v�mFV*[_sxR{��¼� ~ Lt� } > � > ��NQP(R�n{]_NZ�OÏV*fbR�[OUrUIYà�ÖÞ�Þt����V*[FM¥�¼� ~ Lt� } � � > ��NQP�Rcno]_Nb�xV*fZR�[DU�UIYú�_�O��æ(�(��]_s\s�Pr]FP�R�MúUIm_R#PXV*`aRÕP�NZ`�]_feV*UIYxTV\P¬� û�R�NeP°D A  (UXY¥MOR�UIR�TX`aNZ[KR�UImFV�U �¼� ~ L�� } � ��dFR�T�giYxTI`#P�^5RcP�U���NZUXm¢V��xV*fb]_R#Y*g � ^FR�US�(R�R�[ > � >D�V*[ÐM > � > 7D�p×yRpMDR�`aYx[FP�UXT�V*UXR�M&UImÐV*U�giYxT�P�R��{R�TWV*f�{R�TI|�PSm_Y\TXU�PSR�no]KR�[FvwR�P�Y*g�TIRcno]_RcP�U�P����¼� ~ Lt� } � �d_TXY*�ONQMOR�PÖV�`aR�V*[äP�R�R�Î�UXNZ`aRBvwfbY{PSR�TÖUXY:IYxd_UINb`#V*fþ<;UXmFV*[#�_�O��æB�o� ~ L��r�\V�[FM�ýr� ~ Lt� } > �U5o���.�tPSNZ[_s�VPIv�m_R�MO]_fZR�T2Nb`ad_fZR�` R�[OU�V�UINbY\[�V*[ÐMÕ�BY\TXÎDfbY{V\M#PSNZ`aNbfQV*T2UXY�� û�R�NeP°D A VB °�Om_R�PSm_Y��(R�MaUImÐV*U��¼� ~ Lt� } > � > 5{�d_TXY*�ONQMOR�P�V � 5O�6D � TXR�MD]FvwUXNZYx[ÓNb[#`aR�V*[pTIR�PSd5Yx[FP�R�UINb`aRyY��{R�TBýr� ~ Lt� } > �U5o�W�

�(m_R��¼� ~ Lt� } � ��V�fZs\YxTINbUIm_`�P�m_Y���Py`aYxTIR�d_TIYx`aNQPSR�UXmFV*[�ý�� ~ Lt� } � �2giY\TtmKNZs\mKÏØdFR�TSgiY\TI`ÕV*[FvwRMDNeP�Î�TIR�n{]_R�PSU(PXv�mKR�MD]_fbNZ[_sK�DVxP�NbU(��NZfbfFUIR�`adFYxT�V*TXNZfb|�:IUX]_TI[ÕV*TIYx]_[FMo<�V*[ÐMaP�R�TX�DNevwR�P�R�n{]_R�[OUINeV*f_TXR�no]KR�P�UWPNZ[8fZY\sxNQv�V�fZfb|¥VxPIvwR�[ÐMDNZ[_s�YxT�MDR�T } MD]_TXNZ[_s�NbU�P�MDR�PIv�R�[FMDNb[_s�d_mFVxP�R\�W�"ýr� ~ L�� } � �t[_R��{R�T�TIR��{R�TWP�R�P�MDNZÏTIRcvwUINbY\[Û]_[_fbR�PIP�UIm_R�TIR�V�TIR)[_Y"TXR�n{]_R�P�UWP´��NbUIm_Nb[ÛUIm_R)[_R�V*TXR�P�U�j_giUXmßY*g�UIm_R)fZY\sxNQv�V�f�P�dFVxvwR-:X^FR�fZY��=<UImKRúvw]_TITXR�[OU fbYOv�V*UXNZY\[±� Ly[FMß��m_R�[�NZU#MDY{RcPÕUX]_TI[§V�TIYx]_[FMh��NZU#MDY{RcPÓPSYÛd5R�TI`#V�[_R�[OUIfZ|��¼�(mFV�UÓNePw�NZUÕv�mFV�[_s\RcP´giTIYx` UIm_RúMDRcPIvwR�[ÐMDNZ[_s8d_mFV\PSR�UIYÛUImKRúV\PIv�R�[FMDNb[_sÛd_mFV\PSR{� �ÔOd5R�TINZ`pR�[DUWPrNZ[�UXm_NQPaMONQP�ÏP�R�TIU�V�UINbY\[ÛMDR�`aY\[FPSUITWV*UIR�UXmFV*U�UIm_NePt^5R�mFV��DNbY\T�v�V*]ÐP�R�P�P�NZsx[_Nåj5v�V*[OUtdFR�T�giYxTI`#V�[FvwRpMDR�sxT�V\MKV*UINbY\[¥��mKR�[PIv�m_R�MO]_fZNb[_s�PSR�no]KR�[DUXNQV�f(TIRcno]_RcP�U�PtgiY\T�MDNeP�ÎKPr��NZUXmòdKTIRwgiR�UWv�mKNZ[_s)Y\[_Ïi^FY{V*TWMßv�Vxv�mKR�Pw�8�y[DgiY\TXUI]_[ÐV*UIR�fZ|{�UImKR��¼� ~ Lt� } � �BV*fbs\YxTINZUXm_`÷NeP([_Y\U�P�UX]FMDNZRcMÕNb[aUImKNQP�MDNQPXP�R�TXU�V*UXNZYx[��

I�#c ����°/�� �FVrUIR�`pd5YxT�V�f5�xV�TINQV�UINbY\[#Y*g��¼� ~ Lt� } � �W�{]_dªM_V*UXR�P;UXm_R:Wvw]_TITXR�[OUg<rm_R�VxM dFY{PSNZUINbY\[V*U�UImKR&v�Y\`ad_fbR�UINbY\[úY*g�RcV\v�mòTXR�n{]_R�P�U�TWV*UXm_R�T�UImÐV*[ßUXm_R&Nb[_NZUXNQV�UINZYx[Z� û�R�NeP �x�  °�¢�(mFV�U NePw�BV�TXR�no]KR�P�UV*TXTINb�DNb[_s�V�U(UImKR�PIv�m_R�MD]KfZR�T`ÕVc|�^FR�v�m_Y�P�R�[#VxP�UXm_Rt[_R�ÔOU2UIY�TXR�vwR�Nb�{R�P�R�TI�ONQvwR�Någ±NZU(NeP�:�vwfbY{P�RcP�Ug<rUXYrUXm_RdFY{PSNZUINbY\[�Y�g(UXm_RrfeV\PSUtTIR�n{]_R�PSUtv�Y\`ad_fbR�UIRcM } N¾� R{�b�_[_Y\UtUXm_RrTXR�n{]_R�P�U�vw]_TXTIR�[OUIfb|a^FR�NZ[KsaPSR�TI�ONQvwRcM5�����(m_NePV*fbs\YxTINZUXm_`�s\NZ�{RcPldKTINZYxTINbU�|�UXYrfbY\s\Nev�V*fbfZ|�PSR�no]KR�[DUXNQV�f } YxT([_R�V�TIfb|aPSR�no]KR�[DUXNQV�fØ�.PSUITIRcV*`#PY*g�PS|D[Ðv�m_TXY\[_Yx]FPTIRcno]_RcP�U�Pr��mKR�[ßUXm_R�vwYx`ad_]_UXRaUINb`aRa^FR�US�(R�R�[ÛTIR�n{]_R�PSU�vwY\`adKfZR�UXNZY\[ÐPrV*[ÐMßP�]K^FP�R�n{]_R�[OU�NZ[_NbUINQV�UINbY\[FPNQP�P�`#V�fZf°��û�R�NQPSU�V*[ÐM��úR�P�UWV*fbfR�ÔKV*`aNb[_R�MaUIm_R�dFR�TSgiY\TX`#V*[Fv�R�Y*g�æ ~ æ��F�F�¼� ~ Lt� } � ����V�[FM"VaTXR�V\MDÏd_TXNZY\TXNZUXNZÙ�R�M��{R�TWP�NZYx[aY*g ~ Ͼ�ÖÞ�Þ�� ]FPSNZ[_s�V�PS|D[OUImKR�UINevy�hNb[D]_Ô�jFfbR�P�|KP�UXR�` �BY\TXÎDfbY{V\Mª�(�(m_NeP(�(YxTIÎOfZY{VxM��VxP V�fZ`aY�P�U�dFV*UXm_Y\fbY\s\Nev�V*fbfZ|Û�(YxT�PSUIϾv�V\PSRÓgiY\T�UXm_R ~ Ͼ�ÖÞ�Þ��0V*fZsxY\TXNZUImK`��2V*U�fZR�VxP�U�dFV�TIUXNQV*fbfZ|úNZ[O�xV*fZÏNQMKV*UINb[_s¥UXm_R&TXR�P�]_fbU�P�Y*g�UImKR�NZTpP�UX]FMD|{� �(m_R&jFfZRàP�|KP�UXR�` �(Y\TXÎDfbY{VxM�vwY\[FPSNQPSUIR�MßY�grR�NZs\mOU�d_TXYOvwR�PIPSR�PNQPXP�]_Nb[_s)P�|O[Fv�m_TIYx[_Y\]FP�P�Nb[_s\fbR�Ï°PSR�vwUXY\T�TIR�VxM�TXR�n{]_R�P�UWPtUIY#R�NZsxmDU�:SjFfZR�P�<aNZ[úUIm_RpP�|O[DUXm_R�UXNQv��BY\TXÎ_PSdFV\vwR���2V\v�m"dKTIYOvwR�PXP�v�m_Y�P�R�V#[_R��¼jFfZR�UXY#TIR�VxM"V�giUIR�T�TIRcV\MDNb[_s#UIm_R�feV\P�U�^_fbYOv�Î)Y*g�UIm_R�d_TIR��DNbY\]FP;jÐfZR{��æ_YxTV ~ Ͼ�ÖÞ�Þ��0PXv�m_RcMD]_fZR�T�V*[ÐMßV�8\ϾP�R�s\`aR�[OU�MKV*U�Vúv�Vxv�m_R��2P�]Fv�m¢V&�(Y\TXÎDfbY{VxM³TXR�P�]KfZU�PrNb[¢V&�{R�TI|úfZY��v�Vxv�m_R�m_NbU�TWV*UXR{�2�(m_R�PIv�m_R�MD]_fbR�T2PSR�TI�ONQvwRcPlYx[_RtTXR�no]KR�P�UgiTIYx` R�V\v�m�d_TIYOvwRcPIP(MO]_TINb[_srR�Vxv�mpPIv�V*[#VxvwTIY�PIPUImKR�fZY\sxNQv�V�fPSdFV\v�R{����mKR�[��¼� ~ Lt� } � �BY\T�ÿr� ~ Lt� } � �BNQP�]FP�R�M&UXY#PIv�m_R�MO]_fZR�UIm_NePy�(YxTIÎOfZY{VxMh�hUXm_RV\v�UI]FV�UIY\T�Y*giUXR�[ÛV*fbUIR�TX[FV*UXR�Pt^FR�US�(R�R�[#ùS]FPSU�US�BYÓjFfbR�P } N°�âR{�Z�ªU��BY)vw|DfbNZ[FMOR�T�P���]_[OUINZf�Y\[_RaYxTrUXm_R YxUIm_R�TmFVxP�^FR�R�[pvwY\`pd_fZR�UXR�fZ|�TIR�VxMh�2Ü°[ UXm_NQP2PIv�R�[FV*TXNZYK�oUXm_R�V*]_UXY\`#V�UINQv�d_TXRwgiR�U�v�m_Nb[_st`aR�v�mFV�[_NQPS`>Y�g�UXm_RtMONQP�Îd_TXY*�ONQMOR�P(V�` ]Ðv�m�m_NZsxm_R�T�v�V\v�m_R�m_NZUBT�V�UIRV� Vrm_NZU�TWV*UXR�Y�gY��{R�T �B>H� NeP�TXR�dFY\TIUXR�Mh��û�NZ�{R�[aUXm_RtdFY{Y\Tv�m_Y\NevwR Y�g��(YxTIÎOfZY{VxM"NZ[ � û�R�NQP �\�  °�ÖNbU�NQP�]K[FvwfZRcV*Tr��mÐV*U�VxMD�xV*[OU�V�s\R } Nkg�V*[O|5��ÿr� ~ L�� } � ��mFV\PrY��{R�T�¼� ~ Lt� } � �2Y\T�V*[O|aYxUIm_R�T�PIv�m_R�MO]_fZNb[_s�V�fZs\YxTINbUIm_`��

Page 30: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��A

/ R�¦ ` ¡ ] £ _¢! R O £ 2 Ä�§ ] ¤ ] Ä�£ ] £ _¢��]SÈ Rû�NZ�{R�[äMDR�U�V�NZfbR�MrMDNeP�Î�vwYx[DjFs\]KT�V*UXNZYx[aV�[FM PSU�V�UIR�NZ[OgiY\TI`ÕV*UINbY\[��xVtPXv�m_RcMD]_fZR�Tv�V�[�v�mKY{Y{P�R�UXm_R(dFR�[ÐMDÏ

NZ[Ks&TIRcno]_RcP�U�UImFV�Ur��NbfZfNb[Fvw]_T�UIm_R�`aNZ[KNZ`�]_`ádFY{PSNZUINbY\[_Nb[_s&UXNZ`aR��Õ��R��{R�T�V�fBP�UI]ÐMDNZR�PtmFV��{R�R�ÔKV*`aNb[_R�MUImKRrdFR�T�giYxTI`#V�[FvwR�Y*g�P�]Fv�m�VaPXv�mKR�MD]_fbNZ[_s�V�fZs\YxTINbUIm_`�� u R�[_YxUIR�M�VxP # ©QÄ b ¤�R�§«¤ � ]wÈ R (^]wb §«¤ } �O��æ2�NZ[ �è�{R�fZU �B>  .V*[ÐM # ©cÄ b ¤�R�§«¤ � ¡H¡HR�§?§ � ]wÈ R (^]Sb §«¤ } �OL2��æ���NZ[ � �{VxvwY �O�  °�DUXm_R�UIR�TX` # ©cÄ b ¤�R�§«¤ 2 ÄsG§ ] ¤ ] Äa£ ] £ _0� ]wÈ R (^]Sb §«¤ } �Oz2��æ��rNeP´]ÐP�R�MÛNZ[ßUXm_NQP��(YxTIÎÛUIY³vwfQV�TINågi|8UIm_R)R�Ô_VxvwU�d_]_TIdFY�P�R�Y*g�UIm_NePV*fbs\YxTINZUXm_`��a�{R�fbUIÙ�R�T���R�U�V*f¾�Z�.P�Nb` ]_feV*UXR�M&V)MDNQPSÎúP�]_^FPS|_PSUIR�`0��NbUIm8V&vwYx[FP�UWV*[OU�[D]_`�^FR�TtY�g�d5R�[FMDNZ[KsTIRcno]_RcP�U�P } ]KdßUIY �?>T>B> ���¼�{VxvwY\^ÐP�Y\[ V*[ÐMò��NZfbÎ{R�P�P�Nb` ]KfQV*UXR�M¥VúMDNQPS΢P�]_^FPS|_PSUIR�` ��NbUIm�VúzÖYxNQPIPSY\[V*TXTINb�\V�fhd_TXYOvwR�PXPlgiY\TBTIR�n{]_R�PSU�P��ë(Y\UXm#P�UX]FMDNbR�P�]FPSR�M �BY\TIÎOfZY�V\M_P2��NZUXma]_[_NkgiY\TI`pfZ|�MONQP�UXTINb^_]_UIRcM´TXR�no]KR�P�UP�UWV*TXUINZ[Ks fbYOv�V*UXNZY\[ÐPw�

�(m_R)MDNQPSÎ¥]_UXNZfZNbÙ�V*UXNZYx["[O]_`�^5R�T�P�dKTIR�PSR�[DUXR�M"Nb[Z� �{R�fZU �T>  �Nb[FMDNQv�V*UIRpUImFV�Ua�Oz2��æ dKTIY��DNeMDR�Pr]_dÛUXYC >H� m_NZsxm_R�T�dFR�T�giYxTI`#V�[FvwR�UXmFV*[ ~ Ï°�ÖÞ�Þ��÷Y\T��_�O��æ�giY\T�UIm_R�mKR�V��DNbR�P�Ut�BY\TXÎDfbY{V\MKPw�aL�UtUXm_RaPXV*`aRUINb`aR{�_UXm_R�TIR�n{]_R�PSUyTXR�P�dFYx[FP�R�UINb`aR��\V�TINeV*[FvwRrgiYxTr�Oz2��æ } VasxTIR�R�MO|&V�fZsxY\TINbUIm_`)�(TXNQP�RcPtMDT�V�`#V*UXNQv�V�fZfb|��NZUXm¥NZ[ÐvwTIR�VxP�Nb[_s#�(Y\TXÎDfbY{VxM"NZ[OUIR�[ÐP�NZUS|{�p�(m_Ra`#V�ÔDNb`�]_`áTIR�PSdFY\[FPSRaUINb`aR�Y\^FPSR�TI�{RcMàgiYxT �Oz2��æ¼V�U�Vn{]_R�]_RBfZR�[_sxUIm�Y*g �?>T>B> NQP�8_� � UINb`aR�Phm_Nbs\m_R�T.UImÐV*[�UImÐV*UY�g ~ Ͼ�ÖÞ�Þ��ÁYxT(�_�O��æ(���{V\vwYx^FP�Yx[�V*[FMr��NbfZÎ{R�PP�mKY*�BR�MaUImFV�Uy�Oz2��æÛPIV�UI]_TWV*UXR�P;UXm_R�PSUI]FMDNbR�MaMDNeP�ÎpP�]_^ÐP�|KP�UIR�`áV*U�V�[&V�TITXNZ�xV*fªT�V*UXRtY*glV*dKd_TIY�ÔONZ`#V�UIR�fb|A�> TIR�n{]_R�PSU�P(dFR�T�P�R�vwYx[FMh�ªV\P�vwY\`pdFV*TXR�MaUIY �B> TXR�no]KR�P�UWP(d5R�TtPSR�vwY\[ÐMÕgiY\T�ýr� ~ Lt� } > �U5o�BV*[ÐM��_�O��æB��(m_R�PSR�US�(Y�P�UX]FMDNZRcPÖ]FP�RcMr^5R�UIUIR�T2MDNQPSÎ�MDTXNZ�{RB`aYOMDR�fePÖUImFV�[ UXm_Y{PSR�]FP�RcM´Nb[�d_TIR��ONZYx]FPPSNZ`�]_fQV�UINZYx[�P�UI]ÐMDÏNZRcP;Y�g�PXv�mKR�MD]_fbNZ[_spV*fbs\Y\TXNZUXm_`#Pw��×�Y*�BR��{R�T��_UIm_R�|)V�fQP�Yp]FP�R�M&]K[_TIR�V�fZNeP�UINev��BY\TIÎOfZY�V\M_P���NZUImúPSNZ`adKfZNQPSUINevm_Y�P�U�`aYOMDR�fePw�

# R�¡B¤�Ä b G�� #c ����°/�� ��V��\V�TINeV*UINbY\[úY\[úýr� ~ Lt� } � ���ªV*fQPSY#U�V*Î{RcPyTIYxU�V*UXNZYx[FV*f2fQV�UIR�[Ðvw|&Nb[DUXY#V\vwÏvwYx]_[DU�� � R�|O[�DBD? °�)�(m_R � dFV�T�V*`pR�UIR�T�NZ[FMDNev�V*UXR�PtUIm_RÕV*fZsxY\TXNZUImK`�çèPt^_NeV\P�UXY���V*TWM_P�`ÕV*NZ[OU�V�NZ[_Nb[_saUXm_Rvw]_TXTIR�[OU�MONZTIRcvwUINbY\[#Y*glV\vwUX]FV*UXY\T�`aY\UXNZYx[�� � R�|O[_Y\feM_P�P�m_Y��BR�MaUImFV�U��{RcvwUIYxTIÏiýr� ~ Lt� } � ��d_TIY��ONQMDRcP(]_dUIYúV �X� NZ`ad_TXY��{R�` R�[OUtNZ[Û`aR�V�[¥TIRcP�dFY\[FPSR#UINZ`pR Y��{R�T�ýr� ~ Lt� } � ��giY\T�VúP�|O[DUXm_R�UXNQvrjFfZR#PS|_PSUIR�`�(YxTIÎOfZY�V\Mh�

ë(|)MDR�UIRcvwUINb[_s�V*[FM�PXv�mKR�MD]_fbNZ[_s�PSR�no]KR�[DUXNQV�f.P�UITXR�V*`ÕP(Y*g2TXR�no]KR�P�UWP;Nb[&fZYxs\Nev�V*fbfZ|#VxPIvwR�[ÐMDNZ[_s�Y\TWMDR�T��`aY�P�UtY�g�UImKR�V*fZsxY\TXNZUImK`#PyMOR�PIvwTXNZ^FR�M&Nb["UXm_NQPtv�mFV�d_UIR�T�v�V*[ú^FR�`aYOMDNåjÐR�M&UIYagi]_TXUIm_R�T�TIR�MD]ÐvwR�PSR�TI�ONQvwRUINb`aR�P�� û�NZ�{R�[�UXmFV*U�fZY\sxNQv�V�fZfb|�P�Rcno]_R�[DUXNQV*f�^_fZYOv�Î_P�U�|Od_Nev�V*fbfZ|&`ÕV*d�UIY#d_mO|KP�NQv�V*fZfb|�PSR�no]KR�[DUXNQV�f`aR�MDNeVfZYOv�V*UINbY\[FP��FP�R�n{]_R�[OUINeV*fªTIR�VxMÕTXR�n{]_R�P�UWP } V*[FM#��TINZUXRtTIRcno]_RcP�U�P(Nb[#P�Yx`aR�v�VxP�R�P��2NZ[Fv�]_T�Ù�R�TXYrdFY{PSNZUINbY\[_Nb[_sMDR�feV�|_P���m_R�[¢P�R�TX�DNevwR�M�NZ[ÛfZYxs\Nev�V*fbfZ|úV\PXvwR�[FMONZ[_s�YxT�MDR�T��¥LáPIv�m_R�MO]_fZR�T�R�ÔOUIR�TI[FV�f(UIY�UXm_R)MDNQPSÎ¥MOTINZ�{RV*feP�Y)mFV\PtUImKR Yxd_UINbY\[¥Y�g=¡HÄ�£Q¡ O ¤�R�£ O ¤ ] £ _ } vwY\`�^_NZ[KNZ[_sO��PSR�no]KR�[DUXNQV�fTIR�n{]_R�PSU�PtNZ[OUIYÕV&P�Nb[_s\fbR�fQV�TIs\R�TTIRcno]_RcP�U��)L÷vwYx[Fv�V�UIR�[FV�UIR�MúTIR�n{]_R�PSUrNZ[Ðvw]_T�P�fZR�PXP�UXY\U�V�f(d_TXYOvwR�PXP�NZ[KsúV*[FM¥d_TXY\UIYOv�Y\f�Y��{R�TImKR�V\M_PtUXmFV*[�(Yx]_fQM&UXm_R�PSR�U�Y*g�vwY\[OUITXNZ^_]KUINZ[Ks TXR�no]KR�P�UWPw��Þ�[)UIm_R�YxUIm_R�T�mFV�[FMh�h[_Yx[_R�Y*gBUXm_RrNb[FMDNZ�ONQMO]FV*f�TXR�no]KR�P�UWP:�v�Y\`ad_fbR�UIRE<´]_[OUINbfUImKR R�[OUINbTIR�vwYx[Fv�V�UIR�[FV�UIR�M�TIRcno]_RcP�U�vwYx`ad_fbR�UIR�P����(m_NeP�`ÕVc|)V�TIUINkjªvwNeV*fZfb|&Nb[FvwTIRcV\P�RUImKRrPSR�TI�ONQv�RtUINb`aR�PÖgiY\T�P�Yx`aRtY*g�UImKRrv�Y\[OUITINb^_]_UXNZ[_s�TXR�no]KR�P�UWPw�

� ? · ? · ¡�:hE�<cº�9;WSGIH�J��üG°C5E�N_H;]�A(7^\ R C_GSA;H�]�7_A�\ ���U rAc¿(<���(m_NQP�P�RcvwUINbY\[ÛMDRcPIvwTXNZ^FR�P�PIv�m_R�MO]_fZNb[_súV*fbs\Y\TXNZUXm_`#P�UXmFV*U�]_UXNZfZNbÙ�RpP�|KP�UIR�`aÏØfbR��{R�fNb[DgiY\TX`#V*UXNZYx[ } PSR�R

P�RcvwUINbY\[35D�65{�.UIY�Vxv�mKNZR��{RBd5R�T�giY\TX`#V*[ÐvwR�V*[FM�TIR�fbNQV*^KNZfZNbUS|�sxY{V�fQPw�2Ü°[�UIm_R�V*^ÐP�R�[Fv�RyY�g�P�]Fv�m Nb[DgiY\TX`#V*UXNZYx[��VaPXv�m_RcMD]_fZR�T�v�V*[_[KY\U�NQMDR�[OUINkgi|´:ImKNZs\m�dKTINZYxTINbU�|Ç<rTIRcno]_RcP�U�P���×yY��(R��{R�T��DNbUtv�V�[�vwYx[DUXTIYxfÖTXR�P�dFY\[ÐP�R�UINb`aR�xV*TXNQV*[ÐvwR�V*[FM#UIm_R�TXR�^O| TXR�MD]FvwR�UIm_R�dFY{PXP�NZ^KNZfZNbUS|aY*glP�UWV*TI�ONZ[Ks m_Nbs\m#d_TXNZY\TXNZUS|�TIR�n{]_R�PSU�Pw�

Page 31: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� D

/ R�¦ ` ¡ ] £ _¢/ R�§?Á�Äa£c§?R ��]SÈ R¡� Oob�]wO £Q¡HR�&Y{PSU Y�g�UIm_RàV*fbs\Y\TXNZUXm_`#PrMOR�PIvwTXNZ^FR�MÛNZ[¢P�R�v�UINZYx[�7D�65O� � v�V*[¢^FR&`aYOMDNkjFR�M"UXY"TXR�MD]Fv�RÓTXR�P�dFYx[FP�R

UINb`aRt�xV*TXNQV�[FvwR{�B�(m_RrTXR�P�]KfZUINb[_s�V*fbs\YxTINZUXm_`#P�V�TIR�v�fQV\PXP�NkjFR�M&VxP;R�NZUImKR�T�3 O ¤�¡�©³YxT OÇ_a] £ _ V*fZsxY\TXNZUImK`#Pw�ë�V*UWv�màV*fbs\Y\TXNZUXm_`#P�P�R�TX�DNevwR�VÓPS]_^FPSR�UtY*gBUXm_RrdFR�[FMONZ[_saTXR�n{]_R�P�UWPw��PSR�fZRcvwUIR�Ma^O|)P�Y\`pR�P�R�UtY*g�vwTXNZUIR�TINQVO�^FRwgiY\TXRy`pY*�ONZ[KstY\[�UIY�Y\UXm_R�TBTIR�n{]_R�PSU�Pw��zÖY{PXP�Nb^_fZR�vwTXNZUXR�TINeVyNZ[Fv�fZ]FMDR�TXR�n{]_R�P�UlV*TITXNZ�xV*fFUXNZ`aR�P.V*[ÐM U�V�TIs\R�Uvw|OfZNb[FMDR�T[O]_`�^FR�T�P*� �{VxvwY �O� �Ð��R�fZU �B> � ~ Y�é A 55�O��R�Y\T A 5_�{æ_TWV*[�C �  °�L�s\NZ[Ks�V*fbs\YxTINZUXm_`#PÖsxNZ�{R�d_TXNZYxTINZUS|�UXYTIRcno]_RcP�U�P2UImFV�U(mFV��{Rt^FR�R�[aNZ[aUXm_RtTXR�no]KR�P�UBn{]_R�]_RygiYxT(R�ÔKvwR�PXP�Nb�{RydFR�TXNZYOM_P(Y�g.UINZ`pR{��{Y\`aR�V*fbs\YxTINZUXm_`#Ps\TWV\MD]ÐV*fZfb|&Nb[FvwTIRcV\P�R�UXm_R�d_TXNZY\TXNZUS|)V\PtVaTXR�no]KR�P�U�V*sxR�P�� �{V\v�Y �D� �.�{R�fZU �B>  °��LyfbUIR�TX[FV*UXR�fZ|{�FVaUXNZ`aR�fZNb`aNZU`#V�|�^5R�P�R�U�VcgiUXR�T���m_Nev�m�TIRcno]_RcP�U�P�`aY��{R.UIY�Vym_NZsxm_R�T�d_TXNZYxTINZUS|{�.Ü°[�R�NZUXm_R�T.v�VxP�R{��NågÐV*[äV*sxNZ[_s�V�fZsxY\TINbUIm_`s\Nb�{R�PhUIY{Y�`�]Fv�my�BR�NZsxmDU.UIY�UIm_R�no]KR�]_R2UINb`aR } V�s\R\�qvwY\`adFYx[_R�[OU���NZU�MDR�sxR�[_R�TWV*UXR�PqNb[DUXYtæ ~ æ��â� û�YxUIf A 7B °�æ_Y\T�UIm_NeP(TIR�VxP�Yx[��hV�s\Nb[_saV�fZsxY\TINbUIm_`ÕP(` ]FPSU(^FR�v�V*TIR�gi]_fZfb|aMDRcP�NZsx[_R�M¢� d_TIRwgiR�T�V*^KfZ|pVcgiUIR�TtV�UIm_YxTIYx]_s\mV*[ÐV*fZ|KP�NeP(Y*g2UXm_R�P�dFR�vwNkjªvt�(YxTIÎOfZY{VxMaUIY�^5R�PXv�m_RcMD]_fZRcMh�

# ¡�©cR�¦ ` P ] £ _ Â Ä b4# 4c§«¤�R È 2 R b?Â Ä b�ÈFO £Q¡HRÜØgaR�[OUINbUINbR�P&V�^5Y��{R¢UIm_R¢PIv�m_R�MO]_fZR�T)d_TIY��ONQMDRÛNb[DgiY\TX`#V*UXNZY\[ V*^FY\]_U8TIR�n{]_R�PSU�NZ[OUIR�TXÏØTXR�fQV�UINZYx[FP�mKNZdFP

V*[ÐM5Ý�YxT�UIm_RúTIYxfZRúY*g�NZ[ÐMDNZ�ONQMD]ÐV*ftTXR�no]KR�P�UWPÕNb[¼Vxv�mKNZR��ONZ[_s³P�|KP�UIR�` s\Y{V�fQP } R{� sK�Z�ydFR�TSgiY\TX`#V*[Fv�RúV*[FMTIR�fZNQV�^_NZfbNZUS|�`aR�UXTINev�P��W�UIm_RàPIv�m_R�MD]_fbR�T�v�V�[�`aY\TXRaRwéªR�vwUXNZ�{R�fb|�giYOvw]ÐP Y\[¢NZ`ad_TXY��DNb[_s�Y��{R�T�V�fZf�PS|_PSUIR�`dFR�T�giYxTI`#V�[FvwR{�.�(m_R�TIR�PS]_fZUXNZ[_s�TIRcno]_RcP�U2Y\TWMDR�TINb[_s{P`#V�|äV\vwUX]FV*fbfZ|�^FR:�PS]_^FY\d_UXNZ`#V�ft<�V\P2`aR�VxP�]_TXR�M´^O|MDNeP�Î#PS]_^FP�|KP�UXR�`÷`aR�UITINev�Pw�

û�V*[_sxR�T�V*[ÐM�zV*UXUtdFR�T�giYxTI`aR�M#V�[�NZ[_NbUINQV�f.P�UX]FMD|&Y�gBMDNeP�Î)PIv�m_R�MD]KfZNZ[Ks ]FPSNZ[_sÕP�|KP�UIR�`aÏØfbR��{R�fFNZ[OgiY\TIÏ`#V�UINZYx[�Y\^_UWV*Nb[_R�M�giTIYx`�V��t�tÜ°ÿòjFfbR�P�|KP�UXR�`¼�èûtV�[_s � 7B °���(m_R�|�vwfeV\PIPSNåjFRcMrTIR�n{]_R�PSU�PVxPlUXNZ`aR�Ï°vwTXNZUXNQv�V�fØ�UINb`aR�ÏifZNb` NkUIRcMh��Y\TUXNZ`aR�ÏØ[_Yx[FvwTXNZUINev�V*f{^ÐV\P�RcM´Yx[ ��m_R�UIm_R�T�Y\T2[_Y\U2m_Y�P�U2d_TXYOvwR�PIPSR�P^_fZYOv�Î } Y\T��NbfZf_^KfZYOv�Î5�VcgiUXR�T�NQPXP�]_Nb[_s&UXm_R TXR�n{]_R�P�UWPw�p�(m_R�|ú`aYOMDNåjÐR�M�V&MDR��DNevwR�MDTINb�{R�TtR�ÔOR�vw]KUINZ[KsaUIm_Rp�ÖÞ�Þ�� PXv�mKR�MD]_fbNZ[_sV*fbs\YxTINZUXm_`áUIYasxNZ�{R�d_TXNZY\TXNZUS|aUXYaUINb`aR�ϾvwTINbUINQv�V*fªV*[FM&UXNZ`aR�ÏØfbNZ`�NåUXR�M�TIR�n{]_R�PSU�Pw��æ_Y\T�VäjFfbR�vwYx`ad_TXR�PIPSNZY\[�(YxTIÎOfZY�V\Mh�KV*d_d_fbNQv�V�UINbY\[�TI]_[OUINb`aR�PMDTXY\d_dFR�M � 7£� � 8 � ��mKR�[av�Y\`adFV�TIR�M�UIY�UIm_R�vwY\[O�{R�[OUINZYx[FV*fÐ�ÖÞ�Þ��PIv�m_R�MO]_fZR�T��&L�UrUXm_R#PXV*`aR�UINb`aR{��UIm_Rp`aR�V*[úTIRcno]_RcP�U�P�R�TX�DNevwR�UINZ`pR�NZ[FvwTXR�V\PSR�M"^O|´DTC � �UIm_Rp`aR�V*[P�R�R�Î�UINb`aR(Nb[FvwTIRcV\P�RcM´^O|�Y��{R�T � D >X� �FV*[FM�UIm_R�`aR�V�[�TIR�PSd5Yx[FP�R�UINZ`pR�NZ[FvwTXR�V\PSR�M�^D|�Y��{R�T2V�[aY\TWMDR�TBY*g`#V�s\[_NbUI]FMDR��y�(mKR�NZT��(YxTIÎ&dKfQV*Nb[_fZ|ÕMDR�`aYx[FP�UXT�V*UXR�MÓUXm_RrdFYxUIR�[OUINeV*f.^5R�[_RwjFUWPyY*gB`#V�ÎDNb[_s�P�|KP�UXR�`aÏifZR��{R�fNZ[OgiY\TI`ÕV*UINbY\[#V��xV*NbfQV�^_fZR�UIY�UXm_R�MDNQPSÎ#PIv�m_R�MO]_fZR�T��

� RcV*fZÏiUINb`aR�PS|_PSUIR�`0TXR�P�RcV*T�v�múmFV\PrTXR�vwR�[OUIfb|ÕgiYOv�]FP�R�MúY\[ÛMDNeP�Î8PIv�m_R�MD]KfZNZ[Ks#V*fbs\Y\TXNZUXm_`#PtUImFV�Ur]FPSRUITWV*[FPXV\vwUXNZYx[&MOR�V\MDfbNZ[_RcP�UIY�TXR�Y\TWMDR�T�Yx]_U�PSU�V*[ÐMDNZ[_spMDNeP�Î�TIR�n{]_R�PSU�Pw�2L�^_^FY\UIU�V�[FM&û�V*T�v�NQV*Ͼ�&Y\fbNZ[FVrmÐVc�{RP�UX]FMDNbR�MrPXv�m_RcMD]_fZNb[_s�V*fbs\YxTINZUXm_`#P�UImFV�UÖdKTINZYxTINbUINZÙ�R(MONQP�Î�TXR�no]KR�P�UWPq^FVxP�R�M�Y\[�UXm_R(d_TXNZYxTINZUS|tY�gªUIm_RBNQPIPS]_NZ[KsUITWV*[FPXV\vwUXNZYx[FP,� L�^_^FYHD �  �YxTtVpvwY\`�^_NZ[ÐV*UINbY\[aY�g2UITWV*[FPXV\vwUXNZYx[�d_TINbY\TINbUS|#V*[FM)P�R�R�Î#MDNQPSU�V�[FvwR��âLy^_^FY �T>  °��(m_R�|�PSm_Y�� UXmFV*UBUIm_R�giY\TX`aR�TdKTIY��DNeMDR�NZ`ad_TXY��{R�M�dFR�TSgiY\TI`ÕV*[FvwR�Y��{R�TBæ ~ æ��äV*[FM UXm_RtfeV*UIUXR�T2d_TIY��ONQMDRNZ`pd_TIY��{R�M�d5R�T�giY\TX`#V*[ÐvwRyY��{R�T2UXT�V\MONZUINbY\[FV�f�PSR�R�ÎOÏØTXR�MD]FvwNb[_s�V*fbs\Y\TXNZUXm_`#Pw��Ü°[ dFV�TIUXNQvw]_feV*T��_VrPXv�mKR�MD]_fbNZ[_sV*fbs\YxTINZUXm_` UImÐV*U�v�Y\[FPSNQMDR�TWPUIm_R�:�giR�VxP�Nb^_NZfbNZUS|o<�Y*g�MDR�VxMDfZNb[_R�P } N°�âR{�Z�\��mKR�UIm_R�T�YxT([_YxUBVrMDNeP�Î�v�V�[aPSR�TI�ONQvwRV TXR�no]KR�P�U�^FRwgiY\TXR�UIm_R�NePIP�]KNZ[_saUXT�V�[FPIVxvwUINbY\[�ç PtMDR�VxMDfZNb[_RrR�ÔOd_NbTIR�P��2NQPtPSm_Y���[�UIY#d_TIY��ONQMDR�UXm_R�m_NZsxm_R�PSUP�|KP�UXR�`0dFR�T�giYxTI`#V�[FvwR } V\P�`pR�V\PS]_TIR�M�^O|�UIm_R�[D]K` ^FR�T�Y*g�`aNePIPSR�M�MDR�VxMDfZNb[_R�P��W�aÜ°[úUIm_R jÐT�P�U�PSUI]FMD|��MDNeP�ÎúP�R�TI�ONQvwR�UXNZ`aR���V\P�m_R�feM"vwYx[FP�UWV*[OU�V*U,5 � `#P�d5R�TrTIRcno]_RcP�U��pÜ°["UXm_RaPSR�vwYx[FM"PSUI]FMO|{�ÖUXm_R�|�]FPSR�MV �{R�TX|)P�NZ`pd_fZR�MDNeP�Î#`aYOMDR�f.fQVxv�ÎONZ[Ks `aY�P�U�Y*gBUImKR�V\MD�xV*[ÐvwR�MÓgiR�V�UI]_TXR�PyY*g�Va`aYOMDR�TI[�MONQP�ÎàMDTINb�{R{��LzÖYxNQPIPSY\[pV*TXTINZ�xV�f_d_TIYOv�R�PIPÖ��V\P]FPSR�MrUIYtsxR�[_R�TWV*UXR�P�NZ[Ks\fZR�ÏØUXT�V\v�Î�MDNQPSÎrTXR�no]KR�P�UWPw�xV*[FM�P�UWV*TIUXNZ[_s�fZYOv�V�UINZYx[FP�(R�TIRt]_[KNågiY\TX`afZ|pMDNeP�UITXNZ^_]KUIR�Mh�

Page 32: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���

~ V*TXR�|{�FR�U�V*f¾�Z�_]FPSR�M�VaPSNZ`aNbfQV*TB`aR�UXm_YOMDY\fbY\sx|ÓUXYaR�ÔKV*`aNb[_R�V dKTINZYxTINbU�|OÏi^FV\PSR�M&�ÖÞ�Þ�� V�fZsxY\TINbUIm_`� ~ V�TIR�D �  °� L0`aYxTIR�v�Y\`ad_fbR�ÔÛm_Y{PSU#`aYOMDR�ft��V\Pa]FPSR�MÁUXYß`aYxTIRàvwfZY�P�R�fb|ßR�`�]_fQV�UIR#TIRcV*f�M_V*UWV*^FVxP�RV\v�UINZ�ONZUS|{���(m_R�NbT��ÖÞ�Þ�� V�fZs\YxTINbUIm_`áPSR�TI�ONQv�R�MaV*fbf�m_NZsxm&d_TXNZYxTINZUS|�TIR�n{]_R�PSU�P(^FRwgiYxTIR�PSR�TI�ONQv�NZ[_säV*[O|afZY��d_TXNZY\TXNZUS|aTXR�no]KR�P�UWPw���(m_R�|)TIR�vwYxs\[_NbÙ�R�MaUImÐV*UtUXm_Rr[O]_`�^5R�T�Y*g2d_TXNZYxTINZUS|afbR��{R�feP(NQP�NZ[O�{R�T�PSR�fZ|�TIR�feV*UXR�MÓUXYUImKR�`aR�v�mFV*[_Nev�V*f.MOR�fQV�|&TXR�MD]Fv�UINZYx[�dFY{PIPSNZ^_fbR ]ÐP�NZ[Ks&PS]Fv�m¥Va`�]_fZUXNZϾno]_R�]_R�PIv�m_R�MO]_fZR�T�ê�V#P�Nb`ad_fZR�US�(Y\Ïn{]_R�]_R�PIv�m_R�`aR�V*fbfZY���P(PSNZs\[KNåjªv�V�[DUBPXv�m_RcMD]_fZNb[_s�ªFR�ÔONZ^_NbfZNbU�|��*R�PSdFR�vwNQV�fZfb|�giY\TBm_R�V��ONZR�T�BY\TXÎDfbY{V\MKPw�2�(m_R�|vwYx[FvwfZ]ÐMDR�M&UImÐV*UrNbUtNQPtR�PXP�R�[OUINeV*fUXY#]FP�RpVÓd_TXNZYxTINZUS|OÏØ^ÐV\P�RcM�MDNQPSÎúPIv�m_R�MD]_fbR�T } NZ[8vwYx[\ùS]_[FvwUXNZYx["��NbUIm8Vd_TXNZY\TXNZUS|OÏØ^FVxP�R�M�^_]DéªR�TB`#V*[ÐV*s\R�`aR�[OUV�fZs\YxTINbUIm_`&�.��m_R�[_R��{R�TUXm_R�MDNeP�Î�PS]_^FP�|KP�UXR�`�NQP2V�dFR�TSgiY\TI`ÕV*[FvwR^FY\UXUIfZR�[_R�v�Îh�

~ m_R�[���R�U�V*f¾�Z��vwYx`adFV*TXR�MtUIm_R2dFR�TSgiY\TI`ÕV*[FvwR2Y�gªP�R��{R�T�V*fxTIR�V�fZÏiUINb`aR2PIv�m_R�MO]_fZNb[_s�V�fZs\YxTINbUIm_`#P��*Nb[Fvwfb]FMDÏNZ[KstUIm_R�^FR�P�UlV*fZsxY\TXNZUImK`#PqgiTIYx`¼�âLy^_^FY �T>  FV*[FM¬� ~ V�TIR�D �  FV*fbY\[_s���NbUIm�US�(Yt[KR��ßTXR�V*fbÏØUXNZ`aRBV*fbs\YxTINZUXm_`#P^FVxP�R�M#Y\[¥�_�O��æ � ~ m_R�[ �D�  ¾���(m_R �K�O��æÖÏi^FV\PSR�M�V*fbs\Y\TXNZUXm_`#P(]FPSRr^FY\UXmúP�R�R�ÎÕMDNQPSU�V*[ÐvwR�P�V*[FM&TXR�no]KR�P�UMDR�VxMDfZNb[_R�PyNb["UXm_R�s\R�[_R�T�V*UXNZYx["Y�g�TIR�n{]_R�PSUtY\TWMDR�TINb[_s{P��a�(m_RpV*fbs\YxTINZUXm_`#P�v�V�["^FR�^_NQVxP�R�M�UIY���V�T�M"R�NZÏUImKR�T2Y*g.UImKR�vwTINbUIR�TXNQVy^O|�v�mFV*[_sxNZ[_sävwR�TXU�V*Nb[aPXv�mKR�MD]_fbNZ[_s�dFV�T�V*`pR�UIR�TWPw�.�(m_R�v�Y\`ad_TXR�m_R�[ÐP�NZ�{R�M_V*UWV*^FVxP�R`aYOMDR�f�]FP�R�M&Nb[&UXm_RrR�ÔOdFR�TINb`aR�[OU�P2��V\P��\V�fZNeM_V*UXR�M&V�s{V*Nb[FP�U�V�[úV\vwUX]FV*f.TIR�V�fZÏiUINb`aR�M_V*UWV*^FVxP�R�UIRcP�UI^FR�Mª�^_]_U�UXm_RaMONQP�Î�`pYOMDR�f��V\P��{R�TI|�PSNZ`adKfZNQPSUINev\��Ü°["dÐV*TIUXNQvw]KfQV*T���UIm_R�fQVxv�Î)Y*g�V*[úY\[KÏØ^FY{V�T�M¢M_V*UWV&v�Vxv�m_RNZ[8UIm_R)MDNeP�Îú`aYOMDR�fB]_[FMDYx]_^_UIRcMDfZ|ÛV�éªR�vwUIRcM"UIm_R#dFR�TSgiY\TI`ÕV*[FvwRpTIR�PS]_fZUWP�giY\T�UXm_R�NbTrR�ÔOdFR�TINb`aR�[OU�Py]FPSÏNZ[Ks��(Y\TXÎDfbY{VxM_P´��NbUIm¥mKNZs\m¢Vxv�vwR�PXPrfZYOv�V�fZNZUS| } ]_dÛUXYúV > �6D�P�Rcno]_R�[DUXNQV*f�V\v�v�R�PIP�d_TIYx^FV*^_NbfZNbU�|F���8�&Y{PSUY*g�UImKR�NZT�R�ÔOdFR�TINb`aR�[OU�P��*m_Y��BR��{R�T��KV\PXP�]_`aRcMaVr]_[_NkgiY\TI` MDNQPSUITINb^_]_UXNZY\[#Y�gTXR�no]KR�P�U�P�U�V�TIUXNZ[_s�fZYOv�V�UINbY\[FP��æ_Y\TBUIm_R�NbT�PSNZ`�]_fQV�UINZYx[�R�[O�DNbTIY\[K`aR�[OU���UIm_R�US�(Y��_�O��æÖÏi^FV\PSR�M#V*fbs\Y\TXNZUXm_`#Pd_TIY��ONQMDRcM UIm_R�^5RcP�U�PS|_PSUIR�`dFR�T�giYxTI`#V�[FvwR{�

�tNZ`ÚV*[FM&�{TXNZ�xV\PSU�V��xVrR�Ô_V�`aNZ[KR�M´TXR�V*fbÏØUXNZ`aR�MONQP�ÎÕPIv�m_R�MD]_fbNZ[_s�V�fZs\YxTINbUIm_`#P2UImFV�U�MDNåéªR�TXR�[OUINQV�UIRt^FR�ÏUS�(R�R�[¥TIR�VxM_P�V*[ÐMò��TINbUIR�Pr��mKR�[¢V\PIPSNZsx[_NZ[_súTIRcno]_RcP�UrdKTINZYxTINbUINZRcP� �tNb` �D�  °�8�(m_R#^FR�P�U�dFR�TSgiY\TI`ÕV*[FvwRTIRcP�]_fbUIR�MagiTIY\`�V*[úV�fZs\YxTINbUIm_`áUImÐV*U�V\PXP�NZsx[FPyTXR�V\M&TXR�no]KR�P�U�d_TINbY\TXNZUINbR�P�^FV\PSR�M&Y\[�UXm_R�d_TINbY\TXNZUS|aY*gBUXm_RNQPXP�]_Nb[_stUXT�V*[ÐPIV\v�UINZYx[�V*[FM���TINbUIRBTIR�n{]_R�PSUÖd_TXNZYxTINZUXNZR�P�^FVxP�R�MrYx[�UIm_R�d_TXNZYxTINZUS|�Y*gªUXm_R(UXT�V*[ÐPIV\v�UINZYx[FP��V�NZUIÏNZ[Ks´giYxTtUIm_R�TIR�fbR�V\PSRrY�g2UIm_RävwY\TXTIR�PSdFY\[FMDNb[_s#��TINbUIR�fZYOv�Î_P���ܾgl[_YaUITWV*[FPXV\vwUXNZYx[�NQP���V*NbUINb[_s´giYxT�V ��TXNZUIRUIY�v�Y\`ad_fbR�UIR��oUXm_R���TINbUIRtNeP�P�R�U�UXY�UIm_R�fZY��BR�P�U�d_TXNZYxTINZUS|�dFY{PXP�Nb^_fZR{�B�(m_R�NbT�PSNZ`�]_fQV�UIY\T�MDNQMa[_YxU�NZ[Fv�fZ]FMDRV�MDNQPSÎa`aYOMDR�f¾ê{UIm_R�|ÕV\PIPS]_`aR�MpVäjFÔOR�M#MDNeP�Î#PSR�TI�ONQvwR�UINZ`pRyY�g�5 � `#P��

Ü°[rUImKR�V*^ÐP�R�[Fv�R(Y*gªR�ÔOd_fbNQvwNbU�P�|KP�UXR�`aÏifZR��{R�f�NZ[DgiYxTI`#V�UINbY\[��xP�Yx`aRBPIv�m_R�MD]_fbR�T�Ph`ÕV*Î{RBvwR�TXU�V*Nb[�V\PIPS]_`ad_ÏUINbY\[FP�V�^5Yx]_U�TIRcno]_RcP�Utd_TXNZYxTINZUXNZR�P���æÐYxT�R�Ô_V�`ad_fbR{��V#PIv�m_R�MD]KfZR�T�v�V*[ús\NZ�{R�d_TXNZY\TXNZUS|&UXY#TIR�VxM�TXR�no]KR�P�UWP} Y��{R�T���TXNZUXRtTIR�n{]_R�PSU�P��(Nb[&V�[�V�UIUIR�`ad_U(UXY TXR�MD]Fv�RrV�d_d_fbNQv�V�UINZYx[#TI]_[OUINb`aR�Pw���(m_NQP�m_R�]KTINQPSUINevyNQP�MDTXNZ�{R�[^O|ÓUXm_Rtg¾V\vwU�UImÐV*U�V�d_d_fZNev�V*UXNZYx[&d_TXYOvwR�PIPSR�P�Y*giUIR�[���V*NbU;giYxTyTXR�V\M#TIR�n{]_R�PSU�P��5��m_NbfZR���TINbUIR�TIRcno]_RcP�U�P�V*TXR]FPS]FV*fbfZ|#^_]DéªR�TXR�MÓNb[&`#V�NZ[a`aR�`aY\TX| ]FPSNZ[_s���TINbUIR�Ïi^FVxv�Î#MONQP�Î)v�Vxv�mKR�Pw����[DgiY\TXUI]_[FV�UIR�fb|{�FP�]Ðv�m)m_R�]_TXNQP�ÏUINev�PrV�TIR#Y\[KfZ|¥RwéªR�v�UINZ�{R�NZ[¢vwR�TIU�V�NZ[ÛPSNZUX]FV*UXNZY\[ÐP�V*[FMÛ`#V�|úV\vwUX]FV*fbfZ|ÛMDR�s\T�VxMDR#dFR�T�giYxTI`#V�[FvwR#MD]KTINZ[Ks^_]_TWP�UWP�Y�gBm_R�V��D|)VxvwUINb�DNbU�|��tÜ°UtNQP�R�V\PS|&UIYÕMDR��ONQP�R�v�V\P�RcPy��m_R�TXR�Y\d_UXNZ`#V�f�d5R�T�giY\TX`#V*[ÐvwRrTXR�no]KNZTIRcP;UXm_RPIv�m_R�MO]_fZR�T�UIY&sxNZ�{R�d_TXNZYxTINZUS|)UIY&��TXNZUXR�TIR�n{]_R�PSU�P } Y��{R�TtTXR�V\MúTIR�n{]_R�PSU�P��W�aæ_Y\T�R�ÔKV*`pd_fZR{�ªP�dFR�v�]_fQV�UINZ�{Rd_TXRwgiR�U�v�maTXR�no]KR�P�UWP(NQPIPS]_R�Ma^O| jFfZR�PS|_PSUIR�`#P2Y\T�V*d_dKfZNQv�V*UINbY\[FP�PSm_Y\]KfQMÓ[KY\U�^5R�s\Nb�{R�[ad_TXR�vwR�MDR�[FvwRtY��{R�TP�|O[Fv�m_TIYx[_Y\]ÐP;��TXNZUIR�TXR�no]KR�P�UWP } R{� sK�Z�ojÐfZR�P�|KP�UXR�`÷`aR�UWV\M_V�U�Vr]_dªM_V�UIR�P�����L�PyV�`aY\TXR�vwYx`ad_fZR�Ô�R�Ô_V�`aÏd_fbR{�5NkgBVaMDNeP�Î#^_fbYOv�Îàv�V\v�m_RrNb[&`#V�NZ[#`aR�`pY\TI|pv�V�[_[_Y\U�m_Y\feM�V*[O|&`aYxTIR�MDNZTXUS|Ó^KfZYOv�Î_P��5NbUyNePy�DNbU�V�fÖUXYn{]_NQv�ÎDfb|tv�fZR�V�[�P�Yx`aRgiT�VxvwUINbY\[�Y*gÐUIm_R�v�V\v�m_R } P�R�R�P�R�v�UINZYx[,5O�65D�U5o�W��û�NZ�ONZ[_s���TINbUIRBTIR�n{]_R�PSU�P�fZY��¥d_TXNZY\TXNZUS|P�fbY���P;UXm_R�d_TIYOvwRcPIP(Y*g�vwfZR�V�[_NZ[Ks�UIm_R�MDNeP�Î#v�Vxv�mKR{�DNb[FMDNZTXR�vwUXfZ|�TIRcMD]FvwNb[_s�V�d_d_fZNev�V*UXNZYx[ÓdFR�TSgiY\TX`#V*[Fv�R{�

Page 33: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5 >

¯��°¯ $&�� ���¤¥%��´���÷/ +p+ ® ,{+ �KMQ® ±�� + ����® ������(m_NQP.v�mFV*d_UXR�T.MDR�PXvwTINb^FR�PhUIm_RBPSU�V*UXR�ÏiY*giÏiUIm_R�ϾV*TXUNZ[�MDNeP�Î�PXv�mKR�MD]_fbNZ[_sK� ~ fZR�V�TIfb|{��P�Nbs\[_Nkjªv�V*[OU.TIY{Y\`¼giYxT

NZ`pd_TIY��{R�`�R�[{UhR�ÔDNeP�U�P��.Ü [OUIR�T�g¾V\v�R�PÖV�[FMrd_TXY\UIYOv�Y\fQP2PSm_Y\]_feMr^FR�V*]Ks\`aR�[OUIRcM�UIY�V*fbfZY��Û]FP�R�gi]_f_PXv�mKR�MD]_fbNZ[_sNZ[OgiY\TI`ÕV*UINbY\[)UIY#TIR�Vxv�múV#vwR�[DUXT�V*fbNZÙ�RcMÓPXv�mKR�MD]_fbR�TyYxT�dFV\PXP�^FR�US�BR�R�[�MONQP�UXTINb^_]_UIRcM�PIv�m_R�MD]_fbR�T�P�� ~ Y\`aÏdFY\[_R�[DUWP�V*fZYx[_s�UIm_R�ÜIÝ\Þ dFV*UXm&PSm_Y\]KfQMÓ^FR�`aYOMDNkjFR�M�UIY�R�ÔOUIT�VxvwU�V�[FMÓdÐV\PIP�PS]Fv�mÓNb[DgiY\TX`#V*UXNZYx[aUIY�UXm_RPIv�m_R�MO]_fZR�T } P���� ~ R�[OUIT�V�fZNbÙ�R�M&PXv�mKR�MD]_fbNZ[_s#V�fZsxY\TINbUIm_`ÕP�PSm_Y\]KfQM�^5Rp]_d_s\TWV\MDRcM�UXY&]_UXNZfZNbÙ�Rr`pY\TIR�Y�g�UXm_RV��xV*NZfeV*^_fbRrNb[DgiY\TX`#V*UXNZY\[±�FV*[FMúMDNQPSUITXNZ^_]_UXR�M#PIv�m_R�MD]KfZNZ[KsaV�fZs\YxTINbUIm_`#P�P�mKY\]_feM&^5R�MOR��DNeP�R�MaUXmFV*U�R�[FV�^_fZRvwY{Yxd5R�T�V*UXNZ�{R�PIv�m_R�MO]_fZNb[_s_�

Ltv�vw]KT�V*UXR�fZ|�NQMDR�[DUXNågi|ONZ[_stR�éhRcvwUINb�{R�PIv�m_R�MD]_fbNZ[_s�V�fZs\YxTINbUIm_`#P2V�[FM#PIv�m_R�MD]_fbR�TNb`ad_fZR�` R�[OU�V�UINbY\[FP�TIR�Ïn{]_NZTXR�PtV ^FR�UXUIR�TtdFR�TSgiY\TX`#V*[Fv�RrR��xV*fb]FV*UXNZYx[�`aR�UImKYOMDY\fbY\s\|)UImFV�["mÐV\Pt^FR�R�[�]FPSR�M�Nb[&d_TXR��ONZY\]ÐPy�(YxTIΪ��(m_RÛPSUI]FMONZR�P�MDNePIvw]ÐPIP�RcM¼V*^FY��{RÛV*fbf�PS]DéªR�T&giTIYx` Yx[_R¥Y\T�`pY\TIR�g¾V*NbfZNb[_s{P��0�&Y{PSU�]FP�RÛMONQP�Χ`aYOMDÏR�feP´UXmFV*U�fQVxv�ÎÛNZ`pd5YxTIUWV*[OU�MDNQPSÎßMOTINZ�{R)v�mFV*TWV\vwUXR�TINeP�UXNQv�P } R{� sK�Z�2TIR�n{]_R�PSU d_TXYOvwR�PXP�NZ[Ks"Y��{R�TXm_R�V\MKPw�(Yx[_Ï^FY{V�T�M§M_V*UWV¥v�V\v�m_R�P���V*[FM�vwYx`ad_fbR�Ô¥MKV*U�V¥feVc|{Yx]_U�P���� �(m_R&R�ÔOdFR�TINb`aR�[OU�P�U�|Od_Nev�V*fbfZ|¥]FPSR�PS|D[OUIm_R�UINQv�(YxTIÎOfZY�V\M_P#��NZUIm P�NZ`pd_fZR�d_TXY\^FV�^_NZfbNZUS|§MDNeP�UITXNZ^_]KUINZYx[FP giY\T)TIR�n{]_R�PSU�P�UWV*TXUINZ[KsßfZYOv�V*UINbY\[FP } R{�âs_�b�t]_[_NZÏgiY\TX`���]_[_NZ`pYOM_V*f¾�rY\T�^_Nb`aYOM_V�fØ������m_NQv�móV*TXRß]_[KTIR�d_TXR�P�R�[DUWV*UINb�{R"Y�g#`aY�P�U&TXR�V*fbÏØ�BY\TXfQM¼�(YxTIÎOfZY{VxM_P� � ]_R�` � 7{�2ë�V*UXR �D� �(×yR�[_ftD � �B��v��y] DBCD�(�ovwT�VTDB7_�2�h|O[Fv A 5B ¾�ß�(mKY{P�RúPSUI]FMONZR�PrUXmFV*U#MONQM¥NZ[O�{Y\fb�{R#V\vwÏUI]ÐV*f.NZ`ad_fbR�`aR�[DUWV*UXNZY\[p]FP�R�M&�{R�TI|#PSNZ`ad_fbNQPSUINQv�^FR�[Fv�m_`#V�TIÎKPw����NZUXmÓgiR��¼R�Ô_vwR�d_UINbY\[FP��5d_TXR��ONZY\]ÐP;�BY\TIÎNZsx[_Y\TXR�M&m_Y�P�UygiR�RcMD^FV\v�Î#RwéªR�vwUWP } R{� sK�Z�F^D|#]FPSNZ[_s#VpzÖY\NePIP�Yx["dKTIYOvwR�PXP;giY\T�TIR�n{]_R�PSUtV�TITINb�xV*fQP���Y\T�Y*�{R�TIÏP�Nb`ad_fbNåjFR�M�UImKR�` } R{� sK�Z�O^D|a`ÕV*NZ[OU�V�NZ[_Nb[_s�V�v�Y\[FPSU�V*[OU�[D]_`�^FR�T(Y�gYx]_U�PSU�V�[FMDNZ[KsaTIR�n{]_R�PSU�P����

Page 34: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��� ��� ö ñ>/ ³

õ �y�2' + � + � + �¦¥

�(m_R�R�ÔDdFR�TXNZ`aR�[DUWPhNZ[�UIm_NePMDNQPXP�R�TXU�V�UINZYx[ Nb[D�{YxfZ�{R2giY\]_T2R�fbR�`aR�[OU�P��hVtUITWV\vwR�Ï°MDTXNZ�{R�[�PSNZ`�]_fQV�UIYxTvwYx`aÏd_TXNQP�RcM Y*g�MDR�U�V*NbfZR�M�`aYOMDR�fQP�Y�g.^FY\UIm#UXm_Rtm_Y�P�U�V*[ÐMÕUXm_R�MDNeP�Î�PS]_^FP�|KP�UXR�`�êOV�P�R�U(Y*g.UXT�VxvwR�P } dKTINZ`ÕV*TINbfZ|U�V�Î{R�[�giTXY\`óTIRcV*fZÏi�(YxTIfeMrP�|KP�UXR�`#P��F]FP�R�M�VxPÖNZ[Kd_]_U.UIYtUXm_R�PSNZ`�]_fQV�UIY\T�ê�UIm_R�MDNQPSÎ�PIv�m_R�MD]_fbNZ[_s�V*fbs\YxTINZUXm_`#PV*[ÐMaPIv�m_R�MD]KfZR�T2NZ`pd_fZR�`�R�[{UWV*UINbY\[FP.^5R�NZ[_säP�UI]ÐMDNZR�MªêDV�[FMaUIm_R�dFR�T�giYxTI`#V�[FvwR�`aR�UXTINQv�Pq]FPSR�M UXYrR��xV*fb]FV*UXRPIv�m_R�MO]_fZR�T�MDR�PSNZs\[ÐPw�2�(m_NePyv�mFV*dKUIR�T�MDRcPIvwTXNZ^FR�P�RcV\v�mÓY�g2UImKR�giYx]_T�R�fbR�`aR�[OU�P��

³��?� ö�')� $&�® !������� + � õ + �)���LtP�dFV*TXUtY*g�V feV*TIsxR�TtTXR�P�R�V�T�v�m#RwéªY\TIU�NZ[OUIY#ÜIÝ\ÞãPS]_^FPS|_PSUIR�`�MDR�P�Nbs\[)NQPIPS]_R�P���V*[�R�ÔOUIR�[FP�Nb�{RtUITWV\vwR�Ï

MDTXNZ�{R�[úPSNZ`�]_fQV�UIY\T���VxP�MDR��{R�fbY\dFR�MÓgiY\T�PSUI]FMD|ONZ[Ks&MONQP�ÎàP�]_^ÐP�|KP�UIR�`#Pw��Ü°U�vwYx[DUWV*NZ[ÐPy` ]KfZUINbd_fZR�`aYOMOR�fQPY*g�m_Y�P�U�P�|KP�UXR�`#P��D^_]FPSR�Pw�Kv�V\v�m_R�P��_vwYx[DUXTIYxfZfZR�T�Pw�KV*[FM#MDNeP�ÎpMDTINb�{R�Pw���(m_R�P�Nb`ad_fZRcP�U2m_Y{PSU�`aYOMDR�fª`aR�TXR�fZ|NZ[OUIR�TId_TXR�U�P�UITWV\vwR�P�Y*g;MDNQPSÎ#TIR�n{]_R�PSUtVxvwUINb�DNbU�|��t�(m_R�`aY{PSUtvwYx`ad_fbR�Ôam_Y�P�U�`aYOMDR�f.PSNZ`�]_fQV�UIR�P(UXm_R�R�ÔOR�Ïvw]_UXNZYx[&Y*g�V*d_d_fbNQv�V�UINbY\[)V*[FM"Þ�Ýx�ad_TXYOvwR�PIPSR�P�Y\[�Y\[KRrY\T�`aYxTIRtd_TXYOvwR�PXP�Y\TWPw���(m_RäMDNQPSÎÓ`pYOMDR�fQP2T�V�[_s\RgiTIYx` PSNZ`ad_fbR#P�UWV*UXNQP�UXNQv�V�ftMOR�fQV�|Û`aR�v�mFV*[KNQP�`ÕP�UIY³MDR�U�V�NZfbR�Mh�(m_Nbs\m_fb|DÏi�xV*fbNQM_V�UIR�MÛ`aYOMDR�feP´Y�gr`pYOMDR�TI[� ~ �OÜBMDNQPSÎ#MDTXNZ�{R�P��

§ ?�¸(?�¸ ¨óA�½DC�¹ Ayºt<�W�½�(m_R�P�Nb` ]KfQV*UXY\T�PS]_d_dFY\TXU�P�P�R��{R�T�V*f�mKY{P�U�`aYOMOR�fQP(UXmFV*U�v�Y\[FPS]_`aR�MONåéªR�TIR�[DU�US|Od5RcPyY*gBUITWV\vwRcPw�tæ_YxT

R�ÔOdFR�TINb`aR�[OU�P�MDTINb�{R�[¥^O|F¦ ] §?à b R J ` R�§J¤�¤ b�O ¡HR�§x�TIR�n{]_R�PSU�V*TITXNZ�xV*feP�V*TXR&`aYOMDR�fZR�M¥VxP´Nb[¢V*[ÛY\dFR�[P�|KP�UXR�`�� � R�n{]_R�PSU�P�V*TIR)NQPXP�]_R�M¥UXY�UIm_R)MDNeP�ÎÛPS]_^FP�|KP�UXR�` `aYOMOR�f(]FPSNZ[_súUITWV\vwRcM³Nb[DUXR�T�V�TITXNZ�xV*fBUINZ`pR�P} ��NbUIm_Yx]_U�TIR�s�V*TWM�giY\T�TIRcno]_RcP�U�vwYx`ad_fbR�UINbY\[&UXNZ`aRcP����ä�(m_R YxdFR�[¥PS|_PSUIR�`ÑV�d_d_TXY{V\v�mú��V\P�v�mKY{P�R�[�giYxTUS�(Y#TIRcV\P�Yx[FPw�#æ.NZT�PSU���NZU�TXR�U�V�NZ[FPtUImKR ^_]KT�P�UXNZ[_RcPIP�Nb[_m_R�TXR�[OUtNZ[úTIR�V�f�(YxTIÎOfZY�V\M_P } V\P�Y\d_dFY�P�R�M¥UIY#UXm_RjFÔOR�M�n{]_R�]_R�fbR�[_s\UXmFPY*g±UIm_R�vwfbY{PSR�M�P�|KP�UXR�` V�d_d_TIY�V\v�mh���(��R�vwY\[ÐMh�OPIv�V�fZNZ[Ks�Y�g�UXm_R�UITWV\vwR�MrNb[DUXR�T�V�TITXNZ�xV*fUINb`aR�P2vwTXR�V*UXR�P�V PS`aY{Y\UXm)vwY\[OUINb[D]_]K` Y�g2�(YxTIÎOfZY{VxM_Pw�

æ_Y\T�R�ÔDdFR�TXNZ`aR�[DUWP�MOTINZ�{R�[¥^D| Â�` PSP,§w4c§«¤ER È ¤ b�O ¡HR�§\�(V�`aYxTIR#MDR�U�V*NbfZR�M¥m_Y�P�U�`aYOMDR�f�dKTIY��DNeMDR�PTIRcV*fZNeP�UXNQvygiR�R�MD^ÐV\v�ÎÓ^ÐV\P�RcM&Y\[�TIRcno]_RcP�U�vwY\`adKfZR�UXNZY\[ÐPw���(m_R�Á b Ä�¡HR�§G§�G�©ôÄXÆ È Ä�¦cR�P�TIR�d_TIYOMD]ÐvwR�PyUXm_RR�ÔOR�vw]_UXNZYx[ßY*g�d_TXYOvwR�PXP�R�P Nb[ßUXm_R�m_Y{PSU#P�|KP�UXR�` V�[FMßUImKR�NZT�NZ[OUIR�TWV\vwUXNZYx[ß��NZUXmßUXm_RúMDNQPS΢P�]_^FPS|_PSUIR�`� û�V�[_s � 7B °�tÜ°U�TIR�v�TIR�V�UIR�P(R�Vxv�m)d_TIYOv�R�PIPy^O|)vwY\[ÐP�]_fbUINZ[Ks#V´UXNZ`aRcP�U�V�`adFR�M UXT�V\v�RrY*gBNb`adFY\TIUWV*[OU�R��{R�[OU�PR�[Fv�Y\]_[OUIR�TXR�M�MD]_TXNZ[_sÛUXm_R�fZNkgiR�UINb`aRaY*gäUImFV�U&d_TXYOvwR�PXP } R{� sK�Z�(giY\TXÎh��R�ÔONZU���P�fbR�R�d���V*[ÐM MDNeP�Î�TXR�no]KR�P�Us\R�[_R�T�V�UINbY\[h�W�Ü°U.V*feP�Y�s\R�[_R�T�V*UXR�P.V*[FMrmFV�[FMDfbR�P�vwfZYOv�Î�V�[FM�ÜIÝ\Þ¥Nb[DUXR�TITX]_d_UWPw�.ë(R�v�V�]FP�R2UImKR(d_TXYOvwR�PIPSÏ ªÐY*�`aYOMDR�f_PSNZ`�]_fQV�UIR�PFm_Y��ßd_TXYOvwR�PIPSR�PÖNb[DUXR�T�VxvwUÖ��NbUIm�UIm_R�NbTMONQP�Î�TIR�n{]_R�PSU�P��*NbUR�[FV�^_fZR�P�UImKR�dFV*TXUINZUXNZYx[_NZ[_s�Y*g

5 �

Page 35: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5B5

×�z ~ 5B5�8 A u NQP�Î u TINb�{Ræ_Y\TI`ÕV*UIUXR�M ~ V�dFV\vwNbUS| � � >x� û�ë

� z2� � 8 >T>�&RcV*[��{R�R�ÎÕ�(NZ`aR ª �?> `#Pu V�U�VÓ�{]KT�g¾V\v�R�P � 7

~ |OfZNb[FMDR�TWP 5 >\�O��{R�v�UIY\TWP 5 >\� 8HDTC�8YFYx[_R�P D

�{R�v�UIY\TWP�Ýc�qTWV\v�Î � C*Ï � CÜ [OUIR�T�g¾V\v�R � ~ �OÜ°ÏÌ5~ V\v�m_R 5 � Cp��ë

��O 3cPwR¬«�%('*)�ë�V\PSNQv ~ mFV�T�VxvwUIR�TXNQPSUINQv�P(Y*g2UXm_R�×tz ~ 5T5�8 A u NQPSÎ u TINb�{RMDNeP�Î#TIR�n{]_R�PSU�P(Nb[DUXY `�]_fZUXNZd_fbRtv�fQV\PXP�R�P�� u NQPSÎ&PXv�mKR�MD]_fbR�T } P��Bv�V�[&]FPSRrUImKNQP�vwfQVxPIP�Nkjªv�V�UINZYx[&Nb[DgiY\TX`#V*UXNZY\[UIY�UI]K[_R�PIv�m_R�MD]_fbR�PlgiYxT�^FR�UIUXR�T�Y��{R�T�V�fZf�PS|_PSUIR�`Úd5R�T�giY\TX`#V*[ÐvwR{�

§ ?�¸(? · »¼G�½o¾¼»¼7_GÌ¿B< ¹ A=ºt<�W�½�(m_RpP�NZ`�]_feV*UIYxTtv�Y\[OU�V*Nb[FPtV�fZfY�g�UImKR�`aYOMDR�TX[úMDNQPSÎ�MDTXNZ�{R�giRcV*UI]KTIR�PtMOR�PIvwTXNZ^FR�M&Nb[úP�R�vwUXNZYx[¢5D� � � � �

NZ[ÐvwfZ]FMONZ[_saÙ�Y\[_R�M�TIRcvwY\TWMDNZ[_sK�.P�dFV�TIR�TIR�sxNZY\[ÐPw�.MDRwgiR�v�U�P�fbNZd_d_Nb[_s#V�[FM"TIRcV*fZfbYOv�V*UXNZYx[��.MDNQPSÎ&^_]DéªR�TWP�V*[FMv�Vxv�m_RcPw�\�xV*TXNZYx]FPd_TIRwgiR�U�v�m�V*fZsxY\TXNZUImK`#Pw��g¾V\PSU(��TINbUIR�P��\^_]FP2MDR�fQV�|_P��{vwYx[DUXTIY\fÐV*[FM�vwY\`p` ]_[KNQv�V�UINZYx[�Y*�{R�TIÏm_R�VxM_Pw�±V*[FM�vwYx`a`#V�[FMan{]_R�]_R�Nb[_s_��æ_Y\T�UIm_RäP�UI]ÐMDNZR�P�TIR�d5YxTIUXR�M&NZ[)UIm_NePyMDNePIPSR�TIUWV*UINbY\[��FUImKR�P�NZ`�]_feV*UIYxT��VxP�vwY\[OjFs\]_TXR�M UXY�`aYOMDR�fFUImKR�×tz ~ 5B5�8 > fZNZ[KRyY�g�MDNQPSÎaMDTXNZ�{R�P=�â×tz � 5� ¾�2�ÖV�^_fZR�8_� � fZNeP�U�PBP�Yx`aRy^ÐV\P�NevP�dFR�v�Nåjªv�V�UINbY\[FP�giYxTyUXm_R�×tz ~ 5T5�8 A � ×tz � 5xV� ¾�

�qY¢Vxv�vw]_TWV*UIR�fZ|Û`aYOMDR�f�UXm_NQP�fZNZ[KR&Y*gäMDTXNZ�{R�P���V*[�R�ÔDUXR�[FP�Nb�{R)P�R�UaY�g�dFV*TWV*`aR�UXR�T�P���VxPaY\^_UWV*NZ[KR�MgiTIYx` d_]_^_fbNQPSm_R�M�MDYOvw]_`aR�[DUWV*UINbY\[�V�[FM´^O|�`aYx[_NZUXY\TINb[_sr� ~ �oÜV\vwUXNZ�ONZUS|{�.�(m_R�R�ÔOd5R�TINZ`pR�[DUWV*f{d_feV*USgiY\TI`vwYx[FP�NeP�UIRcMòY*gäV�[�� ~ � 7 �x�B> `�]_fZUXNZd_TXYOvwR�PIPSY\T�PS|_PSUIR�` R�n{]_NZdKd5RcM³��NbUImü� ~ � � 7 ~ AE>B> � ~ �OÜ�ÜIÝ\Þd_TXYOvwR�PIPSY\TWP�V*[FM�×tz ~ 5T5�8 A MONQP�Î�MOTINZ�{RcPw��ÔOUITWV*[_R�Yx]FP(PS|_PSUIR�`�VxvwUINb�DNbUS|���V\P2`aNZ[_Nb` NbÙ�R�MrMD]_TXNZ[_s�UXm_R`aYx[_NZUXY\TINb[_s&dKTIYOvwR�PXP´UXY�TIR�MO]FvwR#m_Y{PSU�MDR�feVc|KPw�¥ýBV�TINZYx]FPr`aR�v�mFV�[_NQv�V�fdFY{PSNZUINbY\[_Nb[_s8MDR�fQV�|KPw�2vwYx[DUXTIYxfV*[ÐM�vwY\`a`�]_[_NevwV�UINbY\[aY��{R�TXm_R�V\M#�xV*fZ]KR�Pw�FdFV*UXm�UITWV*[FP°giR�TyTWV*UXR�Pw��V�[FM�v�Vxv�m_R�`#V�[FV*sxR�`aR�[OU�PSUITWV*UIR�s\NZRcP�(R�TIR�R�ÔOUIT�VxvwUIRcMh���Ô_VxvwU���ë��yÏiUIYxÏ°z2ë��>`ÕV*d_d_Nb[_s{P(�BR�TIRäMDR�UXR�TI`aNb[_R�MrgiY\T�P�R��{R�T�V*f.MONQP�ÎKPw�_dKTIY��DNeMDNZ[KsNZ[OgiY\TI`ÕV*UINbY\[)Y\[úÙ�Y\[_Nb[_s_�.PSdFV*TXNZ[_sK�ÖV�[FM¥MDR�giR�vwU�P��r�(mKR�V*d_dFR�[FMONZÔ�d_TXY*�ONQMOR�PtV#vwY\`pd_fZR�UXR�fZNQPSUyY�g�UXm_RMDNeP�ÎadFV�T�V�`aR�UIR�T�P(V�[FMÓR�ÔDUXT�V\v�UIR�M �xV�fZ]_R�P��

�(m_R#MDNeP�Î�`aYOMOR�f2��V\P��xV*fZNeM_V*UXR�M"^O|�R�ÔOR�T�vwNeP�Nb[_s#V*[¢VxvwUI]FV�f�×tz ~ 5B5�8 A V�[FM¥v�V�d_UI]KTINZ[Ks&UITWV\vwRcPY*g�V*fZf� ~ �OÜ(VxvwUINb�DNbU�|���(m_RäP�NZ`�]_feV*UIYxT(TXR�d_fQV�|{R�M�R�Vxv�m#UITWV\vwRcMÓTIRcno]_RcP�U�PSUITXR�V*`��O]FP�Nb[_s�UIm_R�Y\^ÐP�R�TX�{R�MNZ[OUIR�T�V*TXTINb�\V�f.MDR�feVc|KPw���(m_NQP�d_TIYOvwRcPIPy��V\PtTIR�dFR�V�UIR�MagiY\T�PSR��{R�TWV*f�P�|O[DUXm_R�UINevt�(Y\TXÎDfbY{VxM_Py��NZUXm��xV*TI|ONZ[KsTIRcV\M5Ý���TINZUXRrTWV*UINbY{P��FV*TITXNZ�xV*f.T�V�UIR�P��5TXR�n{]_R�P�U�PSNZÙ�RcPw�_V�[FM�MDR�sxTIR�RcP(Y*gBPSR�no]KR�[DUXNQV�fZNZUS|�V�[FM&fZYOv�V�fZNbU�|��2�(m_R`aR�V�[ TXR�P�dFYx[FP�R�UINZ`pR�PÖY*g�UImKR�V\vwUX]FV*f.MONQP�ÎpV*[ÐMÕUXm_R�PSNZ`�]_fQV�UIY\T2`#V�U�v�m UXY���NZUXm_NZ[ > �6D � Nb[#V*fbf�v�VxP�R�P���y[_dKTIR�MDNevwU�V�^_fZR } giTIY\`ãUIm_R�MONQP�ΪçèP��ONZR��t�ªm_Y{PSUBMDR�fQV�|KPqdÐV*TIUXNQV�fZfZ|�Vxv�vwY\]K[DUÖgiYxTUImKR�MDNåéªR�TXR�[FvwR{�û�TIRcV*UIR�TNZ[ÐP�NZsxmDU.v�V*[�^FR(Vxv�mKNZR��{R�M�^D|�vwY\`pdFV*TXNZ[_s�UXm_R2`aR�V\PS]_TIRcMtV*[FM�PSNZ`�]_fQV�UIR�M�TIR�PSdFY\[FPSR(UINb`aR�MDNQPSUITINb^_]_UXNZY\[ÐP� � ]_R�` � 8� °��æÖNbs\]_TXR�8K� � PSm_Y���PrMDNeP�UXTINZ^K]_UINbY\[FPtY*g�`aR�VxP�]_TXR�M�V*[FM8P�NZ`�]_feV*UIRcMÓTIRcP�dFY\[FPSRaUINb`aR�P(giY\TäVPIV�`ad_fbR��xV�fZNQMKV*UINbY\[��BY\TIÎOfZY�V\M�Y*g �?> � >T>B> TIR�n{]_R�PSU�P���LtP;��NbUIm�`aY�P�U�Y*gBY\]KTt�xV*fZNeM_V*UXNZYx[�TIR�PS]_fZUWPw�hYx[_R

Page 36: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5B7

Actual Simulation

|­0® |­

5¯ |­

10® |­

15¯ |­

20® |­

25¯ |­

30® |­

35¯ |­

40® |­

45¯ |­

50®|°0.00

|°0.25

|°0.50

|°0.75

|°1.00

Response Time (ms)

Fra

ctio

n of

Req

uest

s

(^]w_�`cb R±«�%�'*) � R�PSdFY\[FPSR#�(NZ`aR u NQPSUITXNZ^_]_UXNZYx[FPygiY\T�Vaý(V�fZNeM_V*UXNZY\[ú�úY\TIÎOfZY�V\M�²´³�µj¶¸·9¹�º2»I¼½¿¾2µj¶¼�¹�À2ÁI¹ÂjÃ�Äź�Æ(½�¾2µj¶zÆÈÇÊɺ�Æ�Ë�ÂIÇ2·9Ìlº�Æ(½ÎÍ�µ2µ2µ2µ¦¼�¹�É�Ã5Ç2·�Ï�º,·�Äк£Â"É�¹Ñ(½�Ò2Ó�ÔOÌ�¹�º£ÂS·9¹�À�ÁI¹�¼�ÃV¼�ÄÈÕ¹ËÖ¹�×ÊØgÇ2ÂI¹Â�Ã�Äк�Æ�Ñ�½Ùµ,Ú(Û�Û;Ìl¼7·9¹�À�ÁI¹�¼�Ã7ÄÈÂ�Ã5¹·kº,·9·�ÄÈÏ,º�ÆÜÃ�Ä�Ìݹ�Ë�ÁIÂjÄ.Þ�Ç2·5Ì�Ñ�ß

v�V�[�^FV*TXR�fZ|�P�R�R�UImFV�UUS�(Y�vw]KTI�{R�P.V*TXR�d_TIR�PSR�[OU��*� � ]_R�` � 8� _MDR�jF[_R�PÖUXm_R�TIY{YxU2`aR�V*[�PXno]FV�TIR�m_YxTINbÙ�Y\[OU�V�fMDNeP�U�V�[FvwR�^FR�US�(R�R�[ÓUXm_R�US�(Y�MDNeP�UITXNZ^_]KUINZYx[)vw]_TI�{RcP�V\P�V MDR�`aR�TINbUjFs\]_TXR�giYxTtMDNeP�Îa`pYOMDR�f�v�V*fZNb^_T�V�UINbY\[���(m_R�MDR�`aR�TINbU�jFsx]_TIRrgiYxTtUImKRr�xV*fbNQM_V�UINZYx[�TI]_[úPSm_Y���[�NZ[#jFs\]_TXR,8_� � NQP > � >HA `#Pw�F��m_Nev�m)NQP�fZR�PXP;UXmFV*[> � �X� Y*g.UXm_Rtv�Y\TITXR�P�dFYx[FMDNZ[Ks�`aR�V*[�TXR�P�dFYx[FP�R�UINb`aR{���(mKRt�(YxT�P�UXÏ°v�V\P�R�MDR�`aR�TXNZUÖjÐs\]_TXRtY\^FPSR�TI�{RcM´Y��{R�TV*fbf��xV*fZNeM_V*UXNZYx[ÓTX]_[FP���VxP(Y\[_fb| � � �X� Y*g�UIm_R�vwYxTITXR�P�dFY\[ÐMDNZ[_s�`aR�V�[#TIR�PSd5Yx[FP�R�UINb`aR{�

�ÔDdFR�TXNZ`aR�[OU�P2NZ[)UIm_NePtMDNQPXP�R�TXU�V�UINZYx[&]FPSRrUXm_R�×tz ~ 5B5�8 > fZNb[_R�Y*g�MDNeP�Î)MDTINb�{R�P�giY\T�UIm_TXR�R�TIR�VxP�Y\[ÐPw�æÖNbT�P�U��ÖUXm_R#P�Nb` ]KfQV*UXY\T�v�Y\TITXR�vwUXfZ|�`aYOMDR�fQPtUIm_RpY\^FPSR�TI�{R�M�^FR�mFV��ONZY\T�Y*g�UIm_RcP�RpMDTINb�{R�Pw���{R�vwYx[FMh�UXm_R�|mFV��{Rt`aY�P�UBY*g�UIm_R�V\MO�\V�[FvwR�M giR�V�UI]_TXR�P�MDR�PXvwTINb^FR�M NZ[ÕP�R�vwUXNZYx[�5O� � � � �2�(mKNZT�Mª�_MDR�UWV*NbfZR�MaPSdFR�vwNåj5v�V*UXNZY\[ÐPgiY\T�UImKRrMONQP�ÎKP(]FPSR�MaNZ[)P�Yx`aRtY*glUIm_R�UITWV\vwRcMÓPS|_PSUIR�`ÕP(V*TXR�]_[FV��xV*NZfeV*^_fbR{�

�(m_NQP�MDNeP�ÎúPS]_^FP�UXNZUX]_UINbY\[úfZR�VxM_PyUIY)US�(Y#PSNZs\[KNåjªv�V�[DU�MDNkÒ#v�]_fZUXNZR�P��ræÖNbT�PSU��hUXm_R ^ÐV\P�R�R�ÔOdFR�TINb`aR�[OU�V*fMDNeP�Î } UImKR#×tz ~ 5B5�8 A �ämFV\P�V�MDNkéªR�TIR�[OU�P�UXY\T�V�s\Ràv�V*dFVxvwNZUS|�UXmFV*[ÛUImKR#MDNQPSÎ_Pr]ÐP�R�M"^O|8P�Y\`pRaY*g�UXm_RUITWV\vwRcM�P�|KP�UIR�`#Pw�ó��Y¥^FR�UIUXR�Ta`#V�U�v�mßUXm_RúP�NbÙ�R&Y�grUXm_RúP�Nb` ]KfQV*UXR�MÛMDNQPSÎ_P�UIYÛUIm_Y�P�RúNZ[¢UIm_R�UXT�V\v�R�MP�|KP�UXR�`#P��5UXm_Rr[O]_`�^5R�T�Y*gBd_fQV�UIUXR�T�PyNePyTIRcvwY\[DjÐs\]_TXR�M&UIY#v�TIR�V�UIR�MONQP�ÎKPyfeV*TIsxR�R�[_Yx]_s\m�UXY&v�Y\[OU�V*Nb[&UXm_RV\v�UINZ�{R�MKV*U�Va��NbUIm_Yx]_UrR�ÔKvwR�PXP�Nb�{Rr]_[O]FP�RcM�`aRcMDNQVO�r�(m_NeP�NePy[_Y\U�]_[_TXR�V\PSY\[FV�^_fZR{��P�Nb[FvwR�Vad_TIYOMO]FvwUINbY\[fZNb[_RtY�gBMDNQPSÎ_P(Y�giUIR�[)MDNkéªR�T�P(Yx[_fZ|aNb[#UIm_R�[O]_` ^FR�TBY*g�d_fQV�UIUXR�T�P��â×tz � 5\VB ¾�

�(m_RBP�R�v�Y\[FM�V*[ÐM�`aYxTIR.NZ`adFY\TXU�V�[DUªNQPIPS]_R2NQPhUXmFV*U.×tz ~ 5B5�8 > MDNQPSÎ_P�PSR�TI�ONQvwR�TIR�n{]_R�PSU�PhV�UV�MONåéªR�TIR�[DUT�V�UIR�UImFV�[&UImKR�MDNeP�ÎKP;Nb[ÓUXm_R�MONQP�ÎpTIR�n{]_R�PSUyUXT�V\v�R�Pw����Y�d_TIYOMD]ÐvwRrm_RcVc�ONZR�T�Y\T�fZNZsxmDUXR�T��(YxTIÎOfZY�V\M_P��5UXm_RUITWV\vwRcMòNZ[OUIR�T�V*TXTINb�\V�f(UXNZ`aR�P�V*TXR�PIv�V*fZRcM³UXY"dKTIYOMD]Fv�R�V�T�V*[Ks\R&Y�g�`aR�V*[³V*TITXNZ�xV*f�T�V�UIR�P��ß��m_R�[ÛUXm_RPIv�V*fZRag¾VxvwUIYxT NeP´Yx[_R{�(UXm_R)P�NZ`�]_feV*UIRcM"NZ[OUIR�TWV*TXTINZ�xV�f(UINb`aR�P�`#V*UWv�mÛUImKY{P�R)UITWV\vwR�Mª�ò��m_R�[ßUImKR&PXv�V*fbRg¾V\v�UIY\T�NQP�U��BY_�FUIm_R�UXT�VxvwR�MÓNb[DUXR�T�V�TITXNZ�xV*f�UXNZ`aR�P�V�TIRävw]_U�NZ[&mÐV*fåg } MDY\]_^KfZNZ[KsaUIm_R�`aR�V�[&V�TITXNZ�xV*f.T�V�UIR\�W���{R�[#��NZUXm�V*[)NQMDR�[DUXNZUS|aPXv�V*fbNZ[_srg¾VxvwUIYxT��Fm_Y��(R��{R�T��DUXm_R��(YxTIÎOfZY{VxM_Py�BY\]_feMÓ]_[FMOY\]_^_UXR�MDfb|amFV��{R�^5R�R�[

Page 37: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5�8

MDNkéhR�TIR�[OU2Någ�UXm_R�PS|_PSUIR�`#P.UIT�VxvwR�M mÐV\M ^FR�R�[p]FP�Nb[_s�×tz ~ 5T5�8 > MDNeP�Î�MDTXNZ�{R�P�êoNb[DgiY\TX`#V*UXNZYx[aV�^5Yx]_U�m_Y��NZ[ÐMDNZ�ONQMD]ÐV*fFTIR�n{]_R�PSUBV*TITXNZ�xV*feP(MDR�d5R�[FM ]_dFY\[#d_TXR��ONZY\]ÐPlTXR�n{]_R�P�UBvwYx`ad_fbR�UINbY\[FPNQP[_YxU�d_TIRcP�R�[OU2NZ[�UIm_R�PSRUITWV\vwRcPw���(m_NePtNQP�V#vwY\`a`pY\[#d_TIYx^_fZR�`ø��NZUXm"UXT�VxvwR�ϾMDTINb�{R�[�PSNZ`�]_fQV�UINZYx[��F^_]_U�P�m_Yx]_fQM�[_YxU�Nb[D�xV�fZNQMKV*UIRUImKR�no]FV�fZNbU�V*UXNZ�{R�TIRcP�]_fbU�P�V*[FM�NZ[FPSNZsxmDUWPw�tL�fQP�YK�hUImKRrR�ÔOdFR�TINb`aR�[OU�P(MOTINZ�{R�[&^O|ÓUXm_Rrgi]_fbfPS|_PSUIR�`áUITWV\vwRcPs\R�[_R�T�V�fZfb| d_TXY��DNeMDR�vwY\TXTIY\^FYxT�V*UXNZ[_spR��DNeMDR�[Fv�R{�

Ä ÈFÈNO £Q¦Oà ` R ` R ] £ _�(m_R�PSNZ`�]_fQV�UIYxT�vwY\[OU�V�NZ[FPaV�[O]_` ^FR�T�Y�g�dFV*TWV*`aR�UXR�T�PrTXR�fQV�UIR�M¢P�dFR�vwNkjªv�V�fZfZ|úUIY³MDNQPSÎßv�Y\`a`#V�[FM

n{]_R�]_R�Nb[_s_�.�y[OgiY\TIUX]_[FV�UIR�fb|{�\V�`aR�UImKYOMDY\fbY\s\|tgiYxT�xV*fZNeM_V*UXNZ[_s�MDNQPSÎrv�Y\`a`#V�[FMtn{]_R�]_R�NZ[_s�`aYOMDR�fePhNQPÖ^FR�Ï|{Y\[ÐMrUIm_R�PXvwY\dFR�Y*gªUIm_NePMDNePIP�R�TIU�V�UINbY\[����m_R�[�V�v�V\v�m_R�ϾP�R�[FPSNZUXNZ�{RBV*fbs\Y\TXNZUXm_` NePÖ]FP�RcMr^D|äV�MONQP�ÎOÏi^FV\PSR�MPIv�m_R�MO]_fZR�T��_UIm_R�MDNeP�Î#`aYOMDR�f°çèP�v�V\v�m_R�NQP�d_TIYx^5RcMÓ^FRwgiY\TXR�P�R�fbR�vwUXNZ[_säV [_R��¼TXR�n{]_R�P�U(giYxT�P�R�TI�ONQvwR{�B�(m_NePTIR�d_TIR�PSR�[OU�P�VÓ`aYxTIR�V�s\s\TXR�PIPSNZ�{R#V�d_d_TXY{V\v�m¥UXmFV*[¥R�ÔDNeP�U�P�NZ[8vw]_TXTIR�[OU�MDNQPSÎDÏi^FV\PSR�M¥PXv�m_RcMD]_fZR�T�Pw����m_Nev�mUS|DdKNQv�V�fZfZ|�dKTIY\^FR#UImKR&v�V\v�m_R } giYxT�PIv�m_R�MD]KfZNZ[Ks&d_]_TXdFY{P�RcP���Y\[_fb|¥��m_R�[ÛV�TIRcno]_RcP�U�V�TITXNZ�{R�P3� ��V*TX| �x�  °��[FV*^KfZNZ[KsúvwY\`a`ÕV*[FM�n{]_R�]_R�NZ[_sàMDY{R�Pr[_YxU�VcéªR�vwU�UXm_Ra�xV*fb]_R�P�giY\T�UIm_RÕvwY\`a`ÕV*[FMúV*[FMÛvwYx`ad_fbR�UINbY\[Y��{R�TImKR�V\MadFV�T�V*`pR�UIR�TWPw�OV*fbUIm_Yx]_s\màP�Yx`aR�Y*g�UIm_R�Y��{R�TImKR�V\M_P(`ÕVc|�YOv�vw]_T�NZ[#dFV*TWV*fbfZR�f } MD]_R�UXY TXR�no]KR�P�U:IdKNZdFR�fZNb[_NZ[KsH<�V*U�UImKR�MDNQPSÎ5�W�2�ÔDdFR�TXNZ`aR�[OU�PNb[ÓUXm_NQP�MONQPIPSR�TIUWV*UXNZY\[)]FP�R�US�(Y�v�Y\`a`#V�[FM�no]_R�]_R�NZ[Ks�vwY\[_ÏjFsx]_T�V�UINZYx[FPw�FMOR�[_Y\UXR�M 2�b R�§?R�R�Ã)V*[FM (�` PwPS��(mKR�UXm_TIR�R�vwY\`pd5Yx[_R�[OU�PY*g�NZ[OUIR�TIÏiTIR�n{]_R�PSU(v�Y\[Fvw]KTITIR�[Fvw|NZ[#UXm_R�MDNQPSÎa`aYOMDR�f±V*TXR�dKTIR�PSR�R�ÎONZ[_sK�DTIRcV\Mam_NZUWP(]_[FMDR�Ty`aNePIPSR�Pw�OV*[ÐMÓ��TINbUIR�d_TXR�^_]DéªR�TXNZ[_sK�zTIR�PSR�R�ÎONZ[_s

L;giUIR�TVtMONQP�ÎtjF[KNQP�mKR�PqUXm_R(`pR�MDNQV�Vxv�vwR�PXPqgiY\T�VyTXR�no]KR�P�U��*NbUÖUXT�V*[ÐP giR�TWPV*[O|rTXR�`#V*Nb[_NZ[Ks�v�Vxv�m_RcMrM_V�U�VUIY�UImKR�mKY{P�U } Nb[#UIm_R�v�VxP�RrY�g2V�TIRcV\MÓTXR�n{]_R�P�U��BV*[FM#dFR�T�giYxTI`#PBvwfZR�V�[D]KdhÝ�vwYx`ad_fbR�UINbY\[�d_TIYOvwRcPIP�Nb[_s_��L;UUImKRrPXV*`aR�UXNZ`aR{�{UXm_R�MDNeP�Î#v�V*[&^FR�sxNZ[àV*[O|a`aR�v�mFV*[KNQv�V�f5dFY�P�NZUXNZYx[_NZ[_spTIR�n{]_NZTXR�M´giYxTyUXm_R�[_R�ÔOUyTXR�no]KR�P�UNZ[�UImKRyYx[_ÏØ^FY�V*T�M)no]KR�]_R{���(m_NQPNQP2MDR�[_Y\UXR�MaV\P*Á b R�§?R�R�à ] £ _ �.ë(Y\UXmazTXR�P�R�R�Î�V*[FMaæ_]_fbf_R�ÔOdFR�TINb`aR�[OU�V*fvwYx`a`#V*[ÐM¥no]KR�]_R�Nb[_s¥v�Y\[DjFsx]_T�V�UINbY\[FP#V*fbfZY��÷d_TXR�P�R�R�ÎDNb[_s_�§Ü°[�UImKR�V*^ÐP�R�[Fv�R&Y*g�dFR�[FMONZ[_s¥TXR�n{]_R�P�UWPw�MDNeP�ÎKP(U�|Od_Nev�V*fbfZ|�d_TXRwgiR�U�v�m#PSR�no]KR�[DUXNQV�f�M_V�U�V�NZ[OUIY�UImKR�Yx[_Ïi^5Y�V*TWM�v�V\v�m_R�VcgiUXR�T�V´TXR�V\MaTXR�no]KR�P�U��� R�V\M#×yNbU�P��y[FMOR�T��&NQPXP�R�P

�(m_R�æ_]_fZf.vwYx`a`#V�[FM n{]_R�]KR�NZ[_sävwY\[OjFs\]_TWV*UXNZY\[úV�fZfbY*��P(TXR�V\M#TIR�n{]_R�PSU�P2UImFV�Uym_NbU�NZ[#UImKR�Yx[_Ïi^5Y�V*TWMv�Vxv�m_R�UIY�^FR#PSR�TI�ONQv�R�M&NZ[¥dÐV*T�V�fZfbR�f2��NZUIm³V*[O|"Yx[_s\YxNZ[_s�`aRcMDNQV#V\v�vwR�PIP��&�(mKR�TIR#V�TIRaUXm_TIR�R giY\TX`#PtY*g© ] ¤�§ ` £Q¦cR b�ÈF] §G§?R�§(R�[FV*^_fbR�M�NZ[�UIm_NeP�v�Y\[DjFsx]_T�V�UINbY\[��BæÖNZTWP�U��{V*[O| [KR��ßTXR�V\M�TIR�n{]_R�PSU2��m_Y{PSR�M_V*UWV�NePR�[OUINbTIR�fb|�vwYx[DUWV*NZ[KR�M NZ[#UXm_RtY\[KÏØ^FY{V�T�M)v�V\v�m_R } V Â�` PSP b R O ¦F© ] ¤x�NQP�PSR�TI�ONQv�R�M´Nb`a`aR�MDNQV�UIR�fb| } ��NZUXm_Y\]KUV*[O|�NZ[OUIR�TX�{R�[_NZ[KsrMONQPIv�Y\[_[_RcvwUw�.giY\fZfbY��(R�M�^D|pV*[O|�[_R�vwR�PXPIV�TI|pvwfZR�V�[D]KdhÝ�vwYx`ad_fbR�UINbY\[�V\v�UINZ�ONZUS|{��{RcvwY\[FMª�V*[O|#[_R��§TIR�VxMÓTXR�no]KR�P�U���m_Y�P�R�jFT�PSUtPSR�vwUIYxTyNeP�vwY\[OU�V�NZ[_RcMÓNZ[#UXm_R�v�V\v�m_R } V�Á OÇb ¤ ]wO P b R O ¦�© ] ¤\�2��NbfZfmFV��{R(UXm_R�V��xV*NbfQV�^_fZR�M_V*UWVyUITWV*[FP°giR�TITXR�M�UXYtUIm_R�mKY{P�U�d_TINbY\T.UIY�MDNePIvwYx[_[_R�v�UINZ[Ks_�.�(m_NZTWMh�\��m_R�[_R��{R�T.VtMONQP�ÎMDNePIvwYx[_[_R�vwUWP�giTIYx`øV�^_]FP��_NZUWP(d5R�[FMDNZ[Ksan{]_R�]_R�NeP�P�R�V�T�v�m_R�M giY\T�TIR�VxMÓTXR�no]KR�P�UWP(UImFV�UymFV��{R:XR�[_Yx]_s\m�<Y*glUIm_R�NbTyTXR�n{]_R�P�UXR�M#M_V*UWVaV��xV*NZfeV*^_fbR�NZ[&UXm_R�v�V\v�m_R�UIY���V*TXT�V�[DUtTXR�vwYx[_[_R�vwUXNZYx[&V�[FM�P�]K^FP�R�n{]_R�[OU�M_V�U�VUITWV*[FP°giR�T } V*[ ] £a¤�R b�È R�¦ ]wO ¤ER b R O ¦0© ] ¤x���t�(mKRr�xV*fb]_R�Y*g :IR�[_Y\]_sxm�<aNQP�MDR�UXR�TI`aNb[_R�Ma^O|ÓUXm_R�ë(]OéhR�Tæ_]_fZf � V*UXNZY_�OVxP�P�dFR�vwNkjFR�M�^D|�UXm_R�� ~ �OÜd5R�TINZdKm_R�T�V�fF^_]FP�dKTIY\UXYOvwY\f � � ~ �oÜ � 7B °���(m_RtTIRcno]_RcP�UBvw]_TXTIR�[OUIfb|dFR�T�giYxTI`aNb[_s�`aR�MDNeV Vxv�vwR�PXPtV*fb��V�|_P�mFV\Ptd_TXNZY\TXNZUS|#Y��{R�TtNZ[OUIR�TI`aR�MONQV*UXRtTIRcV\M&m_NbU�Pt��m_R�[�^_]ÐP�VxvwUINb�DNbUS|NQP(TXR�n{]_NZTXR�Mh�

Page 38: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5 �

�úTINZUXR�zTIR�^K]DéªR�TINb[_s�(m_R�æ_]_fZfªvwYx`a`#V*[ÐM n{]_R�]_R�NZ[_sävwY\[DjÐs\]_TWV*UINbY\[àV*fZfbY���P(V�MDNeP�ÎaUXY�UIT�V�[FP giR�T�V*fbf�Y\T�dFV�TIU�Y�g2Vr��TXNZUIR

TIRcno]_RcP�U�ç PyMKV*U�V#UIYaUXm_R�Y\[KÏØ^FY{V�T�M¥v�V\v�m_R�NZ[�dFV�T�V�fZfZR�fÖ��NbUImúV*[O|�Y\[Ks\Y\Nb[_s#`aR�MDNeV Vxv�vwR�PXP } NkgBUIm_R�TXRrNePV*[üV*d_dKTIY\dKTINQV�UIR)v�Vxv�m_R)PSR�s\`aR�[DU�V��xV*NZfeV*^_fbR\���8�(m_NQPrNeP�MDR�[_YxUIR�MÛVxP�Á b RD3 `Há R b�] £ _ �¥Ü°[ÛV\MKMDNZUXNZY\[±���m_R�[KR��{R�T�V�MONQP�Î8MDNePIvwYx[_[_R�vwUWP�giTIYx` V&^_]FP���NbU�PrdFR�[FMDNb[_sún{]_R�]_RaNeP�P�R�V�T�v�m_R�M�giYxT���TINbUIRaTXR�no]KR�P�UWPUImÐV*U�v�V*[�^5R�V\PIPSNZsx[_R�M UXYrV�[#V��xV*NZfeV*^_fbRtPSR�s\`pR�[DU.Y\TBmFV��{R�:XR�[_Yx]_s\m�<�P�dFVxvwR�V��xV*NbfQV*^KfZR�NZ[�UImKR�NZTBv�Vxv�m_RP�R�s\`aR�[OUrUXY¥��V�TITWV*[OU TXR�vwY\[K[_R�vwUXNZY\[¢V�[FM�P�]_^ÐP�R�n{]_R�[OUaMKV*U�VúUIT�V�[FP giR�T } V*[ ] £a¤ER b�È R�¦ ]SO ¤�RNÆ b�] ¤�R© ] ¤\�W�ó�(m_R��xV*fb]_R�Y*g¬:IR�[_Y\]_sxm�<òNePaMDR�UXR�TI`pNZ[_R�Mú^D|¢UIm_Rúë(]DéªR�Tp�`ad_US| � V�UINbY_��V\P#P�dFR�v�NåjFR�Mß^O|UImKR � ~ �OÜ(dFR�TXNZd_mKR�T�V�fÖ^_]ÐPyd_TIYxUIYOvwYxf=� � ~ �OÜ � 7� ¾���(m_RrTXR�no]KR�P�U�vw]_TXTIR�[OUIfb| dFR�TSgiY\TI`pNZ[_s�`aRcMDNQV�Vxv�vwR�PXPV*fb��V�|KP(mFV\P�d_TINbY\TXNZUS| Y��{R�T�Nb[DUXR�TI`pR�MDNbV*UXRy��TXNZUIR�m_NZUWP(��m_R�[&^K]FP�V\vwUXNZ�ONZUS|�NQP(TIRcno]_NbTIR�Mª�

��m_R�[ävwY\`a`ÕV*[FMtn{]_R�]KR�NZ[_s�NePqR�[FV*^_fbR�Mh��UXm_R�MDR�g¾V*]_fbUÖYx[_ÏØ^FY�V*T�M�v�V\v�m_R�vwYx[DjFsx]_T�V�UINZYx[rNePq`aYOMONåjFR�MUIY�NZ[FvwTXR�V\PSR2UIm_RB[D]_`�^FR�T�Y*g5v�V\v�m_RBP�R�sx`aR�[OU�P��Öæ_YxTÖR�ÔOdFR�TINb`aR�[OU�PF��NZUImKY\]_U�vwY\`p`#V*[FM�n{]_R�]_R�NZ[_sK�*R�Vxv�mY\[KÏØ^FY{V�T�M#M_V�U�V�v�Vxv�m_R�v�Y\[OU�V*Nb[FP�US�BY�5 � C�Ï°PSR�vwUIYxT } � 5BD���ëy�.P�R�s\`aR�[OU�P��\Y\[KfZ|�Y\[_R�Y*g.��m_Nev�m�NQP]FPXV*^_fbRgiY\Tp��TINZUXR&TXR�no]KR�P�U#MKV*U�VO� É æ_Y\TaR�ÔOdFR�TINb`aR�[OU�Pr��NbUIm�v�Y\`a`#V�[FMÛno]KR�]_R�Nb[_s_��R�Vxv�m¢Y\[_Ïi^FY{V*TWM¼v�Vxv�m_RvwYx[DUWV*NZ[ÐP5giY\]_T � 5TD*ϾP�R�vwUXY\T } C�8���ëy�ªP�R�sx`aR�[OU�Pw��V*fbfZY���NZ[_s�sxTIR�V�UIR�T.NZ[OUIR�TIÏiTIR�n{]_R�PSUhv�Y\[Fvw]KTITIR�[Fvw|�V�UÖR�Vxv�mMDNeP�Ϊ��L `#V*ÔONZ`�]_`�Y*g�U��BY)P�R�sx`aR�[OU�P�v�V*[ú^FRaMDNbTIUS| } Nkg(dKTIR�^_]OéhR�TINZ[KsÓ��TXNZUXR�M_V*UWVo�����ÔOd5R�TINZ`pR�[DUWPNZ[¢UIm_NeP MONQPIPSR�TIUWV*UXNZY\[�dFYxNZ[OUaY\]_UpUIm_RàP�R�[FPSNZUXNZ�ONZUS|"Y�gäPIv�m_R�MD]_fbR�T�dFR�T�giYxTI`#V�[FvwR#UIY8Y\[_Ïi^FY{V*TWM¼v�Vxv�m_RvwYx[DjFs\]KT�V*UXNZYx[��hV�fZUXm_Y\]_sxm�Vrgi]_fZf±P�UX]FMD|#Y*glPIv�m_R�MD]KfZR�T�Ý�v�Vxv�m_R�NZ[OUIR�TWV\vwUXNZY\[pNQP(fZR�giU�giY\T�gi]_UX]_TIR��(YxTIΪ�

³��g­ ï + �2-&� + �����L PS`#V*fbf�[D]_`�^FR�T(Y�gBUIm_R�R�ÔDdFR�TXNZ`aR�[DUWP�]FPSR�P�|O[OUIm_R�UXNQv�V�fZfb|DÏis\R�[KR�T�V�UIR�MaMONQP�Î#TXR�no]KR�P�U�UITWV\vwR�P��5dKTINZÏ

`#V�TINZfb|&UXY�V*fbfZY���vwYx`adFV*TXNQPSY\[ú��NZUIm8d_TIR��ONZYx]FP��BY\TXÎh�)�(m_RaTXR�`#V*Nb[FMDR�T�]FP�RaUXT�VxvwR�Prv�V*d_UX]_TIR�M�giTIY\`V\v�UI]FV�frPS|_PSUIR�`ÕPw�ã×yR���fZR�UIUIϾzVxv�ÎxV*TWMßV�[FM u Nbs\NZUWV*f��2n{]_NZdK`aR�[OU ~ Y\TIdFYxT�V*UXNZYx[>mÐVc�{R�dKTIY��DNeMDR�M¢P�NZÔR�ÔOUIR�[ÐP�NZ�{RpUIT�VxvwR�PrY�g�MDNQPSÎ¥TIRcno]_RcP�U�V\v�UINZ�ONZUS|�giTIYx` �xV�TINZYx]FP�vw]FP�UXY\`aR�T�V*[ÐMòTIRcP�R�V�T�v�mßPS|_PSUIR�`ÕPw�ÛÜ°[V\MKMDNZUXNZY\[±�DPS|_PSUIR�`�V�[FM�MDNQPSÎ�V\vwUXNZ�ONZUS|r��V\PUITWV\vwR�M�Y\[ÕV*[p� ~ � �(YxTIÎKP�U�V�UINbY\[aUXY�R�[FV*^_fbRyR�ÔDdFR�TXNZ`aR�[OU�P]FPSNZ[_s�UIm_R�d_TXYOvwR�PXP�ÏtªFY��¼m_Y{PSUy`pYOMDR�f°�

§ ? · ?�¸ »¼G�½o¾á¤�<�ây9�<Q½OC�£�7 R :�<Q½�(m_R8P�NZÔ§×�z÷V*[FM u � ~ UITWV\vwRcPÓV�TIRÛMOR�PIvwTXNZ^FR�MßYx[_fZ|�^_TXNZR«ªÐ|�V\P#UIm_R�|�mFV��{R�^5R�R�[¼MONQPIv�]FPIPSR�M

R�feP�R���m_R�TIR&Nb[ß`aYxTIRàMDR�U�V�NZfâ� � ]_R�` � 7\� � V*`#V � 5� °�¼�(mKR�UIT�VxvwR�MÛ�(Y\TXÎDfbY{VxM_P#P�dFV�[¼V"^KTIY{VxMßT�V�[_s\RY*g�R�[D�ONZTXY\[_`aR�[DUWPw�ªV*[FM"RcV\v�m"UXT�V\v�RaNQP�V*U�fZR�VxP�U�VÕgi]KfZf2�(YxTIÎKP�m_NkgiU } DÓm_Yx]_T�P��tNb["fbR�[_s\UXm��#�.V*^_fbR8_�U5d_TXY*�ONQMOR�P�P�Yx`aRt^FVxP�NQvtNb[DgiY\TX`#V*UXNZY\[pY\[&RcV\v�mÓUXT�VxvwR{�

�(�(YÛY*g�UXm_R�UITWV\vwR�P�vwYx`aRÓgiTXY\` ×�R���fZR�UXUIϾzV\v�ÎxV*TWMßP�|KP�UXR�`#PrTX]_[_[_Nb[_sÛ×tzϾ�yÿ��BV"�{R�T�PSNZYx[�Y*g�t�tÜ°ÿ�� � ]_R�` � 7« °�Zd�egfhfji&vwYx`aR�PygiTIYx` V�PSR�TI�{R�TrV�U�×yR���fbR�UIUXÏ°zVxv�ÎxV�T�Mú��V*^FY\TWV*UIYxTINbR�P } zV*fbYúLyfZUXY_�~ L��B]FP�RcMÕgiY\T�d_TXY\s\TWV*` MDR��{R�fZY\dK`aR�[OU��OP�Nb` ]_feV*UXNZY\[±�D`#V�NZf°�OV�[FM&[_R���P�� kmlon�p e�NeP�giTXY\` VrjFfZR�P�R�TI�{R�TV*U�UImKRr��[_NZ�{R�TWP�NbU�|�Y�g ~ V�fZNkgiY\TI[KNQVD�Fë(R�TIÎ{R�fbR�|{�\]FPSR�MÓdKTINZ`ÕV*TINbfZ|rgiYxT�vwY\`adKNZfQV�UINbY\[#V�[FMÓR�MONZUINb[_s_���mKNZfZRUImKR�P�RaUXT�VxvwR�P�V*TXR#V\vwUX]FV*fbfZ|úUS�(Y&`pY\[OUImFPtNZ[úfZR�[_s\UXm��ÖUXm_RaR�ÔOdFR�TINb`aR�[OU�P�NZ[¥UXm_NQP�MDNQPXP�R�TXU�V*UXNZYx[¥]FP�RÕVP�Nb[_s\fbR��(R�R�ÎOÏifZY\[Ks�P�[FV�dFP�m_YxU } � ÝE7 > Ý � 5aUIY3CoÝECoÝ � 5o�W��V\P�NZ[ � �"YxTIU � 8F� � ]_R�` � 7? °�

�(m_R#Y\UXm_R�T�giY\]_T�UXT�V\v�R�P�V*TXRÕgiTXY\` vwYx`a`aR�TWv�NeV*fý2L�ÿ÷PS|_PSUIR�`#P�TI]_[K[_NZ[_súUImKRÓý��"��Y\dFR�TWV*UINb[_sP�|KP�UXR�` � � V*`#V � 5? °�Zq�rts�uwv=xGz´NePägiTXY\` V�UIT�V�[FPIVxvwUINbY\[�d_TXYOvwR�PXP�NZ[Ks¥R�[O�DNbTIY\[K`aR�[OU�Nb[Û��m_NQv�m�V�^5Yx]_UÊ�q�Ï�Í6Õ�Í6ÕmÎwÏ�Ó�Ü�ÔgÐ?ã?òþÔ«ÑÌÎSã�ÒwÓ�Òkã Õ�Ø?ÓÌòþÔ�ã�ß6Î&ÑÀÛJÐ,äTÖ«ã�Ò�Ô�ÎSÍ6ÛJÐyòhÛ«ÒmÎwÏ�Ó*æ�åæ��ç�çè,�*Ø?Í6Õw×�Ø?ÒwÍUé«ÓJå

Page 39: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5BC

�hR�[Ks\UIm �&R�V*[ � R�n �qYxU�V�f � R�V\M �{R�n � R�V\M�qTWV\vwR } m_Y\]KT�P�� u NQP�ÎKP � R�no]KR�P�UWP ��NZÙ�R } ��ëy� zÖR�T�v�R�[DUWV*sxR zÖR�T�v�R�[DUWV*sxR~ R�fbfZY � CTD D 7D�65TCB5O�6DB5�8 CD�U7 8HCO� >X� 5D� �X���[FV*Î{R � CTD 7 � � � 7B7O�6CBCT7 CD� A � 5O�98 � � DD�6C �LyNZTXÏ � P�� � � C 5D� �G> CO� A�> 8 � � � A�� �67 � A �UD ��OvwNZϾ�y� ��� �6C 8 7 � � � D A �6C � 7 5D�V8 D � � �X� � 7D�6D �Þ�TWMDR�T � 5 5T5 � 5D�U5B7BCO�98 7B7 7D� � DBCO�65 � A � �X�� R�dFY\TXU D 5T5 DD�6C A�� � >\�HA 7D� � DBDO�6C � 7D�UD �

��O 3cPSR±«�%F#&)�×�zßV*[ÐM u � ~ u NeP�Î � R�n{]_R�PSU���T�V\v�R ~ mFV�T�V\v�UIR�TXNQP�UXNQv�P

�B>T> UXT�V��{R�f�V�s\R�[OU�Pa`#VxMDRúV*NbTIfZNb[_R�V�[FM m_YxUIR�f�TIR�PSR�TI�xV*UXNZYx[FPw� km{ r|u?} k NeP giTIY\` VÛPXvwNZR�[OUINkjªvÓUXNZ`aR�ÏP�mÐV*TINb[_s�R�[O�DNbTIYx[_`aR�[OUTI]K[_[_NZ[Ks�V*[FV�fZ|OUINQv�`aYOMDR�fbNZ[_s�P�Y�giUS��V*TXR�V*[ÐMÓs\TWV*d_mKNQv�V�f�V*[ÐMÓPSU�V�UINQPSUINev�V*fªdFV\v�ÎDÏV*sxR�Pw� ~^s°��eJstV�[FMNv�eÌ�ÇiHs���V*TIR�giTIY\` VÓ`ÕV\v�m_NZ[_R�dÐV*TIUWPrMDNeP�UXTINZ^K]_UINbY\[ÛvwYx`adFV�[D|{� ~^s°��e�s���vwY\fbfZR�vwUXR�MMD]_TXNZ[_s�MKVc|OUINb`aR�m_Y\]_TWPw�FTIR�dKTIR�PSR�[DUWP(V�[&Y\TWMDR�T�R�[OUITX|aV�[FMÓdKTIYOvwR�PXP�Nb[_s �BY\TXÎDfbY{V\Mª��v�eÌ�ÇiHsg�Ø�KvwY\fbfZR�vwUXR�MV*U�[_Nbs\mOU��DTXR�d_TXR�P�R�[OU�P�Vr^ÐV*U�v�m#R�[O�DNbTIY\[K`aR�[OU�sxR�[_R�TWV*UXNZ[_s�TXR�dFY\TIUWP;Y�g2UImKRrMKVc|ªçèP�VxvwUINb�DNbUINbR�Pw�

§ ? · ? · Xt9;W9W�¡éZ=½DC_<7\ £�7 R :�<c½�qY�MOTINZ�{R�UImKRtd_TIYOv�R�PIPSÏ ªFY��¼mKY{P�U�`pYOMDR�f°�OPS|_PSUIR�`ÚV\vwUXNZ�ONZUS|���VxP(UITWV\vwR�M�Y\[)V*[)� ~ � 7�8 7B7��(Y\TXÎDÏ

P�UWV*UXNZY\[¢vwYx[DUWV*Nb[_NZ[_sàV�7B7ú��×yÙpÜ [OUIR�f�D > 8 DBC"`aNevwTIYxd_TIYOv�R�PIPSY\T�V*[FM´8 D"��ëóY*g�`#V*Nb["`aR�`aY\TX|{�#LP�Nb[_s\fbRt×�z ~ 5T5�8 A MDNeP�Î�MDTXNZ�{R�P�R�TX�DNevwR�M�V�fZfhY�g.UIm_R�MDNeP�Î�TIR�n{]_R�PSU�PNZ[aRcV\v�m UXT�V\v�R{�2æ_]_fZfªP�|KP�UXR�` UITWV\vwRcP�(R�TIR�v�V�d_UI]KTIR�M ]ÐP�NZ[Ks�V*[#NZ[FPSUITX]_`aR�[OUIR�Mr�{R�T�P�NbY\[aY�gUXm_Rr�{ý � 8ä��zß�t�tÜ°ÿ�Yxd5R�T�V*UXNZ[_spP�|KP�UXR�`�UImFV�U��TINbUIR�PtUXNZ`aR�PSU�V�`adFR�MÓR��{R�[DU�MKV*U�V#NZ[OUIY)V&MOR�MDNQv�V*UIRcM�D#��ë>Î{R�TI[_R�f�`aR�`aYxTI|a^_]OéhR�T��#�(m_RaNb[FP�UXTI]_Ï`aR�[OU�V�UINbY\[�NQP]_[_Yx^_UITX]FP�Nb�{R{�DNb[FvwTIRcV\P�Nb[_srUXm_R�MD|D[ÐV*`aNev;Nb[FP�UXTI]FvwUXNZYx[avwYx]_[OU(^O| fbR�PIP2UImFV�[ > � ��� Nb[ UXm_R�(YxT�PSUtv�VxP�R } VxPIPS]_`aNZ[Ks�UImFV�U�UIm_R�UITWV\vwR�^_]OéhR�TtvwYx]_fQMa[_YxUy^FR�Y\UXm_R�TX��NQP�R�]FPSR�M5�W�

�qTWV\vwRcP��(R�TIRpv�V*d_UX]_TIRcM�giY\T�U��BY�MDNkéªR�TIR�[OU�US|DdFR�PtY*g��BY\TXÎDfbY{V\MKPw��d�iH�y�msge°xgxtTXR�d_TIRcP�R�[OU�P�V&PSNZ[_Ïs\fbR¢7 > � A ��ë jFfbR�^5R�NZ[_sÛv�Y\`ad_TXR�PIPSR�MòUXY �?> � A ��ët�(�(m_R ka�Bl v ��e l UXT�V\v�R�Pav�V�d_UI]_TXR�UIm_RúVxvwUINb�DÏNZUS|ÛY*gäUIm_R¥��|D[ � û�R�[§PS|D[OUImKR�UINevÕjFfbR�TIRwgiR�TXR�[FvwR)s\R�[KR�T�V�UIY\T �â�l^KfZN � 8� °�tv�Y\[DjFsx]_TIRcMÁUXY¥R�`�]_fQV�UIR�V�[R�MDNbUwÝ�`#V*Î{R\ÝcMDR�^_]Ks�R�[D�ONZTXY\[_`aR�[DU.��NZUXm#VrdFV*TWV*`aR�UIR�TXNZÙ�R�Mr[O]_`�^FR�TY*g�]FPSR�T�P��2��Vxv�mp]FP�R�TBdFR�T�giYxTI`#PBVP�R�TINZRcP(Y*g�T�V*[ÐMDY\` :IUWV\PSÎ_P�< NZ[OUIR�[ÐMDR�M UXY�P�NZ`�]_feV*UIR�R�MDNbUINb[_s_�FvwYx`ad_NbfZNZ[Ks_�{V�[FMÓR�ÔOR�vw]KUINZ[Ks�jFfbR�Pw�

�(m_R2UITWV\vwR2^_]DéªR�T.PSNZÙ�R�fZNZ`pNZU�P_UXm_R2fZR�[_sxUIm�Y*gKUImKR(� ~ � UXT�V\v�R�Pw�.ý�R�TI|�fZNZsxmDUª�(YxTIÎOfZY{VxM_P�U�V*Î{RlP�R��{R�TWV*fm_Yx]_T�P�UIY�jFfZf�UXm_R�^_]DéªR�T��_^_]_U�V*TIR�]_[KNZ[OUIR�TXR�P�UXNZ[_srgiYxT�MDNQPSÎ#PIv�m_R�MD]KfZNZ[Ks�TIR�PSR�V*TWv�m��2×�R�V��D|��(YxTIÎOfZY{VxM_Pn{]_NQv�ÎDfb|�jÐfZf�UImKR&^_]DéªR�T���d_TIR��{R�[DUXNZ[_s)UIm_Ràv�V*d_UX]_TIR)Y*g¬:�v�Y\`ad_fbR�UIRE<&V*dKd_fZNev�V*UXNZY\[üV\vwUXNZ�ONZUS| } N°� R��Z�V�fZfd_mFVxP�R�P�Y*g;V*d_d_fbNQv�V�UINbY\[�R�ÔOR�vw]_UXNZYx[h����L�P�VaTXR�P�]_fbU��hUXm_R�UIT�VxvwR�P�vwY��{R�T�fZNbs\mOUIÏiUIY\Ïi`aR�MONZ]_`á�(YxTIÎOfZY�V\M_P���{Nb[FvwR�`aR�MONZ]_`aÏiUIYxÏØmKR�V��D|¥�BY\TXÎDfbY{V\MKPÓ^FR�[_RwjÐUÓUXm_Rú`aY{PSU giTIYx` V*s\sxTIR�PXP�Nb�{R¥MDNeP�ΧPXv�m_RcMD]_fZNb[_s_��UXm_RdFR�T�giYxTI`#V�[FvwR)NZ`ad_TXY��{R�` R�[{U�PrTIR�d5YxTIUXR�MògiY\T#R�ÔOdFR�TINb`aR�[OU�P�]ÐP�NZ[KsòUXm_Rú� ~ � UITWV\vwRcPaV*TXR"UXm_R�TIR�giY\TIRvwYx[FP�R�TX�xV*UINb�{R{�

Page 40: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5 A

³��°¯ $&%B')����!�����)� �Ñ��� + �(��2'�® ��(m_NQPBP�R�v�UINZYx[aMOR�PIvwTXNZ^FR�PUImKRy�xV*TXNZYx]FP(PXv�m_RcMD]_fZNb[_s�V*fbs\Y\TXNZUXm_`#P2vwY\`pdFV*TXR�MrNZ[�UIm_R�giY\fZfbY���NZ[_s�v�mFV*d_Ï

UIR�T�Pw�Fv�V*UIR�s\Y\TXNZÙ�RcM ^D|pUIm_R�US|DdFR�Y*g�NZ[OgiY\TI`ÕV*UINbY\[#]FPSR�Ma^D|aUXm_R�V*fbs\Y\TXNZUXm_`#Pw�

§ ? � ?�¸ ¡�:hE�<cº�9;WSGIH�J��üG°C5E�N_H;]�A(7^\ R C_GSA;H�]�7_A�\ �Ö68<�WSA����Ü°[aUIm_NeP(MDNePIPSR�TIUWV*UINbY\[��KPIv�m_R�MD]KfZNZ[KsrV�fZsxY\TINbUIm_`ÕP�UImÐV*U(]ÐP�RtmFV�T�MD��V*TXR�Ï°PSdFR�vwNåj5vyÎD[KY*��fbR�MDsxR�V*TXRtdFV*TXÏ

UINbUINbY\[_R�M�^D|�UIm_R�fbR��{R�f\Y�gFNZ[OgiY\TI`ÕV*UINbY\[äMDR�U�V�NZf¾��PIv�m_R�MD]KfZNZ[Ksy^FVxP�R�M�Y\[���ë��tP�Y\[KfZ|{�{PXv�mKR�MD]_fbNZ[_s�sxNZ�{R�[äVgi]_fbf_��ë��yÏiUIYxÏ°z2ë��Û`#V*d_dKNZ[_sK�\V�[FM�PIv�m_R�MD]KfZNZ[Ksy��NbUIm�gi]KfZfOÎD[_Y���fbR�MDs\R } Nb[FvwfZ]ÐMDNZ[_s�v�]_TITXR�[DU.TIRcV\M5Ý���TINZUXRm_R�VxM&dFY{P�NbUINbY\[���v�Y\`a`#V�[FM Y��{R�TXm_R�V\MKPw�ªv�V\v�m_R�v�Y\[OUIR�[OU�P��_R�U�v\�k���tÞ�[_fZ|)PXv�m_RcMD]_fZR�T�P(��NZUXm&gi]_fZf�ÎO[_Y���fZÏR�MDsxR�mFV��{R�P�]DÒÕvwNbR�[DU�NZ[OgiY\TI`ÕV*UINbY\[)UIY#R�[FV�^_fZR�V�fZs\YxTINbUIm_`#P�UImÐV*U�TIR�MO]FvwR�Y��{R�T�V�fZf.dFY{P�NbUINbY\[_Nb[_s#UINZ`pR�P} N¾� R{�b�OvwY\`�^_NZ[KR�M PSR�R�Î#V�[FMÓTXY\UWV*UINbY\[FV�fÖfeV*UXR�[FvwNbR�P��W�

�ÔDdFR�TXNZ`aR�[OU�P&��NbUIm ��+,� GW3 O §?R�¦áV�[FM Â�` PwP�G ÈFO Á�PIv�m_R�MD]KfZR�TWP"vwYx`adFV�TIR��_�O��æ(� ~ Ï°�ÖÞ�Þ�����ÖÞ�Þ��´�{ýr� ~ Lt� } > �65{�I�OV�[FMaæ ~ æ�� } giYxT(TIR�giR�TIR�[ÐvwR(d_]KTIdFY{PSR�P��W�2�lÔOdFR�TINb`aR�[OU�P���NZUXm´gi]_fbfZÏi`#V*däPIv�m_R�MDÏ]_fbR�T�P(]FPSR�V´m_R�]_TINeP�UINevyUIYpP�R�fZR�vwUB^FR�US�(R�R�[pTIR�n{]_R�PSU�P(UIY�UImKRrPXV*`aR�d_mD|KP�Nev�V*f±vw|OfZNZ[ÐMDR�T����(m_R�m_R�]_TXNQPSUINQvNQP�^FVxP�R�M#Y\[&UXm_R ~ Ͼ�ÖÞ�Þ�� V�fZs\YxTINbUIm_`áUIY�U�V�Î{R�V\MD�xV*[OU�V�s\R�Y�g2UIm_Rä×tz ~ 5B5�8 A çèPyd_TXRwgiR�UWv�m_Nb[_s�v�Vxv�m_RV*[ÐM"UIY)TIR�MD]ÐvwR�UIm_R�[O]_` ^FR�T�Y*g�m_R�VxM"PS��NZUWv�m_RcPw�aL gi]_fbfZÏi`#V*dúPXv�m_RcMD]_fZR�T�PIV�UINQP°jFR�P�V*fZf2TXR�no]KR�P�UWP�Yx[UImKR�vw]_TXTIR�[OU�UITWV\v�Îa]FPSNZ[_s ~ Ï°�ÖÞ�Þ����5UXm_R�[àV*fZf�TXR�n{]_R�P�UWP(Y\[�UXm_R�vw]_TITXR�[OU�vw|DfbNZ[FMOR�T(]FPSNZ[_s ~ Ï°�ÖÞ�Þ����V*[ÐMÓUImKR�[#UIm_R�V*dKd_TIYxd_TINeV*UIRäP�R�R�ÎDÏiTIR�MO]FvwNZ[Ks�V*fbs\YxTINZUXm_`÷UXYaPSR�fZR�v�U(UImKR�[KR�ÔDU�v�|DfbNZ[FMDR�T�UXYaPSR�TI�ONQv�R{�

�ÔDdFR�TXNZ`aR�[OU�Pt��NbUIm Â�` PwP�GgÃ�£cÄXÆ�PSR�¦ _ R�PIv�m_R�MO]_fZR�TWP�]FPSR��Oz2��æ>V�[FMßV�v�V\v�m_R�ϾP�R�[FPSNZUXNZ�{R��{R�T�PSNZY\[Y*g��Oz2��æÁUXR�TI`pR�M # ©QÄ b ¤�R�§«¤ 2 Ä�§ ] ¤ ] Ä�£ ] £ _ê� ÆÅ O ¡�©cR �¬� ]wÈ R (^]Sb §«¤¬� �úY\TXU � 8H ¾���(m_Ra�Oz ~ ��æV*fbs\YxTINZUXm_`ãV\PXP�]_`aRcP�V;dFY{PSNZUXNZY\[KNZ[_stUXNZ`aR.Y*gÐÙ�R�TIY�giY\T�V*[O|�TIR�VxM�TXR�no]KR�P�U�UXmFV*U.��NZfbf{m_NZU�Nb[�UXm_R(Yx[_Ïi^5Y�V*TWMv�Vxv�m_R��.-

§ ? � ? · ¡�:hE�<cº�9;WSGIH�J��üG°C5E�N_H;]�A(7^\ R C_GSA;H�]�7_A�\ ���U rAc¿(<���(m_R�R�ÔDdFR�TXNZ`aR�[DUWP5NZ[�UXm_NQP2MDNePIPSR�TIUWV*UINbY\[�R�ÔOd_fbY\TIR�Y��{R�TWV*fbfOP�|KP�UIR�` dFR�T�giYxTI`#V�[FvwR�RwéªR�v�U�PÖY�gh�xV�TINZYx]FP

V*fbs\YxTINZUXm_`#P��NZUXmaV�[FM ��NbUIm_Yx]_U(R�ÔOd_fbNQvwNbUPS|_PSUIR�`aÏifZR��{R�fDNb[DgiY\TX`#V*UXNZYx[�����NZUImKY\]_U�P�]Fv�m Nb[DgiY\TX`#V*UXNZYx[��OVPIv�m_R�MO]_fZR�T�çèP(Yx[_fZ|#TIRcvwY\]_TWP�R�NQP�UIYpTIR�MD]ÐvwR�UIm_R�d5Y�PIPSNZ^_NbfZNZUS|aY�g�P�U�V�TI�xV*UXNZYx[&giY\T�m_NZsxm&d_TXNZY\TXNZUS|aTXR�no]KR�P�UWP^O|"`aNb[_NZ`�NZÙ�Nå[KsaTIR�PSdFY\[FPSRÓUXNZ`aR��xV�TINQV�[FvwR } N°�âR{�Z�.TIR�MD]ÐvwNZ[_s)PSU�V*TX�xV*UINbY\[¢NZ[¥sxR�[_R�TWV*fØ�W��æ_Y\T�UIm_NePrd_]_TIÏdFY{PSR{�2V*[¢V*sxR�Ïi�(R�Nbs\mOUIR�Mò�oz���æ V*fZsxY\TXNZUImK` NePrV*feP�YúPSUI]FMDNbR�Mh� �4#&2�� (����Y� NQP�R�n{]_NZ�xV*fbR�[OU�UXY&UXm_RL��OL2��æÛV*fbs\YxTINZUXm_`÷d_TXY\dFY{PSR�M&NZ[ �â�{V\vwY �D�  °�ë/#L��Oz2��æ } �¼�BV\M*ùS]ÐP�U�P�R�V\v�m#d5Y�P�NbUINZYx[_NZ[Ks UXNZ`aRtdKTIR�MDNevwÏUINbY\[ }�ìsíïî�ð ��^D|ÛPS]_^_UXT�V\v�UINZ[Ks"UXm_R#�(R�Nbs\mOUIR�M¥V�`aY\]K[DU�Y�gtUXNZ`aRaUXm_R#TIR�n{]_R�PSUrmFVxP´^FR�R�[ß��V�NZUXNZ[_s&giYxTP�R�TI�ONQvwR }9ñ òóì^ôÙõ5öa÷ ���2L�PXv�mKR�MD]_fbR�T]FPSR�PUIm_R�TIR�PS]_fZUXNZ[_s�RwéªR�v�UINZ�{RBdFY{P�NbUINbY\[_Nb[_srUXNZ`aR }�ì¿ø(ù�ù �.UIY�P�R�fbR�vwUUImKR�[KR�ÔDU�TXR�n{]_R�P�UBUIY�NQPXP�]_R{�

ì¿ø(ù�ùVúUìsíî´ðHû�}9ñ òüì^ôÙõ5ö.÷ ��(m_R�V*sxR�Ï°PSR�[FPSNZUINb�{R�V*fbs\YxTINZUXm_`�TIR�vwYx`a`aR�[ÐMDR�MrNZ[ � �{V\v�Y �D�  ªNQP(R�n{]_Nb�\V�fZR�[OU2UIY�L��oz���æ } CD�U7o�W�2�(m_R

�_ R�¦ # ©QÄ b ¤�R�§«¤ 2 Ä�§ ] ¤ ] Ä�£ ] £ _ý� ÆÅ O ¡�©QR �F� ]wÈ R (^]Sb §«¤�V�fZsxY\TINbUIm_`à����m_Nev�m¢vwYx` ^KNZ[_R�P�V*sxR�Ï3��2å*�¿q�6�ÑÌßjÔgÕSÕwÍ0äTÓ�ÕmÔQÒSÓ°ÔJØ�ÒSÓ�<Jã�Ó�ÕSÎ�ÔgÕ�ÔQÏ�Í6ÎoÍVòHÎSÏ�Ó*äTÒwÕSÎ�ÒwÓk<«ã�Ó�ÕwÎSÓ�ØyÕSÓ°ÑÌÎSÛ«Ò�Í6ÕÇÒwÓ�ÕSÍjØ?Ó�ÐGÎ�Í6Ð*ÎwÏ�ÓcÑ�Ô«ÑSÏ�Ó�ÛJÒoÍ6Õ ÑÀã�ÒSÒwÓ�Ð?ÎSß6Ý

ÚBÓ�Í6Ð�Ö�òhÓ�ÎÌÑSÏ�Ó�ØyòhÒwÛJÜFÎwÏ�Ó�Ü=Ó�Ø?ÍjÔ�å=�q�Ï�Ó�cÎ�,c*q�6,Ô�ß6ÖJÛJÒwÍ6ÎSÏ�Ü�ä&Ô�Õ&ÑwÏ�Û«ÕSÓ�Ð�Í6Ð�ÕSÎwÓ�ÔJØyÛ�ò�ÎSÏ�Ó�ËS�,q�6�Ôgß6Ö«ÛJÒSÍ6ÎwÏ�Ü´ÕSã�Ö«ÖJÓ�ÕwÎSÓ�ØyÍ6Ðþ���?Ó�ß6Î�ÿ��5�HÚTÓ�Ñ�Ôgã�ÕwÓ�ËS�,q�6Í6Õcß6Ó�ÕwÕôÕwÓ�Ð�ÕwÍUÎwÍ6éJÓ�ÎSÛ�ØEÍ��HÓ�ÒwÓ�ÐTÑÌÓ�Õ%ÍUÐ�á�ÒSÓ�ØEÍ ÑÀÎSÓ�Ø�áBÛJÕwÍUÎwÍ6ÛJÐ�Í6Ð�Ö^ÎwÍUÜyÓ�Õ�ä�Ï�Ó�Ð,ÑÌÛ«Ü=áTÔ�ÒSÍ6Ð�Ö�ÒSÓk<«ã�Ó�ÕwÎSÕ�ä�Ï�ÛJÕSÓ�ä�ÔgÍ6ÎSÍ6Ð�Ö^ÎwÍUÜyÓ�ÕÔgÒwÓ�Ð�Ó�ÔgÒQÎSÏ�Ó�Ô�ÖJÍ6Ð�Ö�ßUÍ6ÜyÍUΰå

Page 41: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5BD

P�R�[FP�NbUINZ�ONZUS|üV*[FMóv�Vxv�m_R�Ï°PSR�[FP�NbUINb�DNbU�|��;NeP�V*feP�YßNb[Fvwfb]FMDR�M Nb[ UXm_R¥R�ÔOdFR�TINb`aR�[OU�P��áæÐYxT�V�PS]DÒ#v�NZR�[OUIfb|fQV�TIsxR��ó�_^FYxUIm�L��Oz2��æ } �¼��V*[FM#L��oz ~ ��æ } �¼��MDR�s\R�[_R�T�V�UIR�NZ[OUIY�æ ~ æ��F�

/ R J ` R�§«¤ b�] ¤ ] ¡ O P ] ¤�4 � £ Â Ä b�ÈFO ¤ ] Ä�£�(m_R�v�fQV\PXP�Nkjªv�V*UXNZYx[�PIv�m_R�`pRaNZ[OUITXYOMD]FvwR�M¥Nb[ � û�V�[_s � 7X �NeP´]FPSR�M³giYxTaPS|_PSUIR�`pÏØfbR��{R�f2dFV*TXUINbUINZYx[_NZ[Ks

Y*g�TXR�no]KR�P�UWPw� ��]SÈ R G ¡ b�] ¤ ] ¡ O P�TIRcno]_RcP�U�P�v�V�]FP�R)d_TIYOvwRcPIP�RcP UIY¥Nb`a`aR�MONZV�UIR�fb|���V�NZU } Y\TÕ3QPSÄ�¡�ÃÖ��giYxTMDNeP�ÎÛPSR�TI�ONQvwR�� ��]SÈ RIGg£cÄ�£Q¡ b�] ¤ ] ¡ O P2TIR�n{]_R�PSU�P�MDYú[_Y\Upv�V�]FP�R)d_TIYOvwRcPIP�RcP´UXY"^_fbYOv�Ϊ�^_]_U�`�]FP�UäP�UINbfZf^FR#P�R�TI�ONQvwR�M�NZ[8Y\T�MOR�T�UIY�]_dªM_V�UIR#UImKRaY\[_ϾMDNeP�Î8vwY\dO|"Y�gtUXm_R#M_V�U�V�V�[FM"giTIR�Ra]KdÛP�mFV�TIR�M¥TXR�P�Yx]_T�vwRcP} R�� s_�b�Ö`#V�NZ[ú`aR�`aYxTI|F��� ��]SÈ R G P ]SÈ´] ¤�R�¦¥TIR�n{]_R�PSU�P�^5RcvwY\`aR�UXNZ`aR�Ï°vwTXNZUXNQv�V�fÖ]_[KfZR�PXPrP�R�TI�ONQvwR�M���NZUXm_NZ[UImKR�vwY\TXTIR�PSd5Yx[FMDNb[_s&UXNZ`aR�fZNb`aNZU����(m_R�V*dKd_TIYxd_TINeV*UIRpvwfeV\PIPSNåjªv�V*UINbY\[�giY\T�VaTXR�no]KR�P�UtNePyÎO[_Y���["^O|&UXm_RP�|KP�UXR�`áPSY*giUS��V�TIR�UImFV�UysxR�[_R�TWV*UXR�P(NZU��

�qY#R�ÔOd_fbY\NZU�TIRcno]_RcP�U�vwTINbUINQv�V*fZNbUS| Nb[DgiY\TX`#V*UXNZY\[±�hV#PIv�m_R�MO]_fZR�T�v�V*[�`#V�NZ[OU�V*Nb[�PSR�dFV*TWV*UXR�no]_R�]_R�P;giYxTTIRcno]_RcP�U�P���NZUXm¥MDNkéªR�TIR�[OU�d_TINbY\TXNZUINbR�Pw�#�(mKR±#*àÑPIv�m_R�MD]KfZR�TWP�]ÐP�R�M"Nb[¥UImKNQPrMONQPIPSR�TIUWV*UXNZY\[8d_fQVxvwR UXNZ`aR�ÏfZNb`aNZUXR�M#V*[FM�UINb`aR�ϾvwTINbUINevwV�f�TIR�n{]_R�PSU�PyNb[¥Vam_Nbs\múd_TINbY\TINbUS|&n{]_R�]KR�V*[FM�UINb`aR�Ïi[_Y\[Fv�TINZUXNQv�V�f�TIR�n{]_R�PSU�PyNb[VafZY��ód_TINbY\TXNZUS|)no]_R�]_R{� 5XW PIv�m_R�MD]_fbR�T�P�V*fb��V�|KP�R�`ad_US|aUImKR�m_NZsxm�d_TINbY\TINbUS|&n{]_R�]KR�^5R�giY\TIR�PSR�TI�ONQv�NZ[_sTIRcno]_RcP�U�PygiTXY\`0UImKRafZY�� dKTINZYxTINbU�|àno]KR�]_R{�pæÐYxT�PSNZ`ad_fbNQvwNkUS|{�_^FY\UXm¢no]_R�]_R�P�V*TXRaPXv�m_RcMD]_fZRcM&]FP�Nb[_s&UXm_RPIV�`aR�PXv�m_RcMD]_fZNb[_s�V*fbs\YxTINZUXm_` } R{� sK�Z�o5HW ~ Ͼ�ÖÞ�Þt�r�W�

§ ? � ? � ¡�<�ây9�<H2C_G R W�¡(C_7K< R \ M TyCKG�\ G9{ R C_GSA�H=½LóPIv�m_R�MD]_fbNZ[_s�V�fZsxY\TINbUIm_` v�V�[#^5R�Y\d_UXNZ`aNbÙ�R�M�UIY�NZ`adKTIY��{RydFR�TSgiY\TX`#V*[Fv�R�giYxT�P�R�n{]_R�[OUINeV*f�TXR�no]KR�P�U

P�UXTIR�V�`#Pw� � R�n{]_R�PSU ¡HÄa£c¡ O ¤�R�£ O ¤ ] Äa£§vwYx` ^_Nb[_R�PtY\[KRaY\T�`aYxTIRpP�R�n{]_R�[OUINeV*f2TIRcno]_RcP�U�P�NZ[OUIYàV�P�NZ[Ks\fZRfQV�TIsxR�T TXR�n{]_R�P�U��>Þ�[_RàvwY\`�^_NZ[KR�M¥TIR�n{]_R�PSU Nb[Fvw]_TWP´fbR�PIP�TIR�n{]_R�PSU dKTIYOvwR�PXP�Nb[_sÛV*[ÐM�vwY\`a`�]_[_Nev�V*UXNZYx[Y��{R�TImKR�V\MÛUImFV�[ßUImKR&UIYxU�V�ftY��{R�TIm_RcV\M¥R�ÔOd5R�TINZR�[FvwR�M¥^O|ßPSR��{R�TWV*f�P�R�dFV*TWV*UIR�TXR�n{]_R�P�UWPw��L vwY\`�^_Nb[_R�MTIRcno]_RcP�U(`ÕVc|�V�fQPSY�NZ[Fvw]KT�fZR�PXP�TIYxU�V�UINZYx[FV*f�feV*UXR�[Fvw|{�KP�Nb[FvwRtUXm_R�TIR�NQP�[KYaMDR�fQV�|�^FR�US�(R�R�[pUIm_R�`aR�MONQV�V\vwÏvwR�PXP�R�P�giY\TUXm_R�vwY\`pd5Yx[_R�[OUÖTXR�n{]_R�P�UWPw�Þ�[�UIm_R�YxUIm_R�TmFV*[ÐMh�{[_Y\[_R�Y�g�UXm_R(Nb[FMDNZ�ONQMO]FV*fOTIR�n{]_R�PSU�Pv�V*[�^FRTIR�d5YxTIUXR�M&VxPyvwYx`ad_fbR�UIRt]K[DUXNZfhUXm_RrR�[DUXNZTIR�vwY\`�^_NZ[KR�M TIRcno]_RcP�U�mFVxP;^FR�R�[àP�R�TX�DNevwR�Mh�2�(mKNQP�`#V�| Nb[�ªªV*UXRUImKR�TXR�P�dFYx[FP�RBUINZ`pR�PÐgiYxT.P�Y\`pRY*gFUXm_RBvwY\[OUITXNZ^_]KUINZ[Ks�TIR�n{]_R�PSU�Pw�.LyfeP�YK�*TXR�no]KR�P�U±vwY\[Fv�V*UIR�[FV*UXNZY\[�TIR�n{]_NbTIR�PUImKR�V*^_NbfZNZUS|#UIY#dFR�TSgiY\TI`�PIv�V�UIUXR�TwÝ�s{V*UXm_R�T u ��Lr� _ ÞyUXm_R�TX��NQP�R���V*[úVxM_MDNZUXNZYx[FV*f2`aR�`pY\TI|OÏiUIY\Ïi`aR�` YxTI|vwYxdD|)`#V�|&^FR [KR�vwR�PXPIV*TX|&UXY&`aY��{R�UIm_R�TIRcno]_RcP�UIRcM�M_V*UWVÓUIY#YxT�giTXY\`ÑV#P�Nb[_s\fbR dKmD|KP�Nev�V*fbfZ|)vwY\[OUINbs\]_ÏY\]ÐP�TIR�s\NZYx[¥Y*g�`pR�`aY\TX|{���(m_R#PS]DÒaÔ % / MDR�[_Y\UXR�PrvwYx[Fv�V�UIR�[FV�UINbY\[¥Y�g�P�R�n{]_R�[OUINeV*fTXR�V\M"TXR�n{]_R�P�UWPw�V*[ÐMÓUImKR�P�]OÒaÔ¬% �� MOR�[_Y\UXR�P�vwY\[Fv�V*UIR�[FV*UXNZY\[)Y*gBPSR�n{]_R�[OUINQV�fh��TXNZUIR�TXR�no]KR�P�UWP } R{� sK�Z�5�K�O��æ(� ~ � V*[FM�ÖÞ�Þ��´� ~ �ó� ~ � ���

# R J ` R�£�¤ ]wO P^§?¡�©QR�¦ ` P ] £ _ Y�g�P�R�n{]_R�[OUINeV*f�TIRcno]_RcP�U�P�UITXR�V*`ÕP;Nb`aNZUWV*UIRcP ~ Ï°�ÖÞ�Þ��÷PIv�m_R�MO]_fZNb[_s Yx[V�P�`#V�fZfZR�T(PXv�V*fbR{�2�tPSNZ[_s�UXm_NQP(Yxd_UINb`aNZÙ�V�UINbY\[��OV�PIv�m_R�MD]_fbR�T(Yx[_fZ|ÕP�R�TX�DNevwR�P�UXm_R�:Im_RcV\M_P�< Y*glP�R�n{]_R�[OUINeV*fP�UXTIR�V�`#P } NZ[ÐvwfZ]FMONZ[_s#PSUITXR�V*`#P�vwYx[FP�NeP�UINb[_s#Y*g;VaP�Nb[_s\fbR�TIR�n{]_R�PSUw����L P�UXTIR�V�` :Xm_R�V\MÇ<ÕNePtUIm_R�TXR�no]KR�P�U��NZUXmrUXm_R�PS`#V*fbfZR�PSU.P�U�V�TIUXNZ[_s���ë��r�xæÐYxTÖR�Ô_V�`ad_fZR���V*[ �K�O��æ�PIv�m_R�MD]KfZR�T���NbUImrUXm_R�PSR�n{]_R�[OUINQV�fOPIv�m_R�MD]KfZÏNZ[KstY\d_UXNZ`aNbÙ�V*UXNZYx[t��NZfbf_PSR�fZR�v�U�UIm_R�P�UITXR�V*`¼:Xm_R�V\MÇ<�UXmFV*U���NZfZf{Nb[Fvw]_T.UImKR�P�mKY\TIUXR�P�UlP�R�R�Î�UXNZ`aR{�±�(m_R�P�]DgiÏjFÔ¡% #Q#&/ MDR�[_YxUIR�P.P�R�n{]_R�[OUINeV*f�PIv�m_R�MD]_fbNZ[_s�Y�gFTIRcV\M�TXR�n{]_R�P�UWPw�xV*[FM�UIm_RBPS]DÒaÔ¡% #Q#m� MOR�[_Y\UXR�P.P�R�n{]_R�[_Ïb���Ô�ÒSÖ«ÓôØ�Ô�Î�Ô%ÎSÒ�Ô�Ð�Õtò|Ó�ÒSÕQÚTÓ�Îtä�Ó�Ó�Ð�ÜyÓ�Ü=Û«ÒSÝ*Ô�ÐTØ^ß6Ûgä�Ó�Òmß6Ó�é«Ó�ß6ÕmÛ�òÇÎwÏ�Ó�ÕSÎSÛ«Ò�Ô�ÖJÓ�Ï�Í6Ó�Ò�Ô�Ò�ÑwÏ?Ý=ÔgÒwÓôÎtÝ?á�ÍjÑ�Ô�ß6ßUÝ�ÏTÔ�ÐTØ?ß6Ó�Ø^Ú?Ý

Ô��Lrhìgë2v�ñ��ë,h,îBì���Lv�v�ëEê°ê�Ó�Ð�ÖJÍ6Ð�ÓJå�qoÛ�ÏTÔgÐBØ?ß6Ó�ÒSÓk<«ã�Ó�ÕSÎ�ÑÌÛJÐBÑ�ÔgÎwÓ�ÐTÔgÎwÍ6ÛJÐ�ÙBÎSÏ�Óé>� Vc�ÏTÔgÒÌØ?ä�ÔgÒSÓ%Ü^ã�ÕSÎ�ÚBÓ*ÔgÚ�ßUÓ�ÎwÛØ?Ý?ÐTÔ�Ü=ÍjÑ�Ôgß6ß6Ý=ÒwÓ�Ø?Í6ÒSÓ°ÑÌÎ Ô ÕSÎSÒwÓ�ÔgÜ0Û�òçØ�Ô�Î�Ô�ÎwÛ�ÛJÒ�òhÒwÛJÜ�ÎSÏ�Óyá�Ï?ÝGÕwÍjÑ�Ôgß6ß6Ý�Ø?Í6Õ�ÑÌÛ«ÐGÎwÍ6ÖJã�Û«ã�Õ�Ü=Ó�Ü=ÛJÒwÝ=ÒwÓ�ÖJÍ6ÛJÐ�Õ*ÑÌÛJÐ?ÎÌÔgÍ6Ð�Í6Ð�ÖÎSÏ�ÓôÍ6ÐTØEÍUé?ÍjØ?ãTÔ�ß ÑÀÛJÜ=áBÛJÐ�Ó�Ð?ÎSÕ�Ûgò�Ô^ÑÌÛJÜ^Ú�ÍUÐ�Ó�Ø�ÒSÓk<«ã�Ó�ÕSÎ�å

Page 42: Aggressive Centralized and Distributed Scheduling ofDisk Requests

5 �

UINeV*f2PXv�mKR�MD]_fbNZ[_saY�g���TINbUIR�TIRcno]_RcP�U�P } R{�âs_�Z�.�_�O��æ(�k�_� � V*[ÐM"�ÖÞ�Þ����å�_�{�ó�k�_� � ����L�PIv�m_R�MO]_fZR�T�`#V�|mFV�[FMDfZR�PSR�n{]_R�[OUINQV�fDTXR�V\M�V*[ÐM´��TXNZUIR�PSUITXR�V*`#P.��NZUIm�MONåéªR�TIR�[DUYxd_UINb`aNZÙcV*UINbY\[FP } R�� s_�b�o�K�O��æ(� ~ �ó�k�_� � ���

³���³ õ �y��(�%��æ_Y\T.R�ÔDdFR�TXNZ`aR�[DUWP5]FPSNZ[_stUXm_R�PSNZ`adKfZRm_Y�P�U.`aYOMDR�f¾�*UXm_R(`pR�V*[�MDNeP�Î�TIR�n{]_R�PSU�TIR�PSdFY\[FPSR�UINZ`pR } VxvwTIY�PIP

V*fbf�PSNZ`�]_fQV�UIR�M�MDNQPSÎ_P��2NQP(UXm_R�d_TINb`#V*TX|�`aR�UITXNQv�]FP�RcMpgiYxT�vwY\`pdFV*TXNZ[_s��\V�TINbY\]FP�PIv�m_R�MD]KfZNZ[Ks�V*fbs\YxTINZUXm_`#PV*[ÐM"PXv�m_RcMD]_fZR�TyNb`ad_fZR�` R�[OU�V�UINbY\[FP��t�(m_RpPIn{]FV*TXR�M�vwY{RwÒÕvwNbR�[DU�Y*g��xV*TINeV*UXNZY\[ }�� -����&-w�yY�gBTIR�n{]_R�PSUtTIR�ÏP�dFYx[FP�R¥UXNZ`aRcP´NePÓV�fQPSYßTIR�d5YxTIUXR�Mh�tVxPÓNb[ � ��R�Y\T A 5B °�÷û�NZ�{R�[§Vòv�Y\[FPSU�V*[OU&`pR�V*[�TXR�P�dFY\[ÐP�RúUINZ`pR{��VMDR�v�TIR�VxP�R�NZ[�UImKRtvwY{R�Ò#vwNbR�[OUY*g±�\V�TINeV*UINbY\[aNb`ad_fbNZR�PhTXR�MD]FvwRcMrTIR�PSd5Yx[FP�R�UINZ`pR(�xV*TXNQV*[ÐvwR } N°�âR{�Z�\Nb`ad_TXY*�{RcMP�UWV*TX�\V�UINbY\[¥TXR�P�NeP�U�V�[FvwR\�W� � R�MO]FvwNZ[Ks&PSU�V�TI�xV*UXNZY\[³v�V*[úNZ[FMONZTIRcvwUIfb|ÓNb`ad_TXY*�{R�PS|_PSUIR�`0dFR�TSgiY\TI`ÕV*[FvwR�^O|TIRcMD]FvwNb[_s�UIm_R�dFY{PXP�Nb^_NZfbNZUS| Y�g2m_Nbs\m#d_TINbY\TXNZUS| TXR�n{]_R�P�UWP(NZ[Fv�]_TITXNZ[_s�R�ÔKvwR�PXP�Nb�{Rtn{]_R�]_R�NZ[_s�UINZ`pR{�

æ_Y\TrR�ÔDdFR�TXNZ`aR�[OU�P�]FPSNZ[_s)UIm_RadKTIYOvwR�PXP�ÏtªFY�� mKY{P�U�`aYOMDR�f¾�.P�R��{R�TWV*fBV*dKd_fZNev�V*UXNZY\[KÏ°PSd5RcvwNåjªv�`aR�UXTINev�PV*TXR)V*fQPSY"]KUINZfbNZÙ�RcMh�úæÐYxT¢d�iH�y�ms�e°xgx��.UIm_R)PSNZ`�]_fQV�UIY\T�TIR�dFYxTIU�PrUXm_R)V*d_dKfZNQv�V*UINbY\[ÛTI]K[òUXNZ`aR } N¾� R{�b�ÖUXm_RR�feV*dFPSR�M&UINb`aR�Y*g�UXm_R�vwYx`ad_TIRcPIP�NbY\[�d_TXYOvwR�PXP����äæÐYxT km�Bl v ��e l �qNbUyTXR�dFY\TXU�P�UXm_R�`aR�V�[&R�feV*dFPSR�M&UINb`aRgiY\T�UImKR�Nb[FMDNb�DNeMD]FV*f�]ÐP�R�T,:XU�V\PSÎ_P�< } N¾� R{�b�DUXm_R�`aR�V*[3¤ O §?Ã�¡HÄ È ÁcPwRH¤ ] Ä�£ ¤ ]wÈ R_���Ü°U�V�fQP�Y�TIR�d5YxTIUWP;UXm_R`aR�V�[´£cÄ�£HG ¡HÄ È Á ` ¤�R�¤ ]SÈ R5����m_Nev�mús\Nb�{R�PrPSY\`aR�NZ[FMONQv�V�UINZYx[¥Y*g�UXm_R#V�`aY\]_[OU�Y*g�UINb`aR�R�V\v�m¥UWV\P�ÎP�dFR�[ÐM_P(��V�NZUINb[_s�Y\[)MDNeP�ÎpV\vwUXNZ�ONZUS|{�.�(m_R�fQV�UIUXR�T(`aR�UITINev(NQP�vwYx[FP�R�TI�xV*UXNZ�{R{�{m_Y��(R��{R�T��OV\P(NbU(NeP(Y\^_UWV*NZ[KR�M^O|úP�]_^_UXT�VxvwUINb[_s&UXm_R feV*TXs\RpvwY\`adK]_U�V�UINZYx[úMDR�feVc|KP } R{�âs_�b��vwY\`pd_NZfbRrUINb`aR�V�[FM"R�ÔOR�vw]KUINZYx[�UINb`aR\�2giTIY\`UImKR�UWV\PSÎ&v�Y\`ad_fbR�UINbY\[�UINb`aR�Pw� u R�feVc|KP�V\PXP�YOvwNeV*UXR�M&��NZUXmÓ��V*NbUINZ[Ks�Y\[�PSmFV*TXR�MÓdKTIYOvwR�PXP�YxTyTXR�P�Yx]_T�vwRcP;YxT]FPSR�T�V\vwUXNZ�ONZUS|pV*TIR�PSUINZfbfhdFV�TIU�Y*g�UIm_R�`aRcV*[a[_Yx[_ϾvwY\`adK]_UIR�UINb`aR{�

Page 43: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��� ��� ö ñ>/ �

���������2�´����y��� $&%(')����!��*��)� ��� �2')� � + ���

~ R�[OUIT�V�fZNbÙ�R�M�PIv�m_R�MO]_fZNb[_stNZ`pd_fZNbR�PhUImFV�U�V�P�NZ[Ks\fZR�R�[DUXNZUS|�V�fZY\[Ks�UXm_R�ÜWÝxÞ�dFV�UImaNeP�VxvwUINb�{R�fZ|�TXR�Y\TWMDR�TIÏNZ[KsÓdFR�[ÐMDNZ[_s#TXR�no]KR�P�UWPw�aÞ�UIm_R�T�R�[DUXNZUXNZR�PydÐV*TIUXNQvwNbdFV*UXR�NZ[8MDNQPSÎ�PXv�m_RcMD]_fZNb[_saYx[_fZ|�^O|&R�ÔOUITWV\vwUXNZ[_sÕV*[FMdFVxPIP�Nb[_s#]FP�R�gi]_fNZ[OgiY\TI`ÕV*UINbY\[)UIYaUXm_R�V\vwUXNZ�{R�PIv�m_R�MO]_fZR�T����(m_R�m_Y�P�U�V�[FM�UXm_R�MDNeP�Î)V*TXR�R�Ô_V�`aNZ[KR�M#V\PdFY{PXP�NZ^KfZR�fZYOv�V�UINZYx[FPygiY\T�V#vwR�[OUITWV*fZNbÙ�R�M)PIv�m_R�MD]_fbR�T���ë(Y\UXm�dFY{PIPSR�PIP�V#PSNZs\[KNåjªv�V�[DU�no]FV�[DUXNZUS|#Y*g�]FP�Rwgi]KfNZ[OgiY\TI`ÕV*UINbY\[����2V\v�mÓfbYOv�V*UXNZYx[&mFVxPyvwR�TIU�V�NZ[)V\MO�\V�[DUWV*sxR�PyV�[FM&MONQPIVxMD�xV*[OU�V�s\R�P��

Lòm_Y�P�UXÏØ^FVxP�R�M�PIv�m_R�MO]_fZR�T.mFVxPÖR�V\PS|�V�[FMrNZ`a`pR�MDNeV*UXR2V\v�v�R�PIP�UIY�PS|_PSUIR�`pÏØfbR��{R�f�NZ[DgiYxTI`#V�UINbY\[��.Ü°UÖmÐV\PUImKR;giTXR�R�MDYx` UIY�TIR�YxT�MDR�T�UXm_R�R�[DUXNZTXR�P�R�U2Y*g±Y\]_UWP�UWV*[FMDNb[_s�TIRcno]_RcP�U�P��OV*[FM UXm_R�d5R�[FMDNZ[Ks�TXR�n{]_R�P�UBn{]_R�]_RfZR�[_s\UXmÓNeP;fbNZ`aNbUIR�MrYx[_fZ|#^O|aUImKRrV�`aY\]K[DU�Y�g2`#V*Nb[a`aR�`pY\TI|��ÖL¼m_Y�P�UXÏØ^FVxP�R�M�PXv�mKR�MD]_fbR�T�v�V�[&dFR�TSgiY\TI`vwR�TXU�V�NZ[ÛPXv�m_RcMD]_fZNb[_s#Y\d_UXNZ`aNbÙ�V*UXNZYx[FPw��P�]Fv�mÛV\PrTXR�n{]_R�P�UävwY\[Ðv�V*UXR�[FV*UXNZYx[���UXmFV*U�V�TIRa[KY\U�dFY{PXP�NZ^KfZR } YxTmFV��{R�fZNZUXUIfbR�^5R�[_RwjFU��ÖgiY\T�MDNQPSÎDÏi^FVxP�R�M#PIv�m_R�MO]_fZR�TWPw�2Þy[pUIm_R�Y\UXm_R�T(mÐV*[FMh�_mÐV*T�MO��V*TXR�ϾP�dFR�vwNkjªvyNZ[OgiY\TI`ÕV*ÏUINbY\[)` ]FPSU(^FRrR�ÔDUXT�V\v�UIR�M)V*[FM#UIT�V�[FP�`pNZUIUXR�M UXY#V´mKY{P�UXÏØ^ÐV\P�RcM�PIv�m_R�MD]_fbR�T��Bæ_Y\T�UIm_R�`aY{PSU�V*sxs\TIRcPIP�Nb�{RPIv�m_R�MO]_fZNb[_s�V�fZs\YxTINbUIm_`#P } R{� sK�Z���Oz ~ ��æ�����UXm_R2TIR�n{]_NZTXR�MtVxv�vw]_TWV\vw|�V�[FM�no]ÐV*[OUINZUS|�Y*gFmÐV*T�MO��V*TXR�ϾP�dFR�vwNkjªvNZ[OgiY\TI`ÕV*UINbY\[a`ÕV*Î{RtUXm_NQP�V�MDNåÒÕvw]_fbU(UWV\P�Ϊ�BLyfQPSY_�_PS|_PSUIR�`ÕP(��NZUIm)vwR�[DUXT�V*fbNZÙ�RcM´m_Y�P�UXÏØ^FVxP�R�M�PXv�mKR�MD]_fbR�T�Pv�V�[_[_Y\U#UWV*Î{R&gi]_fbf�V\MD�xV�[DUWV*s\R8Y*g�UIm_RúNZ[OUIR�TIÏiTIR�n{]_R�PSUavwYx[Fvw]_TXTIR�[Ðvw|ßY�éhR�TIR�Mß^O|�vwYx`a`#V�[FMDϾno]_R�]_R�MMDNeP�ÎKPw�

Ü°[aUIm_NeP�v�mÐV*d_UXR�T��{UImKR�vwR�[OUITWV*fZNbÙ�R�M�PIv�m_R�MD]KfZR�T2TIRcP�NQMOR�P(V�U(UImKR�mKY{P�U } R{� sK�Z�{��NZUXm_NZ[pUIm_RrÞ�Ýx�aMOR��DNevwRMDTXNZ�{R�TWP����Û�(mKR&R�ÔOdFR�TINb`aR�[OU�P�V*TXR&dFV�TIUINbUINbY\[_R�M¥^FVxP�R�MßYx[ßUXm_R#U�|OdFR&Y�g�NZ[DgiYxTI`#V�UINbY\[¥]FPSR�Mò^O|¥UXm_RPIv�m_R�MO]_fZR�T��

��?� $&%B')����!�����)� �ø���' MÖ� ,{+ ��® ���� + � �&� + ® µ��÷��� + ��¶

� ?�¸(?�¸ ¡[ZtH2CFE�<�C_GS: @ A(7o¾�WSA R º�½L÷P�`ÕV*fZf2[O]_`�^5R�T�Y�gtR�ÔDdFR�TXNZ`aR�[OU�P��(R�TXRadFR�T�giYxTI`aR�Mú]FP�Nb[_súP�|O[DUXm_R�UXNQv��(Y\TXÎDfbY{VxM_P´Nb[¥Y\TWMDR�T�UXY

TIR�d_fZNev�V*UXR&d_TXR��DNbY\]FP��(YxTIÎüV*[FM§V*fbfZY��ávwYx`adFV*TXNQPSY\[���NZUXm�TIR�V�fZÏi�(YxTIfQMÛ�(YxTIÎOfZY{VxM_Pw�ã�(m_RúPS|D[OUIm_R�UINQvTIRcno]_RcP�U�P�UITXR�V*`ÕPyvwYx[FP�NeP�UXR�M&Y*g D#��ë¼V\v�v�R�PIPSR�P } V�U�|Od_Nev�V*f�jFfZRäP�|KP�UXR�`ø^_fbYOv�Î)PSNZÙ�R\�B]_[_NkgiY\TX`afZ|#MONQP�ÏUITXNZ^_]KUIR�M�V\vwTXY{PXP�UImKRtV��xV*NbfQV*^KfZR�fZY\sxNQv�V�fªP�dFVxvwR{�2�(m_R�TIR�n{]_R�PSU2NZ[OUIR�TWV*TITXNZ�xV*fKUINZ`pR�PÖ�(R�TIR�R�ÔOdFY\[_R�[OUINeV*fbfZ|MDNeP�UITXNZ^_]KUIR�M���NZUXm¥UIm_Rp`aR�V*[ú�xV*TXNZR�M"UXY&sxR�[_R�TWV*UIRpfZNZsxmDUXR�T�V*[FMúm_R�V��DNbR�T��(YxTIÎOfZY{VxM_Pw�à�(m_RaT�V�UINbY�Y*gTIRcV\M_P(UXY���TINZUXR�P���V\PBP�R�U�UXY�5D� � �2�2V\v�m#M_V*UWVrdFY\NZ[OU�NQP2UIm_R�Vc�{R�T�V*sxRtY*glV*U�fbR�V\PSU(UXm_TIR�R�P�R�dFV�T�V�UIR�TI]_[ÐPY*g%5 �B> � >T>B> MDNeP�ÎaTXR�n{]_R�P�UWPw�KvwY\TXTIR�PSd5Yx[FMDNb[_s UXYaPSNZ`�]_fQV�UIR�M��(YxTIÎOfZY�V\M_P�Y*g �B> �H8 >T> m_Y\]_TWP;Y�gBV\v�UINZ�ONZUS|{�

7 >

Page 44: Aggressive Centralized and Distributed Scheduling ofDisk Requests

7 �

# ¡�©cR�¦ ` P ] £ _ 3F4 � Ä _�] ¡ O P + PSÄ�¡�à �¬`QÈ 3�R b��{R�[&Nkg�VpPIv�m_R�MD]_fbR�T�mFV\PyfbNZUXUIfZR�Y\Tt[KYaÎD[KY*��fbR�MDsxR�Y*gBUIm_R���ë���ÏØUXY\Ͼz�ë��ó`#V*dKd_NZ[_s�giY\T�V sxNZ�{R�[

MDNeP�Ϊ�DNZU�v�V*[ÕV*d_d_TXY�ÔDNb`#V*UXRtPSR�R�ÎpMDR�fQV�|KP�]FPSNZ[_s�UXm_R:WMDNQPSU�V*[ÐvwR�<r^FR�US�(R�R�[ fbY\s\Nev�V*fª^_fZYOv�Î�[D]_`�^FR�T�PÖgiYxTNZ[ÐMDNZ�ONQMD]ÐV*fTXR�no]KR�P�UWPw�aæ_YxT�R�Ô_V�`ad_fZR���V*[8��ë��yÏi^FV\PSR�M ~ Ͼ�ÖÞ�Þ��áPIv�m_R�MO]_fZR�T���NZfZflP�R�fbR�vwU�V#d5R�[FMDNZ[KsTIRcno]_RcP�UgiY\T���ë���5 >B> Y��{R�T2Yx[_R;giYxT���ë��Z7 >T> Någ�UXm_R�fQV\PSU2TIR�n{]_R�PSU�UXY�vwYx`ad_fbR�UIR�V\v�vwRcPIP�RcM ��ë�� �?>T> ��(m_R8V\v�v�]_T�Vxvw|ßY�g�UImKNQPaV�d_d_TIY�ÔONZ`#V�UINbY\[§MDR�dFR�[ÐM_PaY\[§UIm_Rúv�m_Y\NevwR�Y*g´PIv�m_R�MD]KfZNZ[Ks¥V�fZs\YxTINbUIm_`���UXm_R�xV*TXNQV*[ÐvwR�NZ[)P�R�v�UIY\TWP;dFR�T�UITWV\v�Îa^FR�US�(R�R�[aÙ�Y\[KR�Pw�_UXm_R�MDR�giR�vwU�PSfZNbd_d_NZ[KsDÝ�TXR�V*fbfZYOv�V�UINbY\[)PIv�m_R�`aR } P��W�OV*[FMV*[O|#v�Vxv�mKR�dKTIRwgiR�UWv�mKNZ[_säV\vwUXNZ�ONZUS|{�

æÖNZsx]_TIR � � � Vtd_TXR�P�R�[OU�PUXm_Ry`pR�V*[�TXR�P�dFY\[ÐP�R�UINZ`pR�PqgiY\TBæ ~ æ��F�{�ÖÞ�Þ���� ~ Ï°�ÖÞ�Þ����oý�� ~ Lt� } > �65{�X�V*[ÐMü�K�O��æÁgiY\TäV&T�V�[_s\RaY�gt`pR�V*[8V*TXTINZ�xV�f(T�V�UIR�P���æ ~ æ���n{]_Nev�ÎOfZ|àPIV*UX]_T�V�UIR�P�VxPrUIm_Rp�(Y\TXÎDfbY{VxM"NZ[_ÏvwTXR�V\PSR�Pw���{NZ[ÐvwR ~ Ï°�ÖÞ�Þ�� TIR�MO]FvwR�P(UXm_RrTXR�P�dFY\[ÐP�RrUXNZ`aR��xV*TXNQV*[ÐvwR } V\P��(R�fbf�V\P�UImKRr`aR�V�[h���ONZUWP(`aR�V*[TIRcP�dFY\[FPSRtUINb`aR�TI]K[FP � � �?>H� m_Nbs\m_R�T2UXmFV*[aUXm_Y{PSRtY*g��ÖÞ�Þ����Dýr� ~ Lt� } > �65{�I�OV�[FM&�_�O��æ&giY\T(`pR�MDNZ]K`V*[ÐM&m_R�V��D|p�(Y\TXÎDfbY{VxM_Pw���(m_R �x�X� vwY\[OjªMDR�[Fv�RrNZ[OUIR�TI�xV*feP�P�m_Y���[�NZ[ajFsx]_TIR � � � ^�P�]Kd_dFY\TIU�UXm_R�P�R�Yx^_ÏP�R�TI�xV*UXNZY\[ÐPw�B×yY��(R��{R�T��{UIm_R�NZ[OUIR�TI�xV*feP�giY\T��ÖÞ�Þ�� } ��m_Nev�m#V�TIR�U�|Od_Nev�V*fFgiY\T�ýr� ~ L�� } > �65o�BV�[FM��K�O��æV\P(�BR�fZfi��`#V�Î{R�NZU�MONåÒÕvw]_fZU�UIY�d_TXR�MDNQv�U�UXm_R�TIR�feV*UINb�{R�dFY{P�NbUINbY\[FP(Y�g��ÖÞ�Þ����Dý�� ~ Lt� } > �65{�X�_V*[ÐMà�K�O��ægiY\T�Vrs\Nb�{R�[)V*TXTINZ�xV�f�T�V*UXR{�

æÖNZsx]_TIR � � � v#P�m_Y���PrUImKR#PIn{]FV*TXR�MÛvwY{RwÒÕvwNZR�[DUWP�Y�g��xV*TINeV*UXNZY\[ }�� -����&-c��giY\T�UXm_R#PIV�`aRpP�R�U�Y�g�R�ÔDÏdFR�TINb`aR�[OU�P��tæ ~ æ��#mFV\PtUXm_R�fZY��(RcP�U�vwY{R�Ò#vwNbR�[OU;giYxTtUIm_R�fbNZsxmDUXR�P�Ut�BY\TXÎDfbY{V\MKPw��LtP�æ ~ æ��#^FR�sxNZ[FPtUXYPIV�UI]_TWV*UXR{� ~ Ͼ�ÖÞ�Þ�� R�`pR�TIsxR�P(VxPyUIm_RäV*fbs\Y\TXNZUXm_`á��NZUIm)UIm_R�^FR�PSU�P�UWV*TI�xV�UINZYx[�TIR�PSNQPSU�V*[ÐvwR{�y�_�o��æ(�5Yx[UImKRÓYxUIm_R�T�mFV*[FMª��NePrm_NZsxm_fZ|8P�]FPXvwR�d_UXNZ^_fbRaUIY8P�UWV*TX�\V�UINbY\[��ÛL�U�V�[�V*TXTINb�\V�f(TWV*UIR#Y�g �B> TXR�no]KR�P�UWPrd5R�TP�RcvwY\[FMª�_UIm_R�vwY{RwÒÕvwNbR�[DUBY*g��xV*TINeV*UXNZY\[#giY\Tt�_�o��æòNQP^C�8 � sxTIR�V�UIR�T�UImÐV*[&UXmFV*U�Y�g ~ Ͼ�ÖÞ�Þ����# ¡�©cR�¦ ` P ] £ _ Æ ] ¤�© O¢� £cÄXÆ�£ ! O ÁQÁ ] £ _

ÜØg�VpPIv�m_R�MD]_fbR�T�mFV\PyÎO[_Y���fZRcMDs\R�Y�g���ë���ÏØUXY\Ͼz�ë�� `ÕV*d_d_Nb[_s{P��5NbU�v�V�[�`aY\TXR�V\v�vw]_T�V�UIR�fb|#d_TIR�MONQvwUP�R�R�΢MDR�fQV�|KP�V*[FMßUXm_R�TXR�^D|Ûd_TXYOMD]FvwR�^FR�UXUIR�TpPIv�m_R�MO]_fZR�P���æ_Y\TaUXm_RÓgiYxfZfbY*��Nb[_s8P�R�U�Y*g�R�ÔOdFR�TINb`aR�[OU�Pw�UImKR�PIv�m_R�MO]_fZNb[_s�V*fbs\Y\TXNZUXm_`#P(mFV��{Rtgi]_fZf�`ÕV*d_d_Nb[_s{P(giY\T�R�Vxv�màvw|DfbNZ[FMOR�T�V�[FM�V´mKR�]_TINeP�UXNQvygiY\T�v�mKY{Y{P�Nb[_s^FR�US�(R�R�[a` ]KfZUINbd_fZR�dFR�[ÐMDNZ[_s�TIRcno]_RcP�U�P(UXY�UIm_R�PXV*`aR�vw|OfZNb[FMDR�T } PSR�R�P�R�v�UINZYx[�8_�67O� � ���

æÖNZsx]_TIR � �U5¥MDNQPSd_fQV�|KP UImKR&`aR�V�[ßTXR�P�dFY\[ÐP�R�UINb`aR�P�V�[FM�PIn{]FV*TXR�M�vwY{RwÒÕvwNbR�[DUWP´Y�g��\V�TINeV*UINbY\[ßgiYxTUImKRa��ë��yÏi^FVxP�R�MúV*fbs\Y\TXNZUXm_`#PtV�[FM�UXm_RpV*fZsxY\TXNZUImK`#Py]_UXNZfZNbÙ�NZ[KsaV gi]_fbf2��ë��yÏiUIY\Ͼz2ë�� `ÕV*d_d_Nb[_s_�ä�(m_R��ë��yÏi^FV\PSR�M¥V�[FM�gi]_fbfZÏi`#V*d��{R�TWP�NbY\[FPtY*g�RcV\v�m¥V�fZs\YxTINbUIm_`Ñd_TIYOMO]FvwR#V�fZ`aY�P�UtNeMDR�[OUINQv�V*fdFR�TSgiY\TI`ÕV*[FvwR} VxP�`aRcV\P�]KTIR�M�^D|�R�NZUImKR�T2`aR�UITXNQv*�W�Ö�{Nb[FvwR��(Y\TXÎDfbY{VxM_P(��NZUXm ]_[KNågiY\TX`afZ|äMDNQPSUITXNZ^_]_UXR�M�TIR�n{]_R�PSU(PSU�V�TIUINb[_sfZYOv�V*UINbY\[FP�vwY\[OU�V�NZ[&giR��óPSR�n{]_R�[OUINQV�fÖTXR�n{]_R�P�UWPw�Fd_TIR�giR�U�v�m_NZ[Ks d_TXY��DNeMDR�P�fZNZUXUIfbR�YxTt[_YadFR�TSgiY\TX`#V*[Fv�RrNZ`pÏd_TXY*�{R�`aR�[OU����(m_R�vw|OfZNb[FMDR�T�m_R�]KTINQPSUINev�V*fQPSY#mFV\P�Va`aNZ[KNZ`#V�f�RwéªR�vwU��±V\PtNZ[FMONZ�ONQMD]FV�fv�|DfbNZ[FMDR�T�PyTWV*TIR�fZ|vwYx[DUWV*NZ[8` ]_fbUINbd_fZR�dFR�[FMDNb[_s�TIRcno]_RcP�U�P��#�(m_RaYx[_fZ|ú�DNeP�Nb^_fZR�MDR��DNeV*UINbY\[¥^FR�US�BR�R�[8V*fZsxY\TXNZUImK`0�{R�T�PSNZY\[ÐPNQP�VúP�fZNbs\mOU Nb[FvwTXR�V\PSRÓNb[��_�O��æ(ç P vwY{R�Ò#vwNbR�[OU�Y*g��xV*TXNQV�UINZYx[ògiYxTaUIm_Ragi]_fbfZÏi`#V*d¢V�fZs\YxTINbUIm_`��¢�(m_NeP´NePTIRcV\P�Yx[FV*^KfZR{�2VxP´�_�O��æ§]_UINbfZNZÙ�R�Py`#V�d_d_NZ[Ks&ÎO[_Y���fZR�MDsxRaPSUITXNQvwUXfZ|&UXY�TIR�MO]FvwR�TIR�PSd5Yx[FP�RpUINZ`pR�P } V�UrUXm_RR�ÔOdFR�[FP�R�Y�gNb[FvwTIRcV\P�RcMÕTXR�n{]_R�P�U�PSU�V�TI�xV*UXNZY\[ª���

�qYpMDR�UXR�TI`pNZ[_R�UXm_R�NZ[�ªF]KR�[FvwRtY�g2R�ÔKvwR�PXP�NZ�{R�MDRwgiRcvwU�P2Y\[�PXv�mKR�MD]_fbR�T�Vxv�vw]_TWV\vw|{�OUIm_R�PSNZ`�]_fQV�UIY\TB��VxPTIRcvwY\[DjÐs\]_TXR�M&UIY�`aYOMDR�f�V*[ú×�z ~ 5B5�8 A ��NZUIm)mFV*fkgBY*g2NbU�PtPSdFV*TXRrUITWV\v�Î_P } 8 �T> Y\]KUtY*g �B>T> ��YOv�vw]_d_NbR�MMD]_RBUIYtTWV*[FMOY\`afb|�sxTIY���[�MDRwgiRcvwU�P��Ö��Yt`#V�ÔDNb`aNZÙ�RÖUXm_R(dFR�TXUI]_TX^FV*UXNZY\[�Nb[�UIm_R���ë��yÏiUIY\Ͼz2ë��ò`#V�d_d_Nb[_s_�V*fbfFY*g�UXm_R�MDRwgiR�vwUWPÖTIRcP�]_fbUIR�MrgiTIYx`�MD|D[ÐV*`aNev�TIRcV*fZfbYOv�V*UXNZYx[ } N°� R��Z��[_Y�PSfZNZdKd5RcMrUIT�Vxv�ÎKP��W�2��{R�[���NZUXm Y��{R�T5 � Y*g�VúMDNQPSÎhç P�UXT�V\v�ÎKPrTIR�`#V�d_dFR�Mh�Ögi]_fbf�`#V*dKd_NZ[_s)NZ[DgiYxTI`#V�UINbY\[¥d_TXY��DNeMDR�PrfZNbUIUXfZRaNb`ad_TIY��{R�`�R�[DUtNb[dFR�T�giYxTI`#V�[FvwR{�a�_�o��æ(��UIm_RpV*fbs\Y\TXNZUXm_`0`aY{PSU�P�R�[FP�NbUINZ�{R�UIY)UIm_Rp��ë��yÏiUIY\Ͼz2ë�� `ÕV*d_d_Nb[_s_�ªNZ`ad_TXY��{R�P

Page 45: Aggressive Centralized and Distributed Scheduling ofDisk Requests

7B5

� � FCFS� � C-LOOK� � LOOK� � VSCAN(0.2)� � SSTF

|�0� |�

10� |�

20� |�

30� |�

40� |�

50� |�

60� |�

70�|�0

|�50

|�100

|�150

|�200

|�250

Mean Arrival Rate (Hz)

Mea

n Re

spon

se T

ime (

ms)

! ! ! ! !!

!

" " " " ""

"

# # # # ##

#

$ $ $ $ $$

$

²´ºjß&%¢¹�º,Â('7¹�¼�Ø"Ç2Â"¼�¹*)�ÄÈÌ�¹

|�0� |�

10� |�

20� |�

30� |�

40� |�

50� |�

60� |�

70�|�0

|�50

|�100

|�150

|�200

|�250

Mean Arrival Rate (Hz)

Mea

n Re

spon

se T

ime (

ms) FCFS+ C-LOOK, LOOK,

².-sß&/2³Ê¶10�Ç2Â32Ù»j¹Â"É�¹*4(ÂjÃ9¹·9Ï�º�Æм ²�%¢¹�º,Â5'7¹�¼�ØgÇ2Â"¼�¹6)�ÄÈÌ�¹,ß

7 7 FCFS8 8 C-LOOK9 9 LOOK: : VSCAN(0.2); ; SSTF

|�0� |�

10� |�

20� |�

30� |�

40� |�

50� |�

60� |�

70�|�0.00

|�0.25

|�0.50

|�0.75

|�1.00

|�1.25

Mean Arrival Rate (Hz)

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

< << <

< <

==

== = = =

> >>

> > > >

? ??

? ? ? ?

@@

@@

@ @ @

²�É�ßBA�À2Á"º£·9¹�»C0�Çj¹ED É5ÄȹÂjÃuÇ,ÞGF�º,·�Äź,Ã�ÄÈÇ2Â

(^]w_�`cb RIH&%�'*)���ë��yÏ°ë�VxP�R�M�L�fZs\YxTINbUIm_`ãzÖR�TSgiY\TX`#V*[Fv�R(]FPSNZ[_s�Vr�{|O[OUIm_R�UXNQv2�"YxTIÎOfZY{VxMr��NZUXma�y[KNZÏgiY\TI`pfZ| u NQPSUITINb^_]_UXR�M � R�no]KR�P�Ut�{UWV*TXUINZ[Ksa�hYOv�V�UINbY\[FP

Page 46: Aggressive Centralized and Distributed Scheduling ofDisk Requests

7B7

J J FCFSK K LOOK (LBN)L L C-LOOK (LBN)M M SSTF (LBN)N N VSCAN(0.2) (LBN)O O LOOK (MAP)P P C-LOOK (MAP)Q Q SSTF (MAP)R R VSCAN(0.2) (MAP)

|S0T |S

10T |S

20T |S

30T |S

40T |S

50T |S

60T |S

70T|U0

|U50

|U100

|U150

|U200

|U250

Mean Arrival Rate (Hz)

Mea

n R

espo

nse

Tim

e (m

s)

V V VV

V

V

W W WW

WW

W

X X XX

X

X

X

Y Y YY

YY

Y

Z Z ZZ

ZZ

Z

W W WW

WW

W

X X XX

X

X

X

Y Y YY

YY

Y

Z Z ZZ

ZZ

Z

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

r r FCFSs s LOOK (LBN)t t C-LOOK (LBN)u u SSTF (LBN)v v VSCAN(0.2) (LBN)w w LOOK (MAP)x x C-LOOK (MAP)y y SSTF (MAP)z z VSCAN(0.2) (MAP)

|S0T |S

10T |S

20T |S

30T |S

40T |S

50T |S

60T |S

70T|U0.00

|U0.25

|U0.50

|U0.75

|U1.00|U1.25

Mean Arrival Rate (Hz)

Squ

ared

Coe

ffic

ient

of V

aria

tion

{{

{{

{{

||

|

|| | |

}}

}} } } }

~~

~

~~

~ ~

��

�� � �

||

|

|| | |

}}

}} } } }

~~

~

~~

~ ~

��

�� � �

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

������`����I��� ��¡£¢ �¥¤q¤q¦�_�\§e¨\�bj�5©Gª�«¬¦�ª�\3dk`­�¯®°¤q±3gi�En��E²³pµ´�`��k�.gi�Ep¶\�bj��`��jdfnqb³±£\*��·¸b��E²¥`��En¹�»º¼g3�¾½¸¦¤qg�\i�À¿�n��E²ÂÁ¬b³nÃ�.g3�EpĤq·(Ŭn¹dk�E�¾nq�³�¥�E`��À�Æ��\§�¾�En�b³±C©�g��Ç\§�En�g3bjd

Page 47: Aggressive Centralized and Distributed Scheduling ofDisk Requests

餃

��·Ê¤�`�dEdB�E²j\�bÌË�ÍCÎBlo²��jd�Ïjdk`�`�½�¦.�E`��¸�Ð��nqb³±¨\�¤q±3gi�En��E²³p¶dBg3�³�Ñ\§n�bÀgib³¤q·Ä\Òp¶\��E±3n�bj\§¤j�j`�b³`�Ój�o�.�EgipÔ\i����`�d¾d�Eg��.�³¤�¤³©Gª�«¬¦.�Egi¦�´Bª�«Õp¶\�e³e³nqb¥±�dG¿�²³`�b5d¾��²¥`��¸�³¤�nqb³±°¿ogi�E½�¤qg�\i�³dG¿�nq�E²¨�³b³nÃ�.g3�EpĤq·£�¸n�df�E�En��³�³�¾`��¯�¾`��^�¥`�dk�dk�Ñ\§�¾�Enqb¥±Ê¤�g���\§�¾nqg3bÐd�Î

ÖØקÙ���ÚQ`�Û��.Ü��IÝ(��Þ�Ùß��`�Û�Û�àÂÜâá�Ý(Û���Ú��h�ã nqä�`�bådk�¸����nq`Çb¸�°��gipCe³�³�Ñ\§�¾nqg3bÂ�E`�dfg3�³�Ñ��`�d�Ï�\æ�.�¥¤q¤&©Gª�«¬¦��¾g3¦�´Bª�«çp¶\�e³e³nqb¥±³Ï�\3�����¥��\§�¾`5pC`���²j\§b¥¦

n��Ç\§¤�\§bj�Õg�ä�`��¾²³`�\3�¼dkej`���nèÓ���\��En�g3bjd�ÏB\§bj�édkgipC`(nqbj�¸n¹��\§�¾nqgibÌg��°�E²³`¶���³�E�¾`�b¸�6�¾g3��\��En�g3bj\�¤�ehgÆdkn��Enqgibég§��E²¥`C\i���E�j\��Egi��ÏB\ad¾��²¥`��¸�³¤�`��¨��\§bêdk`�¤�`����6�E²¥`Êej`�bj��nqb³±Â�E`����³`�df�¯�¾²j\§�¨¿�nq¤�¤ën�bj���³�6�¾²³`Cdfp¶\§¤�¤q`�df�*�Egi��\�¤ejg�dfnq�En�g3b³n�b³±Ò�¾nqpC`6[.n�Î�`�ÎqÏidk`�`ǽ(\§bj�C�Egi��\��Enqgibj\§¤�¤�\��E`�bj��·h]G�.g3��\6±3nqä�`ÇbC�¸n¹dk½�Î�®*dB¿�nq�¾²À�³�^l ¢ ϸ�¾²³`¬�Ð\3dkn¹���´Bl ¢ \�¤q±ig3�En��E²³pìn�do²³n�±3²³¤�·¶dk�jd¾��`�e³�¾nq�³¤�`*�Eg5�¾`����³`�dk�°df��\��Eäi\§�¾nqg3bØÎ

¢ nq±i�³�E`í¸Î È e³�¾`�dk`Çb¸�Ñdîej`��f�.g3�Ep�\§bj��`��³\���\¬�.g3� ¢ � ¢ �jÏ3�B¦�©âï¯ï£ð5ϸ�³�^l ¢ Ï^�^´ël ¢ Ï3\�bj�5®¯��´Bl ¢ [.ºñ][�\�b�\�±3`�¦�dk`�bÐdknq�¾nqä�`6ä�`��Ñdknqgib¶g§����´Bl ¢ �¸`�dE���Enq�j`��Cn�badf`����¾nqg3b É Î È Îóò^]ÑÎ�®*doº n�bj���E`­\3dk`­dë�.�Eg3pôò5�Eg È3õ Ï�E²¥`apC`�\�bö�¾`�dkejg3bÐdk`��En�pC`Cg��5®6��´Bl ¢ dk¤qg�¿�¤�·÷±i�Eg�¿°d�Ï�¿�²³n�¤q`Ânq��d5�E`­dkejg3bjdf`��En�pC`¶ä3\��En¹\§bj��`å�¸�Egiejddkn�±3b³nÃÓ���\�b¸�¾¤q·�Îølo²³`Õ��´Bl ¢ \§bj�ù®¯��´Bl ¢ \§¤q±ig3�¾nq�E²¥p¶dæ²Ð\­ä�`¼��g3bjdfn�dk�¾`�b��E¤q·é¤�g§¿�`��CpC`­\§bö�¾`�dkejgibjdk`�En�pC`�d��E²Ð\§b¶�E²³`údk`�`�½�¦.�E`��¸�Ð��nqb³±m\§¤�±3g3�¾nq�¾²³p¶dëgi� ¢ � ¢ �jÎ ¢ g3��²³nq±i²³`���äi\§¤��³`�dog���ºµÏj®¯��´Bl ¢ dk��û�`Ç��d°\dk²Ð\§�Ee(nqbÐ���E`�\idk`�n�bÊpC`­\§bÒ�¾`�dkejgibjdk`*�¾nqpC`�\ido\6�¸n�df½Ò�j`�±inqbjd��Eg¨d¾\§�E�¥��\§�¾`�Î ¢ g3��\6dk�¸����n�`�b¸�¾¤q·6¤�\��E±i`�ºµÏ®¯��´Bl ¢ �¸`�±i`�b³`��Ñ\§�¾`�donqb��Eg ¢ � ¢ �jÎ

_ag��¸nè�.·�nqb¥±Ê��´Bl ¢ ¿�nq�E²�\§b¶\�e³e³�Egie³�En¹\§�¾`6\§±inqb³±6��\3���¾g3�o�¾`�dk�¥¤q��dBnqbÄ\§b¶\�¤q±ig3�En��E²³pü¿�n��E²C�¾²³`°pC`�\§b�E`­dkejg3bjdf`5�En�pC`*g§�°��´Bl ¢ \§bj�a�¾²³`5df��\§�¾äi\§�En�g3b¼�E`�dfn�df��\§bÐ��`6g§�°�B¦�©âï6ï£ð5Î ¢ gi�*`�ý¥\§pCe³¤�`�ϳ®6��´Bl ¢ [�þ�]\§bÐ�Õ®¯��´Bl ¢ [¾Ë�ò^]°e³�¾g�ä¸n¹�¸`5`����³nqäi\§¤�`�b��*pC`�\�b��E`�dfehgibjdk`(�En�pC`�d¬�¾g���´Bl ¢ �.gi�5\§¤�¤��³�³�6�¾²³`ʲ¥`�\�ä¸n�`�dk�¿ogi�E½�¤qgÆ\3�³d�Ïÿ·�`Ç�ʲj\�ä�`ÂpÊ�j��²Õ�j`��¾�E`��¶df��\��Eäi\§�¾nqg3bß�¾`�dkn¹dk�Ñ\§bj��`ÆÎ���bö��\3���ÇÏ�®¯��´Bl ¢ [¾Ë�ò�]ʲÐ\3dC\̤�g�¿o`���E`­dkejg3bjdf`��En�pC`Cäi\§�¾n�\§bÐ��`��E²j\�bñ�B¦�©âï6ï£ð5Ï�`�ä�`�bé�E²³gi�³±3²ùnq�ÑdÊ��g�`��¶��nq`�b��5g§�6äi\��En�\��En�g3bßn�d(dk¤�nq±i²¸�¾¤q·²³n�±3²³`��ÇÎ

��`�¤�`����En�b³±Ò�¾²³`Ò�¾`����³`�dk��¿�n��E²¶�E²¥`Òdfp¶\§¤�¤q`�df�oejg�dfnq�¾nqg3b¥nqb³±Ä�¸`�¤¹\­·Ä`�b¸�Ñ\§n�¤�d�dkn�±3b³nÃÓ���\�b¸�°��gipCe³�³�Ñ\§�¾nqg3b[�`­dkej`���n¹\§¤q¤�·Ì�.g3�¶¤¹\§�E±i`¼�^�¥`��³`�d�]�Ï����¾Î�����\i��g���Ë��εÁ¬b¥¤q`�d¾dæ�¾²³`�ej`�bj�¸n�b³±é���³`��³`¼dfn��`Ân�d5�hgi�³bj�¸`­��Ϭn��p¶\�·a�j`C�¥bj\3����`�e³��\��³¤q`Ä�Eg�dfnqpCe¥¤q·���g3pCe³�¥�E`(\§bÐ�÷��g3pCej\��E`5�¾²³`Cejg�dfnq�En�g3b³n�b³±��En�pC`�dÿ�.gi�5\�¤q¤Bg§�°�¾²³`ej`�bj�¸n�b³±¶�E`����³`�df��d�ÎÊï°b³`C\��E`�\Ê�.gi�ú�.�¥�E�³�¾`5�E`�df`�\§�Ñ��²�n¹dú�¾²³`(�¸`�dfnq±ibÕ\�bj�In�pCe³¤�`�pC`�b¸�Ñ\§�En�g3b¶g§�ÿ��¤q`Çä�`���³\���\�dk�¾�E�j���E�³�¾`�dÒ�Eg�gi�E±�\�b³n�Ç`Cej`�bj�¸n�b³±¼�^�¥`��³`�d6nqbédf�j��² \¶p¶\§b³b¥`��5\idÒ�Eg¼dk�¾�E`�\�pC¤qn�b³`5�E²¥`¶dk`�\�����²�.g3�£�E²³` ����¤�g�dk`­dk���Cej`�bj��nqb³±C�¾`����³`�dk�ÇÎ*lo²³`(\i�³�¸n��Enqgibag���\�bÕ\�±3n�b³±Ê��\3���Eg3�°�.�³�E�¾²³`��6��gipCe³¤�n���\��E`�dB�E²³n¹de³�¾g3�³¤�`�p�Î

��������� ���������! #"%$� &�('!)+*�,.-/ &�lo²³n�d�dk`����EnqgibC��g3b���\§n�bjdë`Çý¸ej`��¾nqpC`�b���dG��g3pCej\��En�b³±6²³g�df�E¦.�j\3df`��¶dE��²³`��¸�³¤�`���dâ�.gi�o�E²¥`10*´ê\§bj�CÅ�2�

�E�Ñ\3��`­d�ÎÂlo²³`Cej`��k�.gi�Ep¶\�bj��`5±i��\§e¥²jdÒnqbÕ�¾²³n�d6df`����En�g3bÕ�Ðdk`Ä\a��\§b¥±3`Cg��°�E��\i��`ÄdE��\�¤qnqb¥±À��\3���Eg3�Ñd�Ϋ¬g3�¾`�E²Ð\§�*�¾²³`(dE��\�¤qn�b³±Ê��\3���Eg3�m[��E²¥`43*¦�\�ý¸n¹d�]�n�d*df²³g�¿�b�nqb�¤�g3±�56d¾��\§¤�`�Î6lo²³`Ò¿�g3�¾½¸¤�g�\3�¥dú¿�n��E²¼\�b�n��¸`�b��En��f·dE�Ç\§¤qn�b³±¬��\i���Egi�B��g3�¾�E`�dfejg3bj�Ê�¾g*�E²¥`��E��\i��`��Ò�¾`��^�¥`�dk�&dk�¾�E`�\�p¶d�Î&lo²³`�nqb³n��En¹\§¤�`�ý¸ej`��¾nqpC`Çb¸�Ñd���gipCej\§�¾`o�¾²³`ej`��k�.gi�Ep¶\�bj��`�g����¾²³`°�j\3df`�¤qn�b³`°dE��²³`��¸�¥¤qnqb¥±6\§¤�±3g3�¾nq�¾²³p¶d�Î����¥�jdk`����³`�b���`�ý�ej`��En�pC`�b���dGdf�E�j�¸·(\�¤q±ig3�En��E²³pej`��k�.gi�Ep¶\�bj��`*¿�n��E²Âdk`­�^�³`Çb¸�¾n�\§¤ØdE��²³`��¸�¥¤qnqb¥±Òg3e¥�EnqpÄn��\��Enqgibjdo\�bj� ¢ � ¢ �Ä��gipCp¶\§bÐ�¸¦����³`��¥`��Ê��n�dk½¥d�Î

ÖØקÙ���ÚQ`�Û��.Ü��7698!:oáj�j�.×�;³Û�<5Û.áG×>=@?¬`&AB6B�¸�¢ nq±i�³�E`­d5í¸Î É>C í�ÎD��e³�E`�df`�b��5�E²³`¶pC`�\�bÕ�E`­dkejg3bjdf`a�¾nqpC`�d6\�bj�÷�¾²³`Â��g3�¾�E`�dfehgibj�¸n�b³±Õd¾�^�Ð\§�E`­�ö��g�`��.¦

Ó���n�`�b���d¯g��*äi\��En�\��En�g3b÷�.gi�(©Gª�«¬¦.�j\3df`��öd¾��²³`­�¸�³¤qn�b³±ag��*�¾²³`Âdkn�ýE0*´ \�bj�éÅ12o�ü�E�Ñ\3��`­d�ÎE2�ý³��`�e³�Òn�b

Page 48: Aggressive Centralized and Distributed Scheduling ofDisk Requests

È í

F F FCFSG G C-LOOK (LBN)H H SSTF (LBN)I I ASPTF(30)J J ASPTF (12)K K ASPTF (6)L L ASPTF (2)M M SPTF

|N0O |N

10O |N

20O |N

30O |N

40O |N

50O |N

60O |N

70O|U0

|U50

|U100

|U150

|U200

|U250

Mean Arrival Rate (Hz)

Mea

n R

espo

nse

Tim

e (m

s)

P P P P

P

P

Q Q QQ

QQ

Q

R R RR

RR

R

S S S SSSS

S

T T T TT

TT

T

U U U UU

UUU

U

V V V VV

VVV

V

W W W WW

W

W

W

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

X X FCFSY Y C-LOOK (LBN)Z Z SSTF (LBN)[ [ ASPTF(30)\ \ ASPTF (12)] ] ASPTF (6)^ ^ ASPTF (2)_ _ SPTF

|N0O |N

10O |N

20O |N

30O |N

40O |N

50O |N

60O |N

70O|U0.00

|U0.25

|U0.50

|U0.75

|U1.00|U1.25

Mean Arrival Rate (Hz)

Squ

ared

Coe

ffic

ient

of V

aria

tion

``

``

``

aa

aa a a a

bb

bb

b b b

cc

cc c c c c

dd

dd

d d d d

ee

ee

e e e e e

ff

f

f

f f f f f

gg

g

g

gg g g

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

������`����I����hG¡£¢ �¥¤q¤q¦�ð*b³g�¿�¤q`���±3`6®¬¤�±3gi�Enq�¾²³p ´â`Ç�k�.g3�¾p¶\§bÐ��`¬�Ðdknqb¥±C\C��·�b¸�¾²³`��En¹�ÿº¼g3�¾½¸¤�g�\i�À¿�nq�¾²Á¬b³nè�.gi�EpC¤�·(Ŭn�df�E�¾nq�³�³�¾`��¶cÿ`­�^�³`­dk�¬�Æ��\§�¾�En�b³±C©�g��Ç\§�En�g3bjd

Page 49: Aggressive Centralized and Distributed Scheduling ofDisk Requests

È þ

i i FCFSj j C-LOOK k k LOOK l l VSCAN(0.2) m m SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

r r r rrrrr

s s s s s s

s

t t t t t t

t

u u u u u u

u

v v v v v v

v

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

w w FCFSx x C-LOOKy y LOOKz z VSCAN(0.2){ { SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0.0

|U2.5

|U5.0

|U7.5

|U10.0

|U12.5

|U15.0

|U17.5|U20.0

Trace Scaling Factorq

Squ

ared

Coe

ffic

ient

of V

aria

tion

| | || | | | |

} } } }}}

}

~ ~ ~ ~~~

~

� � � ���

� � � � ��

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

������`��§����� « ¡4����������� ©Gª�«¬¦�ª�\idk`��¶®¬¤�±3gi�Enq�¾²³p ´â`Ç�k�.g3�¾p¶\§bÐ��`

Page 50: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��

� � FCFS� � C-LOOK � � LOOK � � VSCAN(0.2) � � SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

� � � � ��

� � � � ���

� � � � ���

� � � � ���

� � � � ���

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

� � FCFS� � C-LOOK� � LOOK� � VSCAN(0.2)� � SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0.0

|U2.5

|U5.0

|U7.5

|U10.0

|U12.5

|U15.0

|U17.5|U20.0

Trace Scaling Factorq

Squ

ared

Coe

ffic

ient

of V

aria

tion

� � �

�� �

� � �

��

� � �

� � �

��

�� �

� � �

��

� � �

� � �

� � �

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

������`����I��� ��¡%�¡ �¢¤£���� ©Gª�«°¦�ª�\idk`��¶®¬¤�±3g3�¾nq�¾²³pÔ´�`��k�.gi�Ep¶\�bj��`

Page 51: Aggressive Centralized and Distributed Scheduling ofDisk Requests

È�¥

¦ ¦ FCFS§ § C-LOOK ¨ ¨ LOOK © © VSCAN(0.2) ª ª SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

« « « « ««

«

«

¬ ¬ ¬ ¬ ¬¬

¬

¬

­ ­ ­ ­­

­

­

® ® ® ®®

®

®

¯ ¯ ¯ ¯¯

¯

¯

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

° ° FCFS± ± C-LOOK² ² LOOK³ ³ VSCAN(0.2)´ ´ SSTF

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00|º128.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

¼ ¼¼

¼¼¼ ¼ ¼

½ ½½

½½

½ ½ ½

¾ ¾¾

¾¾

¾ ¾

¿ ¿¿

¿¿

¿¿

À À

À

ÀÀ

ÀÀ

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

�����9Á����I����ÂG¡%Ã�ÄÆÅ�ÇÉÈ�ÊÌËÍ� ©Gª�«¬¦�ª�\3df`��¶®¬¤q±ig3�En��E²³pì´â`��f�.g3�¾p¶\§bj��`

Page 52: Aggressive Centralized and Distributed Scheduling ofDisk Requests

È �

Î Î FCFSÏ Ï C-LOOK Ð Ð LOOK Ñ Ñ VSCAN(0.2) Ò Ò SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

Ó Ó Ó Ó Ó ÓÓÓ

Ó

Ô Ô Ô Ô Ô Ô ÔÔ Ô

Ô

Ô

Õ Õ Õ Õ Õ ÕÕÕÕ

Õ

Ö Ö Ö Ö Ö ÖÖÖÖ

Ö

× × × × × ××

×

×

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

Ø Ø FCFSÙ Ù C-LOOKÚ Ú LOOKÛ Û VSCAN(0.2)Ü Ü SSTF

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00

|º128.00

|º256.00|º512.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

Ý ÝÝÝÝÝ Ý Ý

Ý

Þ Þ ÞÞ

ÞÞÞ Þ Þ

Þ Þ

ß ß ßß

ßßßß ß ß

à à àà

àà

à à à

á á áá

áá

áá á

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

�����9Á��§�����ãâ�¡%�åäÌÄ�Çæç�9� ©Gª�«¬¦�ª�\idk`��¶®¬¤�±3gi�Enq�¾²³p ´â`Ç�k�.g3�¾p¶\§bÐ��`

Page 53: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É�õ

è è FCFSé é C-LOOK ê ê LOOK ë ë VSCAN(0.2) ì ì SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

í í í í

í

í

î î î î î îî

î

î

ï ï ïï

ïï

ï

ð ð ðð

ðð

ð

ñ ñ ññ

ñ

ñ

ñ

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

ò ò FCFSó ó C-LOOKô ô LOOKõ õ VSCAN(0.2)ö ö SSTF

|÷0.125ø |÷

0.250ù |÷0.500ú |÷

1.000û |÷2.000û |÷

4.000û|ü0.25

|ü0.50

|ü1.00

|ü2.00

|ü4.00

|ü8.00

|ü16.00

|ü32.00|ü64.00

Trace Scaling Factorý

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE!

þ

þþ

þ

þ þ

ÿÿ

ÿÿ ÿ ÿ ÿ ÿ

��

� � � �

��

� � � �

��

��

� �

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ���������G¡�� Å�� � Å � ©Gª�«¬¦�ª�\3dk`­�À®°¤q±3gi�En��E²³p ´�`��k�.gi�Ep¶\�bj��`

Page 54: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É Ë

FCFS C-LOOK � � LOOK � � VSCAN(0.2) SSTF

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

� � � � �

� � � � ��

��

� � � � ��

� � � � ��

� � � � ���

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

� � FCFS� � C-LOOK� � LOOK� � VSCAN(0.2)� � SSTF

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00

|º128.00

|º256.00|º512.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

�� �

��

�� � � � � � � �

�� � � � � � � �

�� � �

� � ��

�� � �

� �

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

�����9Á��§�������G¡%È�� � ��Å"! � ©Gª�«¬¦�ª�\idk`��¶®¬¤�±3gi�Enq�¾²³p ´â`Ç�k�.g3�¾p¶\§bÐ��`

Page 55: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É ò

lî�Ñ\3��` ����\�¤q` ¢ \3���¾g3� �B¦�©âï6ï£ð ©âï¯ï£ð �Ò�³��®£«Ò[ õ Î ò^] �³�^l ¢�B`�¤q¤�g ËiÎ í Ë È§É ËÇò�� Ë�ò � Ë�ò ¥��bj\�½�` ËiÎ ò3í � ËiÎ í ��È Î � ��È Î � ��È Î þ®°nq�E¦�c°dkä ò�Î í É3É Î ò í¸ËiÎ ò í¸ËiÎ ò í È ÎD�����nq¦�l¬� ò�Î í È ËiÎ õ í É Î � í3í�Î � í � Î íï°���¸`Ç� ËiÎ õ ò���Î þ í¸ËiÎ � í¸ËiÎqË í¸ËiÎ Ècÿ`Çehgi�E� ËiÎ õ í���Î É þ È Î ò þ É Î ¥ ¥3õ Î ò

[�\�]�_a`�\§bÂc�`�dkejgibjdk`mlonqpC`�d°[�p¶d�]��jdfnqb³±Ä\5´��E`��.`Ç����²³nqb³±(ï°b³¦�ªogÆ\§�Ñ�aÅ*\���\À��\i��²³`

lî�Ñ\3��` ����\�¤q` ¢ \3���¾g3� �B¦�©âï6ï£ð ©âï¯ï£ð �Ò�³��®£«Ò[ õ Î ò^] �³�^l ¢�B`�¤q¤�g ËiÎ ò3í Ë É í Ë È§É Ë È�É Ë È3È��bj\�½�` õ Î È§É þ3í�Î í þ3í�Î í þ3í�Î É þ3í�Î ò®°nq�E¦�c°dkä ò�Î õ É3É Î ¥ É�È ÎqË É ò�ÎD� É�È ÎqË����nq¦�l¬� ËiÎ þ�� �3ò�Î þ þ É Î É þ È Î þ þ¸ËiÎ ¥ï°���¸`Ç� õ Î þ � í � ÎqË í3ò�Î ¥ í3ò�Î ò í¸ËiÎ Écÿ`Çehgi�E� õ Î � Ë þ õ Î ò í3í�Î È í3í�Î í í É Î þ

[.��]�_a`�\§bÂc�`�dkejgibjdk`mlonqpC`�d°[�p¶d�]��jdfnqb³±Ä\Ê��ej`�`���¦�_�\�����²³nqb³±Cï°b³¦�ªog�\����ÂÅ*\§�Ñ\ʪo�¸û�`��

#�;�6�Û.�I���%$j¡ ��\�pCe³¤�`5_a`�\�b¼cÿ`�dfejg3bjdf`¶lonqpC`­d�.gi�Ò©Gª�«°¦�ª�\idk`���®¬¤�±3gi�Enq�¾²³p¶d'&)(+*-,/.10325476/89(;:<.= ,>0<.1.@?;A'6-2B(;:<.DC3.@*-0FEG.@? HI6/0J? .'KMLN8O.QP+R<4;ST.@?M256T4U(;:<.D?%LWVF(;4�*TP+.@?+X

�E²¥`6��\3df`6g§� ��������� Ï�\§¤�¤G\�¤q±3gi�En��E²³p¶dBej`��k�.gi�EpÔ`����j\�¤q¤q·Ò�.gi���E²³`6¤�g§¿�`�dk���E�Ñ\3��`6d¾��\§¤�nqb³±Ò��\i���Egi��d�df�E�j�¸n�`���΢ � ¢ �5ej`��k�.gi�Ep¶d�ejg�g3�¾¤q·5�.g3�°\�¤q¤j�³�³���E²³`*¤�nq±i²¸�¾`�dk�B¿ogi�E½�¤qgÆ\3�³d�ϳ\3dB¿�\ido�E�E�¥`ÿ�.gi���E²³`£dk·�b¸�¾²³`��¾n���¿og3�¾½¸¦¤qgÆ\3�³d�ÎBlo²³`*�¾`�¤�\��Enqä�`�ej`��k�.gi�Ep¶\�bj��`°g§�G�¾²³`*gi�E²³`���\�¤q±3gi�En��E²³p¶d�Ï�²³g�¿o`�ä�`��ÇÏ��¸nÃû�`Ç��dâ�.�Egip �¾²j\§�Bg3�Ðdk`��¾ä�`���.g3�(�E²¥`adf·¸b��E²¥`��En¹�Ê¿ogi�E½�¤qg�\i�³d�Î lo²³`¶�E`­dk�³¤���dÒnqbÐ�¸n���\��E`¶�E²Ð\§�(�E²³` 0*´ü��ò3ò É(�<Y dÊe³�E`��.`�����²³nqb¥±���\i��²³`e³¤¹\­·¥d�\5¤�\§�¾±3`6�Egi¤q`6nqbÂ�¸`Ç�E`��¾pCnqb³n�b³±¨\§¤�±3g3�¾nq�¾²³pÔ`�û�`����¾nqä�`�b¥`�dEd�Î

®ü�¸n�df½¶¿�nq�E²¼\�b�g3b³¦.�jg�\����Õ��\i��²¥`5dk`Ç�Eä�n���`�d��E`­\3�a�E`­�^�³`­dk��d��.g3�6��\i��²¥`��a�³\���\Cp(�j��²(��\3dk�¾`��*�¾²j\§b�E²¥g�dk`5�¾`����³nq�¾nqb³±(pC`��¸n¹\Ê\i����`�d¾d�Î ���B�¾`�\3�a�¾`��^�¥`�dk�Ñd*\§�¾�Enqä�`m\§�6\Ä�¸n�df½anqb¤qgi±3n��Ç\§¤q¤�·Â\3dE��`�bj�¸n�b³±Cg3�Ñ�¸`��ÇÏdkgipC`��.��\3���Enqgib�[�gi��\�¤q¤�]�g����E²³`6�¥\§��\¯�.gi�o`�\i��²Ädk`­�^�³`Çb¸�¾n�\§¤j�¾`��^�¥`�dk�Bp¶\�·5\�¤q�¾`�\3�¸·(�j`*nqb(�E²¥`*e³�E`��.`�����²³¦nqb¥±a�Ç\3��²³`Ê¿�²¥`�bÌ�¾²³`(�E`����³`�df�Ò\��E�¾nqä�`�d�ÎClo²³`��¾`��.g3�¾`�Ï�\§¤�±3g3�¾nq�¾²³p¶d¬�¾²j\§�¨e³�E`�df`��Eä�`(\�b¸·�`Çý¸n¹dk�En�b³±¶�E`�\i�dk`­�^�³`Çb¸�¾n�\§¤�nq�f·5\i��²¥nq`�ä�`£dk�³ej`��¾nqgi�¬ej`��f�.g3�Ep�\§bj��`��.g3�°¿ogi�E½�¤qgÆ\3�³d���gib¸�Ñ\§n�b³nqb³±(\5dfnq±ib³nèÓ��Ç\§b��o�.��\3���Enqgib¶g§�dk`­�^�³`Çb¸�¾n�\§¤�g3�°²³nq±i²³¤q·(¤qg��Ç\§¤G�E`­\3�À�¾`����³`�dk�Ñd�Î

lâ\��³¤q`úí¸ÎqËÇ\¯¤�n�dk�ÑdB\ÒdE\�pCe³¤�`�ehginqb��ë�.�¾g3p �E²³`+�E½�b³`�`>�6g§��`�\i��²(�E�Ñ\3��` Y dBdk`��Bg���pC`�\§b(�E`­dkejg3bjdf`*�En�pC`���³�¾ä�`�d�Îålo²³`¶©Gª�«¬¦.�j\3df`��ö�B¦�©âï6ï£ð \�¤q±ig3�En��E²³påÏâ¿�²³n¹��²é\�¤q¿\­·¥dÒd¾��²¥`��¸�³¤�`�d*�E`����³`�df��d¯n�bÕ¤qgi±3n¹��\§¤�¤q·\3d¾��`�bj��nqb³±¶g3�Ñ�¸`��ÇÏâe³�¾g§ä�n���`�d¬²³n�±3²³`��6ej`��f�.g3�Ep�\§bj��`5�¾²j\§bê©âï6ï£ðæÏG�Ò�¥��®*«Ò[ õ Î ò�]°\§bj�é�³��l ¢ �.g3�5\�¤q¤�E�Ñ\3��`­dÿ`�ý¥��`�e¥� ��������� Î*©âï6ï£ðü\§bj�¶�Ò�³��®*«¨[ õ Îóò^]B±i`�b³`��Ñ\§¤q¤�·Cg3�¥�Eej`��k�.gi�Ep �³��l ¢ Ï�\idÿ�¾²³`�·¶d¾��²³`­�¸�³¤q`\§¤�¤Gdf`��^�¥`�b¸�¾n�\�¤h�¾`����³`�dk�Ñdën�bC¤qgi±3n��Ç\§¤q¤�·C\idE��`Çbj�¸nqb¥±Òg3�Ñ�¸`��°�¸�¥�Enqb¥±5�E²³` �Ñ\3d¾��`�bj�¸n�b³±��5e³²j\idk`6g§���¾²³`¨dE��\�b��·¥��¤q`ÆÎ10¬g�¿o`Çä�`���Ï�©âï6ï*ð5Ï��¨�³��®*«Ò[ õ Î ò�]�Ï�\§bj�Õ�³��l ¢ \�¤q¤�`Çý¸²³n��³nq�£dkn�pCnq¤¹\§��ej`��f�.g3�Ep�\§bj��`¨¿�²³`�b��¾²³`

Page 56: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É�È

lG��\i��` ����\§¤�` ¢ \i���Egi� �B¦�©âï6ï*ð ©âï6ï£ð �Ò�³��®*«Ò[ õ Îóò^] �¥��l ¢�B`Ǥq¤qg Ë3Î õ Ë3Ë3Îóí Ë3Ë3Îóí ËiË3Îóí Ë3Ë3Îóí��bj\§½�` Ë3Îóò3í ò¸Ë3Î ¥ ò¸Ë3Îóþ ò�Ë3Îóþ ò¸Ë3Î �®¬n��E¦�c¬dfä ò¸Îóí Ë�í¸Î õ Ë È Î ¥ Ë È Î � Ë È Î �����n�¦�l¬� ò¸Îóí ò3þ¸Î � ò3í¸Î � òií¸Îóí ò3í¸Î Èï¬�Ñ�¸`�� Ë3Î õ Ë � Îóþ Ë É Î ¥ Ë É Î ¥ Ë É Î ¥c�`�ejg3�¾� Ë3Î õ Ë É Îóí Ë É Îóò Ë É Î�Ë Ë È Î �

#�;�6�Û������ ��¡ ï°b³¦.�jg�\§�Ñ��Å*\§�Ñ\���\i��²¥`Òc�`�\i� 0°nq�°´â`��Ñ��`�b���\�±3`�d��.g3�£©Gª�«¬¦�ª�\idk`��¶®¬¤�±3gi�Enq�¾²³p¶d

¤�\idk��g��Ø\*dk`����³`�b��En¹\§¤�df`��^�¥`�bj��`Bg§���¾`��^�¥`�dk�Ñdîn¹d�dE��²³`��¸�¥¤q`��¬Ój�Ñdk��Î�ºß²³`�b5�¾²³n�dGg������³�Ñd�Ï��E²¥`��¸n¹dk½¨dk`��¾ä¸n¹��`�d�E²¥`5�E`����³`�df��d¬n�b�¤qg3±in���\�¤q¤�·a��`�dE��`Çbj�¸nqb¥±Cg3�Ñ�¸`���Ï���gipCe³¤�`��E`�¤�·Êb¥`�±�\��Enqb¥±À�¾²³`5ej`��k�.gi�Ep¶\�bj��`m\3�¸äi\§b���\�±3`g§�»�E²³`6e³�¾`��.`�����²³n�b³±5��\i��²¥`�Î

¢ g3� ��������� Ïî�B¦�©âï6ï£ð e³�Eg��¸�Ð��`�d�\Ò²³n�±3²³`���pÄ`�\§b(�E`�dfejg3bjdf`Ò�En�pC`��E²Ð\§ba�¾²³`*gi�E²³`��°df`�`�½�¦��¾`��¸�j��nqb³±\§¤�±3gi�Enq�¾²³p¶d�Î�©G\§�¾±3`5�³�³�Ñdk�Ñdÿg��o¿��¾nq�¾`¯�¾`����³`�dk�Ñdÿ�¾gC\(dkn�b³±3¤�`5�¸n¹dk½Â�¸gipCnqbj\��E`*�¾²³` ��� ����� `�b¸ä�nq�¾g3b³pÄ`�b¸�� c��³`�p � È ��Î5lo²¥`3Z\[ ÊÌÅ Z Ê;� �>��� Z  ¡�"] Ê �¸n¹dk½¼dk`Ç�Eä�n���`�d°\§¤�pCg�df�*²j\�¤è��g��°�E²³`5�¾`����³`�dk�Ñd�ÏG¿�nq�¾²Ìp�\§ý�nqp5�³p���³`��³`�¤q`�b³±i�E²jd�\§e¥e³�EgÆ\3��²³nqb³±mË õ3õiõ \§���E²³`�n��¸`�b��En��f·6dE��\�¤qn�b³±ÿ��\i���Egi��Î � bm\3�³��nq�En�g3bGÏi�E²³n¹dî�¾��\3��`���gib¸�Ñ\§nqbÐd�E²¥`odfp¶\§¤�¤q`�df�h�.�Ñ\3���¾nqg3b6g���dk`����³`�b��En¹\§¤i�E`�\i�ú�¾`����³`�dk�Ñd�Ï��E²��jd��j`�b³`�ÓÐ�Enqb¥±¬�¾²³`B¤q`�\idk���.�Egipñ�E²¥`ëe¥�E`��.`��Ñ��²¥nqb³±��\i��²³`ÆÎal�\§�³¤�`Cí�Î òa¤�n�dk�Ñd*�E²³`Cgib³¦.�hgÆ\§�Ñ�ö��\i��²³`(²³n��Ò��\��E`�d*�.g3�¨`�\3��²Ìg��*�¾²³`ÄdE\§pÄe³¤q`(ejg3nqb���d6±3n�ä�`�bÌn�b��\��³¤q`£í¸Î�Ë�\�Î ¢ g3�\§¤�¤h¿�g3�¾½¸¤�g�\3�¥dë`�ý¥��`�e³� ��������� ϳ�E²¥`¯�B¦�©âï6ï*ðø\§¤�±3g3�¾nq�¾²³pü`�ý�²³nq�³n���dB\¯²¥nq±3²¥`��o²³n��B��\§�¾`nqb¨�E²³`�gib³¦.�hgÆ\§�Ñ�Ê�³\���\6��\i��²³`ÆÎâ«°g3�E`��E²j\��B\*dfp¶\§¤�¤�nqpCe³�¾g�ä�`�pÊ`�b���nqbm��\3��²³`�²³nq����\��E`��Ç\§b(dkn�±3b³nÃÓ���\�b¸�¾¤q·\­û�`����Òej`��k�.gi�Ep¶\�bj��`�Ï&�¸�³`C�¾ga�¾²³`C¤qgib³±apÄ`���²Ð\§b³n¹��\§¤B��`�¤�\�·¥dún�bj���³�¾�E`��¼¿�²³`�bé\i����`�d¾dknqb¥±a�E²¥`CpC`��¸n¹\[�ä�`Ç��dk�Ðd�\3����`­dEdkn�b³±(�E²³`m��\3��²³`3]ÑÎB® �¸`����E`�\idk`6nqbÂdk`Ç�Eä�n���`6�En�pC`��.g3�°`�ä�`�bÂ\Êdfnqb³±i¤q`6�E`­�^�³`­dk�£��\§bÂ�E`�df�³¤q�nqb¶¤�g§¿�`������³`��¥`¯�¾nqpC`­d&�.gi�¬b��³pC`Ç�Eg3�Ðdëej`�bj�¸n�b³±5�E`­�^�³`­dk��d�Î

®*�³�¸n��En�g3bj\�¤h`Çä¸n¹�¸`�bj��`�g����E²³`°�j`�b³`�ÓÐ��dëg��&dE��²³`��¸�¥¤qnqb¥±*�Eg¨`�ý¸e¥¤qg3n���\¯e³�¾`��.`�����²³n�b³±6��\i��²³`£\§�¾`ÿ�.gi�³bj���·¼��g3pCeÐ\§�En�b³±C�Ñ\§�³¤�`�d6í¸ÎqËÇ\a\�bj�Õí¸Î�Ë��GÎÄlo²³`(¤�\§�¾�E`��6�Ñ\§�³¤�`ʤ�n�dk�Ñd*dE\�pCe³¤�`5ehginqb���d*�.�Eg3p `Çý¸ej`��¾nqpC`�b���d¿�²³`��¾`B�E²³`�gib³¦.�hgÆ\§�Ñ� �Ñ��\3��²³`>���.�³bj���¾nqg3bÐdîgib³¤q·£\3d�\�dkej`�`���¦�p¶\�����²³nqb¥±o�³�¸û�`��ÇÎ�Á¬bÐ�¸`��G�E²¥n�dh�¾`�dk�¾�En¹���En�g3bGÏ�E²¥`*ej`��k�.gi�Ep¶\�bj��`*g��B�B¦�©âï6ï£ðü�¸�Egiejd��¸�Ñ\§p¶\��En��Ç\§¤q¤�·Òn�bÀ�¾`�¤�\��En�g3bC�¾g5�E²³`*gi�E²³`Ç��dk`Ç`�½¸¦.�E`­�¸�j��n�b³±5\�¤q±3gi¦�En��E²³p�d�Î ¢ gi�¬`Çý³\�pCe³¤q`ÆÏÐ�B¦�©âï6ï£ð d¾��²³`­�¸�³¤qn�b³±5g§�»�E²³` �åäÄ�ÇÌæç� �¾��\3��`¯�Ðdknqb¥±¶\m�.�¥¤q¤q·(�.�³bj���¾nqg3b¥nqb³±5gib³¦�jg�\����C��\i��²¥`*�¸`­���E`�\idk`�d��E²³`°pC`�\�b5�E`�dfehgibjdk`£�EnqpÄ`o��·ÒpCgi�E`��E²Ð\§b ÉÆõ ͵g�ä�`��B©âï6ï£ð5Ï^�¨�³��®*«Ò[ õ Î ò�]¾Ï\§bÐ�Ê�³��l ¢ θï°b5�¾²³`ogi�E²³`��&²j\§bj��ÏÐ�B¦�©âï6ï£ð nqbj���E`�\idk`�dG�E²³`�pÄ`�\§b6�E`­dkejg3bjdf`¬�¾nqpC`&�¸·¨g§ä�`Ç� ÉÆõ Íñ¿�²¥`�b�E²¥`¯gib³¦.�hgÆ\§�Ñ�apC`�pCgi�E·(\3����d�\3d°\(dknqpÄe³¤q`°�³�¸û�`��ÇÎ

¢ g3�Ädkg3pÄ`C�E�Ñ\3��`�d�Ïodf�j��²ö\id È�� � ��Å"! Ï��E²¥`Àej`��f�.g3�¾p¶\§bj��`¶\3�¸äi\�b¸�Ñ\§±3`�g��Ò�B¦�©âï6ï£ð g§ä�`Ç�(©âï¯ï£ð\§bÐ�Ì�³��l ¢ n�d�±3�¾`�\§�¾`��°�E²j\�b�¿og3�¥¤��À�j`5`�ý�ej`����¾`��Ê�.�Eg3p �¾²³`Òn�pCe³�Eg�ä�`�p(`�b��Bnqb��Ç\3��²³`Ò²³n��¬�Ñ\§�¾`�ΰlo²³`\3d¾��`�bj��nqb³±¼g3�Ñ�¸`��5g§�¯dE��²³`��¸�³¤�nqb³±Âp¶\§n�b¸�Ñ\§n�b³`����¸·ö�B¦�©âï6ï£ð p¶\§�Ñ��²³`­d¯�E²¥`Àe¥�E`��.`��Ñ��²¥nqb³±Âbj\§�¾�³�E`Âg§��E²¥`(�¸n�df½�Ψlo²j\§�£n�d�Ï��E²³`(�¸n¹dk½å��g3b��En�b¸�³`­dÿ�¾`�\3�¸n�b³±Â�³\§�Ñ\C�h`Ç·�g3bj�a�¾²³`5`�bj�ag��°\Ê�¾`�\3�a�¾`��^�¥`�dk�ÇÏ�g§�.�¾`�bpCg�ä�nqb³±¶�E²¥`C�E`�\i�_^�¿��¾nq�¾`À²¥`�\3�I�.gi�E¿\§���Õgib³`¶g3�5pCgi�E`Ädk�³�f��\3��`�dC[.g3�5`�ä�`ÇbÌ�¾g��E²³`Cb¥`�ý¸�m��·�¤qnqbÐ�¸`���]ÑÎlo²³n¹d¯e³�¾`��.`�����²³n�b³±¶\3���Enqä�nq�f·å��g3b��En�b¸�³`­d¬�³b��Enq¤�d¾\§�En¹d �.·�nqb³±Â\Â��g3b¸Óб3�³�¾`��Ìp¶\�ý¸n�pÊ�³pìe³�E`��.`Ç����²¼dkn�Ç`Êgi�

Page 57: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É3É

�E²¥`¶�¸n�df½Ì�¾`���`�n�ä�`�d*\ab³`Ç¿ü�E`����³`�df�ú�.gi�(dk`��¾ä¸n¹��`�Îa` ��g¥Ï��E`����³`�df��d6�E²j\��(\§�E`Ĥqg3±in���\�¤q¤�·a�.g3�E¿\§�Ñ� g��6\�bnqpÄpC`��¸n�\§�¾`�¤q·6e³�¾`�ä�nqg3�Ðdo�E`�\i��¿�n�¤q¤�dk��û�`Ç�°dk²³gi�E�E`Ç�°dk`�`�½Ä�¸`�¤¹\�·³d�ÎBlo²³n�dop¶\�·(\i����g3�¥b¸�o�.gi�°dkg3pÄ`¬g����¾²³`\3�¥�¸nq�¾nqg3bÐ\§¤Gej`��k�.gi�Ep¶\�bj��`6\i��²¥nq`�ä�`��(�¸·a�B¦�©âï6ï£ðüdE��²³`��¸�³¤�nqb³±¥Î

¢ g3��\§¤�¤jdkn�ý5�E��\i��`�d�ÏÐ�B¦�©âï6ï£ð e³�Eg�ä�n��¸`­d�dk�Ñ\§�Eäi\��EnqgibC�E`­dkn�df��\�bj��`�`����³nqäi\�¤q`�b����Eg6gi�odf�³ej`��En�g3�B�Eg6�¾²³`g3�¾²³`��°df`�`�½�¦��¾`��¸�j��n�b³±¨\§¤�±3g3�¾nq�¾²³p¶d¬[�\3do`�ä�n���`�bj��`��Ò��·(nq��d�dE���j\§�¾`��¶��g�`�����nq`Çb¸�Bg§��äi\��En�\��En�g3b�]ÑÎolo²³n¹dën¹db³gi�°dk�³�¾e³�En¹dknqb¥±³Ïj\3d¬�B¦�©âï6ï£ð ¿�\3don�b¸ä�`Çb¸�¾`��m�.gi���E²³n¹doe³�³�¾ehgÆdk`�Î�´��E`���n����Ñ\§�³¤�·�Ï�©âï¯ï£ðµ²j\3d��E²³`6b³`Çý¸�²³n�±3²³`�df�°��g�`�����nq`Çb¸�B�.g3��pCgÆdk��¿ogi�E½�¤qgÆ\3�³d�ϸ�.g3¤q¤�g�¿o`��C��·Ê�Ò�¥��®*«Ò[ õ Î ò�]�\§bj���³��l ¢ Î

ÖØקÙ���Ú&Á�Û��.Ü��IÝ(��Þ�Ù!;¼àaÜ�á^Ý(Ücb ;edMd��.Üâ�¢ nq±i�³�E`­d*í¸Î�Ë õ C í¸Î�Ë�í¶�¸n�dfe³¤�\�·¶�E²¥`5pC`�\§b¶�¾`�dkejg3bÐdk`(�EnqpÄ`�d�\§bj��d¾�^�Ð\§�E`­����g�`�����nq`�b���d�g§��äi\§�¾n�\��Enqgib

�.g3�5�.�³¤�¤q¦.p¶\§eéd¾��²¥`��¸�³¤�nqb³±�g��Ò�¾²³`Âdkn�ý÷�¾��\i��`�d�Î ¢ � ¢ �ê\�bj�ö�E²³`©Gª�«¬¦.�j\idk`��ß�B¦�©âï6ï£ð \�¤q±ig3�En��E²³p\§�¾`(\§¤¹dkg¶df²³g�¿�ba�.g3�6��gipCej\��En�dfg3bÂe³�³�EejgÆdk`�d�Î ¢ �³¤�¤q¦.p¶\§eÂdE��²³`����³¤qn�b³±Ên�pCe³�¾g§ä�`­dë�E²¥`Òej`��k�.gi�Ep¶\�bj��`¨g§�©âï6ï£ðæÏ��Ò�³��®*«¨[ õ Îóò^]ÑÏâ\�bj�÷�³�^l ¢ �.g3�m\§¤q¤B�¾��\3��`�d¯`�ý¥��`�e¥� ��� ����� Î�lo²¥n�d*nqpCe¥�Eg�ä�`�pC`�b¸�°n�d*b³gi�Ò�¾²³`�E`­dk�³¤��Òg§�£�E`­�¸�j��`��êdk`�`�½¼�En�pC`�d¬ä�n�\a�j`��¾�E`��¨p¶\§e¥e³nqb³±Ânqb¸�.gi�Ep¶\��En�g3bGÏ��³�³�Ò�Ñ\§�¾²³`��5n�d¨��\§�Ðdk`��Õ��·Ì�¾²³`²³`��¥�En�df�En¹�Ò�jdk`����EgådE��²³`��¸�¥¤q`5�E`­�^�³`­dk��d*¿�n��E²³n�b¼\adkn�b³±3¤�`C��·¸¤�nqbj�¸`Ç��Î5®*d6�¸`­dE���¾nq�j`���nqb¼dk`­���En�g3b É Î È ÎqËiÏ\Ê�.�³¤q¤�¦�p�\§e¼dE��²³`����³¤q`��°�jdf`�dæ�B¦�©âï6ï*ð5Ï�©âï6ï£ðæÏG�Ò�¥��®*«Ò[ õ Î ò�]�Ï�gi�æ�¥��l ¢ ¿�²³`�b¼pCg�ä�nqb³±(�j`��f¿o`�`�b��·�¤qn�bj�¸`��Ñd�\§bj�(�jdk`�do�B¦�©âï6ï*ð��E¿�n��E²³n�b9�6\Ò��·�¤qn�bj�¸`��ÇÎâlo²¥`��E`��.gi�E`�Ï��¾²³`ÿ�.�¥¤q¤q¦.p¶\�e5ä�`���dfnqg3bÐd»g���©âï6ï£ð5Ï�Ò�³��®£«Ò[ õ Î ò^]ú\§bj�ö�³�^l ¢ �jdk`¶�¾²³`Ce³�¾`��.`�����²³n�b³±Â��\3��²³`Cp(�j��²�pCg3�¾`Ê`�û�`����Enqä�`Ǥq·a�¾²j\§bé�¾²³`�nq�¨©Gª�«¬¦�j\idk`��Â��g3�³b��E`Ç�Eej\��E��d�Î

lîg¨ä�`��EnÃ�.·Ò�¾²³`¬�¾`�¤�\��En�ä�`�nqpCejg3�¾��\�bj��`�g§���¾²³`Ò�B¦�©âï6ï*ðñ²³`Ç�³�En¹dk�En¹����g3pÄej\§�¾`��æ�¾gÒ�¾²³`ÿ�.�¥¤q¤�©Gª�«¬¦.�Eg3¦´Bª�«çp¶\�e³e³n�b³±³Ï³�¾²³`5d¾��²³`­�¸�³¤qn�b³±(\§¤�±3gi�Enq�¾²³p¶do¿�`��E`¨�E`�pCejgi��\§�¾nq¤�·ÊpCg���nèÓj`��¶�Eg(�jdk`m\æÓjý�`��Àb��³p(�j`��g§�df`����Egi��d*ej`��6��·�¤qn�bj�¸`��6[¾Ë õ ò É ]£��\��E²³`��£�E²j\�b��E²³`(\i���E�j\�¤ �gib³`�¦��¸`�ej`�bj�¸`Çb¸�*äi\�¤q�³`�d�Î6lo²³`5�E`­dk�³¤��Enqb¥±ej`��k�.gi�Ep¶\�bj��`Ò�.gi�5\§¤�¤��E�Ñ\3��`­d¯\�bj�Õ\�¤q±3gi�En��E²³p¶d*n¹dú¿�n��E²³n�bé˧Íôg§��E²³`(ej`��k�.gi�Ep¶\�bj��`5g3�¥��\§n�b³`��Ì�Ðdknqb¥±\3�Ç���³��\��E`*p�\§e³e³n�b³±�d�Î�lo²��jd�ϳ�¾²³`£dk`�`�½�¦.�E`��¸�Ð��nqb³±m\§¤�±3g3�¾nq�¾²³p¶d�g3�³�Ñ\§n�bÀgib³¤q·(\Òp�\§�E±inqbj\�¤j�h`Çb³`�Ój�B�.�Eg3p\3�Ç���³��\��E`¨©Gª�«¬¦.�Egi¦�´Bª�«ñp¶\§e¥e³nqb³±Ædo¿�²³`�bÂdE��²³`����³¤qn�b³±5�E²³`6�¾`�\§¤�¦�¿�g3�E¤¹�C�E��\i��`�d�Î

ªo`���\��jdk`*g����¾²³`6²³`��³�¾n�df�En��iÏ^�¾²³`*pC`­\§bC�¾`�dkejg3bÐdk`6�En�pC`�d�g§���.�³¤q¤�¦�p�\§eÄ©âï¯ï£ð5ϳ�Ò�³��®£«Ò[ õ Î ò^]ÑÏ�\§bj��³��l ¢ pCg3�¾`*��¤�g�df`�¤q·¨p¶\§�Ñ��²(�E²j\��og��B�B¦�©âï6ï£ð5Î ¢ g3���E²³`¬ÓÐä�`¬¿�g3�E½�¤qgÆ\3�³dB¿�²³`��¾`Ò�B¦�©âï6ï£ðçe¥�Eg�ä¸n¹�¸`�d�E²¥`5�h`­dk�6pC`�\�ba�E`­dkejg3bjdf`Ê�¾nqpC`Æϳ�E²³n¹d¬nqpCe¥¤qnq`­donqpCe³�¾g�ä�`��Êej`��k�.gi�Ep¶\�bj��`Ò�.gi�6©âï6ï*ð5Ï��¨�³��®*«Ò[ õ Î ò�]�Ï\§bÐ� �³��l ¢ Î 0¬g�¿o`Çä�`���ÏB�B¦�©âï6ï£ð nq�Ñdk`�¤Ã�°g3�³�Ñ\§nqbÐdÒg3b³¤�·é\ap¶\§�¾±3n�bj\§¤��E`��¸�Ð���En�g3bénqbÕpÄ`�\§bÕ�¾`�dkejgibjdk`�En�pC`(�jdkn�b³±Õ\i�����³�Ñ\§�¾`a©Gª�«°¦��¾g3¦�´ëª�« p¶\§e³e¥nqb³±Ædgf�\i�³�¸nqb¥±Ì�¾²³`��B¦�©âï6ï£ð ��·�¤qnqbÐ�¸`��6²³`��³�¾n�df�En��Ä�¸g�`�d¤qn��E�¾¤q`*�¾g5pCg��¸nè�.·(�E²¥`¯�j`�²Ð\­ä�nqgi��g§�B�¾²³`¨©Gª�«¬¦.�j\3df`��a�B¦�©âï6ï£ðü\§¤�±3g3�¾nq�¾²³p�Î

¢ �³¤q¤�¦�p¶\�eÌ�³�^l ¢ nqpCe¥�Eg�ä�`�do¤q`­dEd*�E²j\�bI�.�¥¤q¤q¦.p¶\�e�©âï6ï£ð g3�¨�Ò�³��®*«Ò[ õ Îóò^]�¿�²³`ÇbÕ��gipCej\��E`��a�¾g�E²¥`*©Gª�«¬¦.�j\idk`��(\§¤�±3g3�¾nq�¾²³p¶d�Î ��b5�E²³`£��\3df`¬g�� È�� � ��Å"! Ï3�E²¥`*©Gª�«¬¦.�j\idk`��C�³��l ¢ dE��²³`��¸�¥¤q`���n¹dB\3���¾�j\§¤�¤q·dk�¥eh`Ç�Enqgi�Ò�¾gÀ�¾²³`5�.�³¤q¤�¦�p¶\�e�ä�`���dfnqgibGÎ(lo²³n�d*n�d*�j`���\��jdk`Äg§�°\Âdk¤�nq±3²��¨�¸nèû�`��¾`�bj��`5n�bÌ�¾²³`(`�ý³\i���*n�pCe³¤q`ǦpC`�b���\��En�g3b¶g§�B�¾²³`C�³��l ¢ dE��²³`��¸�¥¤q`��ÇÎú�¥��l ¢ �Ñ\§½�`�d��E²³` �E¤¹\3dk�£½¸b³g�¿�b�ejg�dfnq�¾nqg3b �Êg§���E²¥`Ò�E`­\3�_^Ç¿��Enq�¾`²³`�\i�é\3dÒ�j`�nqb¥±3hf�jdf�5�h`Ç·�g3bj�Ì�¾²³`C¤¹\3dk�5�¥¤qg���½Ìg��*�¾²³`CnqpÄpC`���n�\§�¾`�¤Ã·ae³�¾`�ä�nqg3�Ðd¯�E`­�^�³`­dk��μ�B¦�©âï6ï£ð5Ï©âï6ï£ðæÏB\�bj�÷�¨�³��®*«Ò[ õ Î ò�]6�jdk`Â�E²³`CÓj�Ñdk�(�³¤qg���½Õg��6�E²³`¶e³�¾`�ä�nqg3�ÐdÒ�E`����³`�df�5nqbjdf�E`�\i��Îölo²¥n�d5½�`�`�ejd�E²¥`Ò�E²¥�E`�`¨dE�Ç\§b³b³n�b³±¶\�¤q±3gi�En��E²³p¶dë�.�¾g3pôdk�Ñ\§�¾ä¸n�b³±Êg�ä�`��¾¤�\�e³e³nqb¥±Ê�¾`��^�¥`�dk�Ñd�Î ¢ �³¤�¤q¦.p¶\§ea�¥��l ¢ \3��²³nq`Çä�`�d\Cej`��k�.gi�Ep¶\�bj��`5nqpÄe³�Eg�ä�`�p(`�b���`����³nqäi\�¤q`�b��¬�¾gC�.�³¤q¤�¦�p¶\�e�©âï6ï£ð \§bj���Ò�³��®*«¨[ õ Îóò^]�nÃ��nq�6\�¤�dkgÂ�jdk`­d

i jlk/m7npo qgrDrQs"nutOvgw/m;wTm;xWn/y�xWz{t-xWz s1|/}Wm�t<~e}Wm;nTy@�)k-�Ft-m7}�s+�-z�q1���%m;nFq/o;o�w/�D|>m;����m;m;n��)m�sgt-xWn/y��)k/m'}Ns1z%���%m�vgw/m;z)�%m�tz)m+o �)qg�����)qgr��)kTm�rDm+t-xNs�s"nut��)m+o m;xW�-xanTy�sGn/m;���)m�vgw/m;z%�B�)qUz%m;�)�-xNo m@���Ixa�%z)�+~@�%k/m�t-xWz%���%��s1nTz���m;�%zBq@n/mBqg�\r�q@�%m\�%m�vgw/m;z)�%m�tz)m+o �)qg�)ze�)qM�)k/m�kTq@z)�_���>m;�)k>s1�/z�s+���)m;�I��s"xa�%xWn/y���q@�<�>m;�)r�xaz%z)xWq@nG�%qBw/z)m��)k/m_�um;�%xW�/k/m;� s1}-|/w/z �Js1n>tG�um7����qg�)rDzJs"n-��n/m�o�m;z)z s1�)�o }Wm�s"n�wT�u�@o qgrD�/}Wm;�%xWq@n'�/�)q/o m7z)z)xWn/y>���B���%m;��s@o%�-n/q1�B}Wm�t-ygxWn/y��)k/mDo�q@rD�T}am7�)xWq@n'rDm7z)z�s"y@m@~��)k/m�k/q@z%�Gq@|/� s1xWn/zG�um7�)rDxWz%z)xWq@n�)q�wTz)mG�)k/m |/w/z�s1n>tD�%��s"n/z���m7�)z�s�nTm;�¡�%m�vgw/m;z%���%q��%k/m�t-xWz%�¢�

Page 58: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É í

£ £ FCFS¤ ¤ C-LOOK (LBN)¥ ¥ C-LOOK (MAP)¦ ¦ LOOK (MAP)§ § VSCAN(0.2) (MAP)¨ ¨ SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

© © © © ©©©©

ª ª ª ª ª ª

ª

ª ª ª ª ª ª

ª

« « « « « «

«

¬ ¬ ¬ ¬ ¬ ¬

¬

­ ­ ­ ­ ­ ­

­

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

® ® FCFS¯ ¯ C-LOOK (LBN)° ° C-LOOK (MAP)± ± LOOK (MAP)² ² VSCAN(0.2) (MAP)³ ³ SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0.0

|U2.5

|U5.0

|U7.5

|U10.0

|U12.5

|U15.0

|U17.5|U20.0

Trace Scaling Factorq

Squ

ared

Coe

ffic

ient

of V

aria

tion

´ ´´´ ´ ´ ´ ´

µ µ µ µµ

µ

µ

µ µ µ µµ

µ

µ

¶ ¶ ¶ ¶¶

· · · ··

·

·

¸ ¸ ¸ ¸ ¸¸

¸

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ�������)$J¹G¡4������� ����¢ �³¤q¤�¦�_�\�e¶\§bj�©Gª�«¬¦�ª�\3dk`­�À®°¤q±3gi�En��E²³p ´�`��k�.gi�Ep¶\�bj��`

Page 59: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É þ

º º FCFS» » C-LOOK (LBN)¼ ¼ C-LOOK (MAP)½ ½ LOOK (MAP)¾ ¾ VSCAN(0.2) (MAP)¿ ¿ SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

À À À À ÀÀ

À

Á Á Á Á ÁÁÁ

Á

Á

Á Á Á Á ÁÁÁ

Á

Á

    ÂÂÂ

Â

Â

à à à à ÃÃÃ

Ã

Ã

Ä Ä Ä Ä ÄÄÄ

Ä

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

Å Å FCFSÆ Æ C-LOOK (LBN)Ç Ç C-LOOK (MAP)È È LOOK (MAP)É É VSCAN(0.2) (MAP)Ê Ê SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0.0

|U2.5

|U5.0

|U7.5

|U10.0

|U12.5

|U15.0

|U17.5|U20.0

Trace Scaling Factorq

Squ

ared

Coe

ffic

ient

of V

aria

tion

Ë Ë Ë

ËË Ë

Ë

Ì Ì Ì

ÌÌ

Ì Ì Ì

Ì Ì Ì

Ì

Ì

Ì Ì ÌÌ

Í Í Í

Í

Í

ÍÍ Í

Í

Î Î Î

Î

Î

ÎÎ Î

Î

Ï Ï Ï

Ï

Ï

ÏÏ

Ï Ï

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

�����9Á��§�Ì���)$�$h¡ �å �¢¤£ ����¢ �³¤q¤�¦�_�\�eÂ\§bj�©Gª�«¬¦�ª�\idk`��¶®¬¤�±3gi�Enq�¾²³pì´â`��k�.gi�Ep¶\�bj��`

Page 60: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É �

Ð Ð FCFSÑ Ñ C-LOOK (LBN)Ò Ò C-LOOK (MAP)Ó Ó LOOK (MAP)Ô Ô VSCAN(0.2) (MAP)Õ Õ SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

Ö Ö Ö Ö ÖÖ

Ö

Ö

× × × × ××

×

×

× × × × ××

×

×

Ø Ø Ø Ø ØØ

Ø

Ø

Ù Ù Ù Ù ÙÙ

Ù

Ù

Ú Ú Ú Ú Ú

Ú

Ú

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

Û Û FCFSÜ Ü C-LOOK (LBN)Ý Ý C-LOOK (MAP)Þ Þ LOOK (MAP)ß ß VSCAN(0.2) (MAP)à à SSTF (MAP)

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00|º128.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

á áá

áá

á á á

â ââ

ââ

â â â

â ââ

ââ

â â â

ã ãã

ãã

ã ã ã

ä ää

ää

äää

å åå

åå

åå

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

�����9Á��§�����%$³��¡%Ã�ÄÆÅ�ÇÉÈ%ÊÌË �B¢ �¥¤q¤q¦�_�\§e�\§bj�©Gª�«¬¦�ª�\idk`��¶®¬¤�±3gi�Enq�¾²³p ´â`Ç�k�.g3�¾p¶\§bÐ��`

Page 61: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É�¥

æ æ FCFSç ç C-LOOK (LBN)è è C-LOOK (MAP)é é LOOK (MAP)ê ê VSCAN(0.2) (MAP)ë ë SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

ì ì ì ì ì ì ìì

ì

í í í í í í í í í

í

í

í í í í í í í íí

í

í

î î î î î î î îî

î

î

ï ï ï ï ï ï ï ïï

ï

ï

ð ð ð ð ð ð ðððð

ð

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

ñ ñ FCFSò ò C-LOOK (LBN)ó ó C-LOOK (MAP)ô ô LOOK (MAP)õ õ VSCAN(0.2) (MAP)ö ö SSTF (MAP)

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00

|º128.00

|º256.00|º512.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

÷ ÷÷

÷÷÷ ÷ ÷

÷

ø ø øø

øø

ø ø ø ø ø

ø ø øø

øø

ø

ø

øø

ø

ù ù ùù

ùù

ù

ù

ùù

ù

ú ú úú

úú

ú

ú

úú

ú

û û ûû

ûû

û

ûû û û

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ�������)$(hG¡%�åäÄ�Çæç� ��¢ �³¤�¤q¦�_�\§eÂ\§bj�©Gª�«¬¦�ª�\3dk`­�À®°¤q±3gi�En��E²³pì´â`��f�.g3�Ep�\§bj��`

Page 62: Aggressive Centralized and Distributed Scheduling ofDisk Requests

É �

ü ü FCFSý ý C-LOOK (LBN)þ þ C-LOOK (MAP)ÿ ÿ LOOK (MAP)� � VSCAN(0.2) (MAP)� � SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

� � � �

� � � � � ��

� � � � � ��

� � � � � �

� � � � � �

� � � ��

��

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

� � FCFS� � C-LOOK (LBN) C-LOOK (MAP) LOOK (MAP)� � VSCAN(0.2) (MAP)� � SSTF (MAP)

|÷0.125ø |÷

0.250ù |÷0.500ú |÷

1.000û |÷2.000û |÷

4.000û|ü0.25

|ü0.50

|ü1.00

|ü2.00

|ü4.00

|ü8.00

|ü16.00

|ü32.00|ü64.00

Trace Scaling Factorý

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE!

��

�� � � � �

��

�� � � � �

��

�� � � �

��

� �

� �

��

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ���I���)$ « ¡ � Å+� � Å��B¢ �³¤q¤�¦�_�\�e¶\§bÐ�a©Gª�«¬¦�ª�\3df`��¶®¬¤q±ig3�En��E²³pì´â`��f�.g3�¾p¶\§bj��`

Page 63: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í õ

� � FCFS� � C-LOOK (LBN)� � C-LOOK (MAP)� � LOOK (MAP)� � VSCAN(0.2) (MAP)� � SSTF (MAP)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

� � � � �

� � � � ��

��

� � � � ��

��

� � � � ��

� � � ��

� � � ��

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

� � FCFS� � C-LOOK (LBN)� � C-LOOK (MAP) LOOK (MAP)! ! VSCAN(0.2) (MAP)" " SSTF (MAP)

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00

|º128.00

|º256.00|º512.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

#####

#

$$ $ $

$ $ $ $ $$

$$ $ $

$ $ $ $ $$

%% % %

% % % % %

&& & &

&

& & & &

'' ' '

'

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ�������)$³��¡%È1� � ��Å1!É�&¢ �³¤q¤�¦�_�\�e¶\§bj�©Gª�«¬¦�ª�\3dk`­�À®°¤q±3gi�En��E²³p ´�`��k�.gi�Ep¶\�bj��`

Page 64: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í¸Ë

�E²¥`úÓÐ��dk�°�³¤�g���½Cg��B�E²¥`¯e¥�E`�ä�nqgi�jdo�E`����³`�df��ÎBlo²³n¹dÿn�bj�¸n¹��\§�¾`�do�E²j\��¬g�ä�`��¾¤�\�e³e³nqb¥±Ò�E`­�^�³`­dk��do`Çý¸n¹dk��nqb¶�¾²³``�ý�ej`��En�pC`�b���\§¤B¿�g3�E½�¤qgÆ\3�³d�Îñ��g3pC`C�.�Ñ\3���¾nqg3b g§�6�¾²³`�df`a�E`­�^�³`­dk��d(\§�¾`��¸n��E`����E¤q·ê\§�¾�E�¾nq�³�³�Ñ\§�³¤�`a�¾gÌ�¾²³`��²³g�df`�b¶pC`��E²¥g��¸g3¤�g3±3·å[�n�Î�`�ÎqÏ�d¾��\§¤�nqb³±5g��B�E�Ñ\3��`��Cn�b¸�¾`���\��E�En�äi\§¤��¾nqpC`­d�]�Î

¢ g3� ������� � ÏB©âï¯ï£ð5Ï��Ò�¥��®*«Ò[ õ Î ò�]�Ï�\§bj�Õ�³��l ¢ �¸`����E`�\idk`5nqb¼ej`��k�.gi�Ep¶\�bj��`¨¿�²³`�b¼�jdkn�b³±Â\��.�³¤�¤q¦p¶\�e¼dE��²³`��¸�³¤�`���Î5��n�bj��`Ò¤¹\§�¾±3`(�³�³��df��d*g§�¿��En��E`(\3���Enqä�nq�f·Â�¸gipCnqbj\��E`¨�E²³n¹dú�¾��\i��`�Ï�n��*n�d*¿��En��E`5�¾`��^�¥`�dk�ej`��k�.gi�Ep¶\�bj��`(�E²j\��5�¸`Ç�E`��¾pCnqb³`­d*\§¤�±3g3�¾nq�¾²³p `�û�`­���En�ä�`�b³`�d¾dæ[�\3d6pC`�\3df�³�E`­�I��·Õdf�³�jdf·³df�E`�p pC`��¾�En��Çd�]�΢ g3�Bdf`����³`�b��En�\�¤¸¿��¾nq�¾`�dâ�Eg¨\6�¸n¹dk½Ò¿�n��E²³gi�³��¿��¾nq�E`�e¥�E`��³��û�`Ç�Enqb¥±Ê[��¸`�d¾���En��h`­�¯nqb(df`����¾nqg3b É ÎqËiÎ ò^]ÑÏ�n�dEdf�³nqb¥±�E`­�^�³`­dk��d�n�bÒ¤�g3±3n¹��\§¤�¤q·£\3d¾��`�bj�¸n�b³±°g3����`����Ç\§b¨\3���¾�j\§¤�¤q·6��`�±3�Ñ\3�¸`�eh`Ç�k�.g3�¾p¶\§bÐ��`�ÎGºß²³`�bm\ÿ¿��¾nq�E`B�¾`��^�¥`�dk���gipCe³¤q`Ç�E`�d�Ïj\C�¸n�df½Âdk`�bj�¥d*\C��gipCe³¤q`Ç�Enqgib¶pC`�dEd¾\§±i`Ò�j\i��½¶�EgÄ�E²³`¨²³g�df��ÏG¿�\�nq��d��.g3�°�E²³`5b³`Çý¸�°�E`����³`�df��Ï\§bÐ�Ê�E²³`ÇbÊej`��f�.g3�Ep�d»�¾²³`°b³`���`�d¾dE\��E·(��gipCp¶\§bÐ�Ònqb³n��En�\��En�g3b5e³�¾g���`�dEdfnqb³±¥Îo®����¾²³`*d¾\§pC`°�En�pC`�Ï��E²³`°²³gÆdk�e³�¾g���`�dEdf`�dÊ�¾²³`���gipCe³¤�`��En�g3bépC`�d¾dE\§±i`�Ïon¹dEdk�¥`�dæ�¾²³`�b³`�ý��Â[�dk`­�^�³`Çb¸�¾n�\§¤.]6¿��En��E`a�¾`����³`�dk�ÇÏ�\§bÐ�ö�h`DZ3nqbÐd�E�Ñ\§bjd��.`��E�¾nqb³± �³\���\é�³¤qg���½³d(�Egö�¾²³`�g3b¥¦��jg�\����µ�³\���\ö�Ç\3��²³`a�.g3�Âdk�¥�jdk`����³`�b��C�¾��\§bÐd �.`��Â�Egé�E²³`¼��n�dk½pC`���n�\¸Î&Ŭ�³�¾nqb³±5�¾²³`�dk`¨df�E`�ejd�ϳ�E²³`¨\i���En�ä�`¬�¾`�\3�_^Ç¿��En��E`6²³`�\i�À�Egi��\��E`�do�j`�·�gibj�À�¾²³`¬Ój�Ñdk�£dk`����¾g3��g����¾²³`b³`�ý��°�E`����³`�df��Î�®*dEdf�³pCnqb¥±5�E²j\��*�E²³`m��g3pÄe³¤q`��¾nqgib¶\§bj�¶nqb³n��En¹\§�En�g3b¶e³�¾g���`�dEdfnqb³±Ä��\§½�`­dÿgib³¤q·Â\Ò�.��\3���Enqgibg§�ë\Ò�Eg3�Ñ\§�¾nqg3bØÏh�¾²³`6b³`�¿ù�E`����³`�df��nqbj���¥��do\�¤qpCgÆdk�°\Ò�.�³¤q¤��Egi��\§�¾nqgibag§�&¤�\��E`�bÐ��·�Î

lo²³`a�¾`�¤�\��En�ä�`¶dk�Ñ\§�Eäi\��Enqgibù��²Ð\§��\i���E`Ç�En�df�En¹��dÒg§�6�¾²³`À�.�¥¤q¤q¦.p¶\�eöd¾��²¥`��¸�³¤�nqb³±¼\�¤q±3gi�En��E²³p¶dÒ±i`�b³`��Ñ\§¤�¤q·p¶\�����²÷�¾²³g�df`�g§�¨�E²¥`�©Gª�«¬¦.�j\3df`��ß\§¤�±3gi�Enq�¾²³p¶d�Î ¢ gi�C�E²³` �åäÄ�Çæç� �E�Ñ\3��`ÆÏÿ²¥g§¿�`�ä�`��ÇÏë�¾²³`a�.�³¤q¤�¦�p�\§e�B¦�©âï¯ï£ðø\§¤q±ig3�¾nq�E²¥pÔ²j\3dogib³¤q·�\Òp¶\§�¾±3nqbÐ\§¤�\3�¸äi\�b¸�Ñ\§±3`¨nqbC�¾`�dkejgibjdk`¨�EnqpÄ`�ä3\��En¹\§bj��`6g�ä�`����E²³`*gi�E²³`Ç�\§¤�±3gi�Enq�¾²³p¶d�Î ��ba��\3����Ï��³��l ¢ ²j\id6\Àdfp¶\§¤�¤q`��£dE���j\��E`�����g�`��¶��n�`�b��¬g���äi\§�¾n�\§�¾nqgibÌ�¾²j\§bé�B¦�©âï6ï£ð �.gi��E²¥`ʲ³`­\­ä�nq`­dk�°¿og3�¾½¸¤�g�\i�³dÊ[�\§¤q�¾²³g3�¥±3²Õn���d¬�¾`�dkejg3bÐdk`C�¾nqpC`¨ä3\��En¹\§bj��`5n¹d6dk�En�¤q¤�±i�E`�\��E`���]�Î(ªo·�d¾\§�¾n�d �.·�nqb¥±\§¤�¤j�E`����³`�df��d�¿�nq�¾²³nqbÄ\Ò��·�¤qn�bj�¸`����j`��.g3�¾`*pCg�ä�nqb³±*�¾g5\�b³g3�¾²³`�����·¸¤�nqbj�¸`Ç��Ï��E²³`��.�³¤q¤�¦�p�\§e(\§¤�±3gi�Enq�¾²³p¶dB\§�¾`dk¤�nq±i²¸�¾¤q·(¤q`�d¾do�E`�dfn�dk�Ñ\§b����EgÄdk�Ñ\§�Eäi\��EnqgibGÎ

ÖØקÙ���Ú&Á�Û��.Ü��IÝ(��Þ�Ùß�/Á�Û�Û�àÂÜâá�Ý(Û���Ú��h�¢ nq±i�³�E`­dCí¸Î�Ë�þ C í¸Îóò¸ËÕdf²³g�¿ �¾`�dk�³¤���dæ�.gi�C`�ý�ej`��En�pC`�b���dÒ�jdfnqb³±Õ�¾²³`Õ��´Bl ¢ ¦.�j\3df`��ñ\�¤q±3gi�En��E²³p¶d(�¸`�¦

dE���Enq�j`��Cn�b�dk`­���En�g3b É Î È ÎqËiÎolo²¥`�dk`m\§¤q±ig3�¾nq�E²¥p¶do²j\�ä�`6�hgi�E²å\§b�\i�¸äi\§b���\�±3`(\§bÐ�a\(�¸n�d¾\3�¸äi\§b���\�±3`5g�ä�`���B¦�©âï¯ï£ð5Î�lo²³`\3�¸äi\�b¸�Ñ\§±3`�n¹dâ�E²¥`og3��ä�nqg3�Ðdîn�pCe³�Eg�ä�`�p(`�b��jnqbÒejgÆdknq�¾nqgib³nqb³±£�EnqpÄ`�e³�E`­�¸n����¾nqgibÒ\i�����³�Ñ\3��·�¸�³`��¾g6�E²³`°nqbj��¤q�jdfnqg3b¨g§�Ø�Eg3�Ñ\§�¾nqg3bÐ\§¤j¤�\��E`�bj��·Ònqb��.g3�Ep�\§�En�g3bGÎ�®÷�.�³¤�¤³�Egi��\��Enqgibæ�.gi��\§b 0*´ ��òiò ÉÆõ dk`��¾nq`�d�¸n¹dk½���\�½�`�d6\§e³e¥�Eg�ý¸n�p¶\§�¾`�¤q·¼ËiËÊp¶d�Ïî`­�^�³n�äi\§¤q`Çb¸�°�Egå\adk`Ç`�½ag��°g§ä�`Ç�6í3í õ ��·�¤qn�bj�¸`��ÑdÒ[�gi�5ò � Í g����¾²³`p¶\�ý¸n�pÊ�³p dk`�`�½(��n�dk�Ñ\§bj��`3]�Î ¢ g3��¿ogi�E½�¤qg�\i�³dë¿�n��E²¶\¨dk½�`�¿�`��(�¸n�df�E�En��³�³�¾nqg3bÄg§���E`­�^�³`­dk��dk�Ñ\§�E�¾nqb³±¨¤qg���\�¦�En�g3bjd*[.n�Î�`�ÎqÏ�¿�nq�¾²Âdk²³gi�E�E`Ç�°\­ä�`Ç��\§±i`¨dk`�`�½Ä�¸n¹dk��\�bj��`�d�]�ϳ�¾g3��\��En�g3bj\�¤G¤�\§�¾`�bj��·(�E`Çe³�E`�df`�b���d�\§b¶`�ä�`ÇbC¤�\��E±3`Ç��.��\i���En�g3b(g§�Ø�E²³`��¾g3��\�¤jehgÆdkn��Enqgib³nqb¥±¯�¾nqpC`ÆÎGlo²³`£�¸n�d¾\3�¸äi\§b���\�±3`*n¹dâ�E²Ð\§����´Bl ¢ ¦.�j\3df`��C\§¤�±3gi�Enq�¾²³p¶dâ²Ð\­ä�`b³g¶nqb¥²³`��E`Çb¸�°�³n�\id¬�Eg�¿\§���¥d¯df`��Eä�n���nqb³±Ädk`����³`�b��En¹\§¤��E`�\i�³d¬n�b�¤qg3±in���\�¤q¤�·a\idE��`Çbj�¸nqb¥±Àgi���¸`Ç��Ψ®¬bÕ��´Bl ¢dE��²³`����³¤q`���df`�¤q`�����d��E`����³`�df��dB�j\3df`��Cg3b¶�E²³`Çnq�Be³�E`­�¸n����¾`��5ehgÆdkn��Enqgib³nqb¥±5�EnqpÄ`�Ï3b³gi���E²³`�n���©Gª�«ßg3�°��·�¤qn�b³¦�¸`��ÇÎ 2�ä�`�bÌ�^´��l ¢ gib³¤q·�dk`��¾ä¸n¹��`�d�dk�¥�jdk`��Ñd¬g§�ë\Cdk`����³`�b��En¹\§¤Ødk�E�¾`�\§p n�ba¤qgi±3n¹��\§¤�¤q·¶\idE��`�bÐ�¸nqb³±(g3�Ñ�¸`��Çή*d�\5�E`�df�³¤q�Çϳ�E²³`(��´Bl ¢ ¦.�j\3df`��a\�¤q±3gi�En��E²³p¶do�¥�Enq¤�n��`£e³�E`��.`Ç����²³nqb³±m��\3��²³`�do¤�`�dEd�`�û�`����¾nqä�`�¤�·�Î�lâ\��³¤q`mí¸Î Ȥqn¹dk�Ñd¯�E²¥`C��\i��²¥`ʲ³n��Òej`��Ñ��`�b���\§±i`�dú�.gi�5dfg3pC`ÄdE\�pCe³¤q`(�E�Ñ\3��`ÄdE�Ç\§¤qn�b³±À��\i���Egi��d�Î�«¬g3�¾`C�E²Ð\§�Ê�B¦�©âï6ï£ð\§¤�¿�\�·¥do`�ý¸²¥nq�³n���do\5²³n�±3²³`��°�Ç\3��²³`*²³n�����\§�¾`�Î

lo²³n�d6�E�Ñ\3�¸`�g�û \­û�`����Ñd¯g�ä�`���\�¤q¤�ej`��k�.gi�Ep¶\�bj��`(�EgÂ�¸nèû�`��¾`�b��Ò��`�±3�¾`�`�d¬�.g3�6`�\i��²¼g§�°�¾²³`Cdfnqý��¾��\3��`�d�΢ g3� ������� � Ï��E²³`(��´Bl ¢ ¦.�j\3df`���\§¤�±3g3�¾nq�¾²³p¶d�\§�¾`5��¤�`�\§�¾¤q·¶df�³ej`��En�g3�°�Eg(�E²³`mdk`�`ǽ¸¦.�E`����j��nqb¥±(\§¤q±ig3�¾nq�E²¥p¶d�Î��\3��²³`6½�b³g�¿�¤q`��¸±i`6nqbj���¾`�\3df`�doej`��k�.gi�Ep¶\�bj��`6\�b�\i�³�¸nq�¾nqgibj\§¤&í C Ë�í^Íü�.gi�¬�¾²³`6¤�\§�¾±3`�df�*d¾��\§¤�nqb³±Ò��\i���Egi��d�Î��b¶`�ý¸ej`��¾nqpC`Çb¸�Ñd»�Ðdknqb¥±Ê�¾²³`Ògi�E²³`���Ójä�`6�E�Ñ\3��`­d�ϳ�E²¥`Ò��g3pCej\��En¹dkg3b¶n¹dÿb³gi�*\id¬df�E�Ñ\§nq±i²¸�f�.g3�¾¿�\§�Ñ��Î*��´Bl ¢dE\��E�³�Ñ\§�¾`�dÒpCg3�¾`(�^�¥n���½¸¤�·À�¾²j\§bß�B¦�©âï6ï*ð5Ï��³�³�5��´Bl ¢ e³�¾g§ä�n���`�dÒdf�³ej`��En�g3�Òej`��f�.g3�¾p¶\§bj��`Ò�.g3�5dfg3pC`dk�¥�³¦�d¾\§�¾�³��\��EnqgibÌ¿�g3�¾½¸¤�g�\3�¥d�Î ¢ gi�*`�ý¥\§pCe¥¤q`�Ï�Ój±3�³�¾`(í¸Îóò¸Ë�\¶df²³g�¿°d¬�E²j\��5��´Bl ¢ n�d��³e��Eg�Ë ¥ Íì�h`Ç�E�E`Ç�

Page 65: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í3ò

( ( FCFS) ) C-LOOK (LBN)* * SPTF+ + SPCTF, , ASPTF(6)- - ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

. . . .....

/ / / / //

/

0 0 0 0 000

0

1 1 1 1 1 111

1

2 2 2 2 2 222

3 3 3 3 3 3333

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

4 4 FCFS5 5 C-LOOK (LBN)6 6 SPTF7 7 SPCTF8 8 ASPTF(6)9 9 ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0.0

|U2.5

|U5.0

|U7.5

|U10.0

|U12.5

|U15.0

|U17.5|U20.0

Trace Scaling Factorq

Squ

ared

Coe

ffic

ient

of V

aria

tion

: ::: : : : :

; ; ; ;;;

;

< < < < < <<

<= = = = = = =

= => > > > >> > >

? ? ? ? ? ? ???

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ�������)$(ÂG¡4������� ����¢ �³¤q¤�¦�ð*b³g�¿�¤q`­�¸±3`6®°¤q±3gi�En��E²³pì´â`��f�.g3�Ep�\§bj��`

Page 66: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í È

@ @ FCFSA A C-LOOK (LBN)B B SPTFC C SPCTFD D ASPTF(6)E E ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

F F F FFF

F

G G G G GGG

G

G

H H H H HH

H

I I I I III

I

J J J JJ

J

K K K K KKK

K

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

L L FCFSM M C-LOOK (LBN)N N SPTFO O SPCTFP P ASPTF(6)Q Q ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0.0

|U2.5

|U5.0

|U7.5

|U10.0

|U12.5

|U15.0

|U17.5|U20.0

Trace Scaling Factorq

Squ

ared

Coe

ffic

ient

of V

aria

tion

R R R

RR R

R

S S S

SS

S S S

T T TUTV V V

V

V

W W WX X XXX

X

X X

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ���I���)$�â�¡��å �¢¤£�����¢ �³¤q¤�¦�ð*b³g�¿�¤�`��¸±3`¨®¬¤�±3gi�Enq�¾²³pì´â`��k�.gi�Ep¶\�bj��`

Page 67: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í É

Y Y FCFSZ Z C-LOOK (LBN)[ [ SPTF\ \ SPCTF] ] ASPTF(6)^ ^ ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

_ _ _ _ __

_

_

` ` ` ` ``

`

`

a a a a aa

a

a

a

b b b b bbb

b

b

c c c c cc

c

c

d d d d ddd

d

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

e e FCFSf f C-LOOK (LBN)g g SPTFh h SPCTFi i ASPTF(6)j j ASPCTF(6)

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00|º128.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

k kk

kkk k k

ll

ll

ll l l

m mm

m

m mmmm

n nn

n

n nnnn

o oo

o

o oo o

p pp

p

p p pp p

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

�����9Á��§�����%$J�G¡%Ã�ÄÆÅ�ÇÉÈ%ÊÌË �B¢ �¥¤q¤q¦�ð*b³g�¿�¤q`���±3`6®¬¤�±3gi�Enq�¾²³pì´â`��k�.gi�Ep¶\�bj��`

Page 68: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í3í

q q FCFSr r C-LOOK (LBN)s s SPTFt t SPCTFu u ASPTF(6)v v ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

w w w w w www

w

x x x x x x xx x

x

x

y y y y y y y y y yy

y

y

z z z z z z z z z zz z

z

z

{ { { { { { { { {{{

{

| | | | | | | | | ||||

|

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

} } FCFS~ ~ C-LOOK (LBN)� � SPTF� � SPCTF� � ASPTF(6)� � ASPCTF(6)

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00

|º128.00

|º256.00|º512.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

� ���

�� �� �

� � ��

��� � �

� �

� � � � � �� ����

� � � � � �����

� �

��

� � � � � �� ���� �

� � � � � �� � �

���� �

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ�������)$J�G¡%�åäÄ�Çæç� �G¢ �³¤q¤�¦�ð*b³g�¿�¤q`­�¸±3`6®°¤q±3gi�En��E²³pì´â`��f�.g3�Ep�\§bj��`

Page 69: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í3þ

� � FCFS� � C-LOOK (LBN)� � SPTF� � SPCTF� � ASPTF(6)� � ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

� � � �

� � � � � ��

� � � � � ���

� � � � � � ��

� � � � � � ��

� � � � � � ���

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

� � FCFS� � C-LOOK (LBN)� � SPTF� � SPCTF� � ASPTF(6)� � ASPCTF(6)

|÷0.125ø |÷

0.250ù |÷0.500ú |÷

1.000û |÷2.000û |÷

4.000û|ü0.25

|ü0.50

|ü1.00

|ü2.00

|ü4.00

|ü8.00

|ü16.00

|ü32.00|ü64.00

Trace Scaling Factorý

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE!

��

� �

��

�� � � � �

��

��

��

��

��

��

��

��

��

��

� � �

  

  

        

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ���I����� ¹î¡ � Å+� � Å��B¢ �³¤q¤�¦�ð*b³g�¿�¤�`��¸±3`ú®¬¤q±ig3�En��E²³pì´â`��f�.g3�¾p¶\§bj��`

Page 70: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í �

¡ ¡ FCFS¢ ¢ C-LOOK (LBN)£ £ SPTF¤ ¤ SPCTF¥ ¥ ASPTF(6)¦ ¦ ASPCTF(6)

|N0.125n |N

0.250o |N0.500p |N

1.000O |N

2.000O |N

4.000O|U0

|U50

|U100

|U150

|U200

|U250

Trace Scaling Factorq

Mea

n R

espo

nse

Tim

e (m

s)

§ § § § §

§

¨ ¨ ¨ ¨ ¨¨

¨¨

¨

© © © © ©©

©©

ª ª ª ª ª ªª

ªª

« « « « « ««

«

¬ ¬ ¬ ¬ ¬ ¬¬

¬ ¬¬

[�\^]_a`�\�bac�`�dfehgibjdk`mlonqpC`

­ ­ FCFS® ® C-LOOK (LBN)¯ ¯ SPTF° ° SPCTF± ± ASPTF(6)² ² ASPCTF(6)

|µ0.125¶ |µ

0.250· |µ0.500¸ |µ

1.000¹ |µ2.000¹ |µ

4.000¹|º0.25

|º0.50

|º1.00

|º2.00

|º4.00

|º8.00

|º16.00

|º32.00

|º64.00

|º128.00

|º256.00|º512.00

Trace Scaling Factor»

Squ

ared

Coe

ffic

ient

of V

aria

tion

- LO

G S

CA

LE

!

³³³³³

³

´´ ´ ´

´ ´ ´ ´ ´´

µµ µ µ

µ

µ

µ µ

¶¶ ¶ ¶

¶¶

¶ ¶

·· · ·

· ··

· ·

¸¸ ¸ ¸

¸ ¸ ¸ ¸ ¸¸

¸

[���]��^�^�j\��E`����Bg�`�����nq`�b��og�����\��En�\��En�g3b

���.�9Áâ���������\$j¡%È1� � ��Å1!É�&¢ �³¤q¤�¦�ð*b³g�¿�¤q`­�¸±3`6®°¤q±3gi�En��E²³pì´â`��f�.g3�Ep�\§bj��`

Page 71: Aggressive Centralized and Distributed Scheduling ofDisk Requests

í ¥

����\�¤q` ©Gª�«¬¦�ª�\3df`��lG��\i��` ¢ \i���Egi� �B¦�©âï¯ï£ð ��´o��l ¢ ®¯�^´��l ¢ [�þ^] ��´Bl ¢ ®¯��´Bl ¢ [�þ�]�B`�¤�¤qg Ë3Î õ ËiË3Îóí Ë3ËiÎ í Ë3ËiÎ í ËiË3Îóò Ë3ËiÎ ò�Æbj\§½�` ËiÎ òií ò�Ë3Î ¥ ò¸ËiÎ ò ò¸ËiÎ ò Ë � Î É Ë � Î É®¬nq�¾¦�c°dkä ò¸Î í ËÇí¸Î õ Ë É Î ò Ë É ÎqË Ë È Îóò Ë È ÎqË����nq¦�l¬� ò¸Î í òiþ¸Î � ò3í�Î É ò3í�Î È ò È Î õ ò3ò�Î íï°�Ñ�¸`�� Ë3Î õ Ë � Îóþ Ë�þ�Î ò Ë�þ�Î õ ËiË3Î õ Ë õ ÎD�c�`�ejg3�¾� Ë3Î õ Ë É Îóí Ë3ËiÎ � Ë3ËiÎ þ Ë õ Îóò �¸Îóþ

#�;�6�Û.�Ì����hG¡ ï°b³¦.�hgÆ\§�Ñ�aÅ*\���\À��\i��²³`¨c�`�\3� 0¬n���´â`Ç����`�b���\�±3`�dë�.gi� ¢ �³¤q¤�¦�ð*b³g�¿�¤q`­�¸±3`6®°¤q±3gi�En��E²³p¶d

�E²Ð\§bß�B¦�©âï6ï£ð n�bé�E²³` õ Î É>C�õ Î �I�Ñ\§b³±i`¶g§�údE��\�¤qnqb¥±À��\3���Eg3�Ñd¯�.g3� È�� � ��Å"! Î ¢ g3�(��´o��l ¢ ÏBdE\��E�³�Ñ\§�En�g3b�¸g�`�d�b³gi�¬g������³�°\3d°�^�¥n���½¸¤�·�Î#� bÐ��g3�¾ehgi��\��Enqb¥±C��\i��²¥`*½¸b¥g§¿�¤�`��¸±i`¯¿�n¹�¸`�bjdo�¾²³`6¿�nqbj��g§¿1¿�²³`��E`¨��´Bl ¢ ¦�j\idk`��C\�¤q±ig3�En��E²³p�d�\§�¾`*df�³ej`��En�g3�o�¾g5�B¦�©âï6ï£ð5Î���bÊ�¾²³`£��\3df`¬g�� �åäÄ�ÇÌæç� Ïh��´o��l ¢ e¥�Eg�ä¸n¹�¸`�d�nqbÐ���E`�\idk`��ej`��k�.gi�Ep¶\�bj��`¬�.gi�*\�¤q¤ØdE��\�¤qnqb¥±æ��\i���Egi��d�dk�¾�j�¸n�`���Î

��´Bl ¢ dE��²³`����³¤qn�b³±6g§���E²¥` �å  ¢¤£�� �E��\i��`*`�ý�²³n��³nq�Ñdânqb��E`��¾`�dk�¾nqb³±6�j`�²j\�ä�nqgi��Îâºßn��E²³gi�³���Ç\3��²³`¬½�b³g�¿�¤q¦`��¸±i`�ϯ�^´ël ¢ ¦��j\idk`��1\§¤q±ig3�¾nq�E²¥p¶dÊ��gß\Õä�`��E·éejg�g3�Fhfg3�ùg§�ædE��²³`��¸�³¤�nqb³±ê�E²³`�g����Ç\3dkn�g3bj\�¤6�³�³��df��d¶g§�dk`­�^�³`Çb¸�¾n�\§¤G�¾`�\3�¥dÿ�¾²j\§�6��g3pCn�bj\§�¾`¯�¾²³`Òej`��f�.g3�¾p¶\§bj��`¯pÄ`��E�¾n���d��.g3�°�E²³n¹dÿ�¾��\3��`�ΰŬ�³�En�b³±¶\(dk`����³`�b��En¹\§¤�E`­\3�Ê�³�¥��dk�ÇÏh��´Bl ¢ �Ñ\§�¾`�¤q·(��²³g�g�df`�dë�¾g5df`��Eä�n���`��¾`����³`�dk�Ñd�nqbC¤�g3±3n¹��\§¤�¤q·m\3dE��`�bj�¸n�b³±Ògi���¸`���f¸��·5�E²³`°�En�pC`�E²¥`6�³\§�Ñ\æ�¾��\�bjd �.`��°\�bj�¶��¤q`­\§b��³eCg�ä�`��E²¥`�\3�³d���g3pÄe³¤q`��¾`o�.g3��gib³`6�E`�\i�Ê�E`����³`�df��Ï��E²³`*�¾`�\3��^�¿��En��E`6²³`�\i�²j\idë�Egi��\��E`��ÊeÐ\3dk���¾²³`�Ój��df��dk`­���Egi�ëg����E²³`£b³`�ý��odf`����³`�b��En�\�¤³�E`­\3�Ê�¾`��^�¥`�dk�ÇÎ�lo²��jd�Ï��E²¥`6dE��²³`��¸�¥¤q`���¿�n�¤q¤e³�¾`��¸n�����\§¤�pCg�df��\m�.�³¤�¤j�Eg3�Ñ\§�¾nqg3bÂg§�&ejg�dkn��En�g3b³n�b³±(�¸`�¤¹\­·5�.g3���E²j\��¬�¾`����³`�dk�ÇÎ�®*dB�E²³`¨���³`��³`£g§�&eh`Çbj�¸nqb¥±�E`­�^�³`­dk��d6±3�¾g§¿°d�Ïo�E²¥`¶dE��²³`��¸�¥¤q`��¨¿�nq¤q¤\§¤�pCg�df�5\§¤�¿�\�·¥d¯�j`Â\§�³¤�`À�¾g�¤qg���\��E`Â\§b¥g3�E²¥`��5�E`����³`�df�Ò¿�²³gÆdk`�³\���\a�Ç\§bÕ�j`(ehgÆdkn��Enqgib³`��Ìg�ä�`��6pCgi�E`(���³n���½�¤q·�Î ¢ nq±3�¥�E`Äí¸ÎqË � \�df²³g�¿°d¯�E²Ð\§�Ê�^´ël ¢ \§bj�Õ®6��´Bl ¢ [�þ�]dE\��E�³�Ñ\§�¾`a�j`��.g3�¾`�\�¤q¤�g3�¾²³`��(\�¤q±3gi�En��E²³p¶d�Ïën�bj��¤��j�¸nqb¥± ¢ � ¢ �jÎo��n�bj��`¶�E²³`¶�³�¥��dk�Ñdæg��¨dk`­�^�³`Çb¸�¾n�\§¤��E`�\i��E`­�^�³`­dk��d°nqb �å �¢¤£ � \��E�En�ä�`Òn�b�¤qg3±in���\�¤q¤�·a\idE��`Çbj�¸nqb¥±Àgi���¸`Ç��Ï��¾²³`(dk`�`ǽ¸¦.�E`����j��nqb¥±C\�¤q±3gi�En��E²³p¶d°\§bÐ�I�¾²³`��\i��²³`Ǧ�df`�bjdkn��En�ä�`a��´Bl ¢ \�¤q±3gi�En��E²³p¶d5df`��Eä�n���`C�E`����³`�df��dÒn�b ¢ � ¢ �¼g3����`��a[��.g3�(�E²³`å�¸�³�Ñ\§�En�g3b g§�6�¾²³`�³�³�Ñdk��]�Î

lo²³`�ej`��k�.gi�Ep¶\�bj��`Bg§�Ð�E²³`\§±3`Ǧ�df`�bjdkn��En�ä�`¬��´Bl ¢ \§¤�±3gi�Enq�¾²³p¶d�[.n�Î `ÆÎqÏ�®¯��´Bl ¢ [�þ^]�\�bj�5®¯��´o��l ¢ [�þ^]¾]\§�¾`Õ\�bj\§¤�· Ç`�� n�bñdf`����¾nqg3b1í¸Îóò¸Î�Ë3Ϭ�¥�³�an��Cn�dC¿ogi�E�¾²ñb³g3�¾nqb³±é�¾²j\§�Â�E²³`ê\§±inqb³±é��\3���¾g3�Â��\§b1nqpCe³�¾g�ä�`ej`��k�.gi�Ep¶\�bj��`¨\3d°¿o`�¤�¤�\3d*df��\§�¾äi\§�En�g3b��¾`�dkn¹dk��\�bj��`¨nqb�dfg3pC`¨��\idk`�d�Î1���£�¸g�`�d¬�¾²³n�d��¸·¶p¶\�nqb���\�nqb³n�b³±Ò�¾²³`g3�Ñ�¸`��¾nqb³±5g���dk`����³`�b��En¹\§¤��E`����³`�df��d*[�nÃ���E²³`¨d¾��²³`­�¸�³¤q`Ç�o�E`­��`�nqä�`­d»�¾²³`�pÔn�b¶¤qg3±in���\�¤q¤�·C\idE��`�bÐ�¸nqb³±(g3�Ñ�¸`���]�Î

ÖØ�º¹/Á��¸ÜjÞ�� ;³ÛoÖ�Þ����(;�A »FdGÞ�� A÷�½¼�;¸Þ��.ájÜ¿¾lo²³`°\§�jg�ä�`o`Çý¸ej`��¾nqpC`�b���dj¿o`��¾`o�¾`�ej`�\§�¾`��¯�¾g6dk�¾�j�¸·6�E²³`�`�û�`­����dGg§����g3bj��\��E`�bÐ\§�En�g3b(\�bj�5dk`����³`�b��En¹\§¤

dE��²³`����³¤qn�b³±5g§�dk`­�^�³`Çb¸�¾n�\§¤G�¾`����³`�dk�°df�E�¾`�\§p¶d�ά��n�bj��`¨dE��²³`��¸�¥¤qnqb¥±Ên�bj�¸nqä�n����j\§¤�df`��^�¥`�b¸�¾n�\�¤�¿��En��E`�d��Eg�\�¸n¹dk½¼¿�nq�E²¥g3�³�¨¿��Enq�¾`Êe¥�E`��³��û�`Ç�Enqb¥±��¸`�±i��\i�¸`�dÒej`��k�.gi�Ep¶\�bj��`¶[�dk`�`CeÐ\§±3`�í¸Ë§]ÑÏë�¾²³n�d*ej\��E�¾n����³¤¹\§�mdk`��¨g§�`�ý�ej`��En�pC`�b���dB�¸g�`�d�b³g3�°��g3bjdfn��¸`��°df`����³`�b��En�\�¤Gd¾��²³`­�¸�³¤qn�b³±5g§�&¿��En��E`6�E`­�^�³`­dk��d�Î

¢ nq±i�³�E`­d¬í�Î ò3ò C í�Î ò � df²³g�¿ç�¾`�dk�¥¤q��dë�.gi�6©Gª�«¬¦.�j\3df`��a\�bj�À�.�³¤�¤q¦.½¸b³g�¿�¤�`��¸±3`¨d¾��²³`­�¸�³¤qn�b³±(\§¤�±3gi�Enq�¾²³p¶d�jdfnqb³±5�¾²³`¨dk`����³`�b��En¹\§¤Gdf�E�¾`�\§pÔgie³�En�pCn�­\§�En�g3bjd�Î#2ë\i��²¶�j\��E±i��\§e¥²¼�¸n�dfe³¤�\�·¥dëpC`�\�bC�E`­dkejg3bjdf`Ò�¾nqpC`�dâ�.gi��.g3�¥�âä�`��Ñdkn�g3bjdGg§�j`­\3��²5\§¤�±3gi�Enq�¾²³pµ\��B\ÿ�¾��\i��`�d¾��\§¤�nqb³±���\3���¾g3�&\§¤�g3b³±*�¾²³` �E½�b³`�`>��g§�Ð�E²³`dk`���g§�j�¾`�dkejgibjdk`�En�pC`5���³�Eä�`�d�ÎC�B¦�©âï6ï£ðÔp¶\§n�b¸�Ñ\§nqbÐd¬�E²³`(¤qg�¿�`�dk�6pC`�\�b��E`�dfejg3bjdf`C�En�pC`5\�pCg3b³±¶�¾²³`Cdf`�`�½�¦��¾`��¸�j��nqb³±

Page 72: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�

Scheduling AlgorithmÀ0

50

100

150

200

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOKÁ LOOKÁ SSTFÂ VSCAN(0.2) SPTF ASPTF(6) SPCTFÃ ASPCTF(6)Ã

���.�¡Á����I�����h��¡4��� ����� Ï�Ë3Î � í¤3 � ��`����³`�b��En�\�¤â���¾�E`�\�p ®¬¤�±3g3�¾nq�¾²³pÔ´�`��k�.gi�Ep¶\�bj��`

Scheduling AlgorithmÀ0

20

40

60

80

100

120

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

Sat

urat

edÄ

Sat

urat

ed

Sat

urat

edÄ

Sat

urat

edS

atur

ated

Sat

urat

ed

C-LOOKÁ LOOKÁ SSTFÂ VSCAN(0.2)Å SPTFÆ ASPTF(6)Ç SPCTFÃ ASPCTF(6)Ã

���.�9Áâ���I����� hî¡��å �¢¤£�� Ï�Ë3Îóò3í>3 � �Æ`��^�¥`�b¸�¾n�\�¤î�Æ�E�E`­\§p ®¬¤�±3gi�Enq�¾²³p ´â`Ç�k�.g3�¾p¶\§bÐ��`

Page 73: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ õ

Scheduling AlgorithmÀ0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOKÁ LOOKÁ SSTFÂ VSCAN(0.2) SPTF ASPTF(6) SPCTFÃ ASPCTF(6)Ã

���.�9Áâ���������ÉÈG¡%Ã�ÄÆÅ Ç È%ÊÌË Ï¥ò¸Îóí¤3 � ��`­�^�³`Çb¸�¾n�\§¤����E�¾`�\§p ®¬¤q±ig3�En��E²³pì´â`��f�.g3�¾p¶\§bj��`

Scheduling AlgorithmÀ0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOKÁ LOOKÁ SSTFÂ VSCAN(0.2)Å SPTFÆ ASPTF(6)Ç SPCTFÃ ASPCTF(6)Ã

���.�9Áâ���������j��¡%�åäÄ�Çæç� ÏGò¸Îóí¤3 � ��`����³`�b��En�\�¤â���¾�E`�\�p ®¬¤�±3g3�¾nq�¾²³pÔ´�`��k�.gi�Ep¶\�bj��`

Page 74: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ¸Ë

Scheduling AlgorithmÀ0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOKÁ LOOKÁ SSTFÂ VSCAN(0.2) SPTF ASPTF(6) SPCTFÃ ASPCTF(6)Ã

���.�¡Á����I������ÂG¡�� Å+� � Å Ï�ËiÎ õ 3 � ��`����³`�b��En�\�¤G���E�¾`�\§p ®°¤q±3gi�En��E²³p ´�`��k�.gi�Ep¶\�bj��`

Scheduling AlgorithmÀ0

20

40

60

80

100

120

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

Sat

urat

edS

atur

ated

Sat

urat

ed

C-LOOKÁ LOOKÁ SSTFÂ VSCAN(0.2)Å SPTFÆ ASPTF(6)Ç SPCTFÃ ASPCTF(6)Ã

���.�9Áâ���I�����9â�¡�È1� � ��Å1! ÏjË3Î õ 3 � �Æ`��^�¥`�b¸�¾n�\�¤â���¾�E`�\�p ®¬¤q±ig3�¾nq�E²¥pÔ´â`Ç�k�.g3�¾p¶\§bÐ��`

Page 75: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ3ò

\§¤�±3gi�Enq�¾²³p¶dÿ�.gi�¨\§¤q¤&�E��\i��`�d*`�ý¥��`�e³� ��������� ÎÄ®*d*nqb¼e³�E`Çä¸n�g3�jd¬`Çý¸ej`��¾nqpC`�b���d�Ï�\�¤q¤�gi�E²³`Ç�Òdf`�`�½�¦��¾`��¸�j��nqb³±\§¤�±3gi�Enq�¾²³p¶dogi�³�Eej`��f�.g3�Ep �B¦�©âï6ï*ðç�.gi���E²³n¹dÿ�¾��\i��`�Î ¢ g3�°`�ý¥\§pCe³¤�`�ϳ�³��l ¢ ²j\id*\CË C ò^ÍÔ¤�g�¿o`���pC`�\§b�E`­dkejg3bjdf`Ò�¾nqpC`°�E²j\�bÌ�B¦�©âï6ï*ðü\��.�E`���`Çbj\§�³¤�nqb³±(��g3bj��\��E`�bÐ\§�En�g3bÂg§�»dk`����³`�b��En¹\§¤�¿��¾nq�¾`¯�¾`����³`�dk�Ñd�Î

¢ g3� Ã�ÄÆÅ�ÇÉÈ�ÊÌË Ï �åäÄ�Çæç� Ï � Å+� � Å Ï�\§bj� È1� � ��Å1! Ï��¾²³`Ädk`����³`�b��En¹\§¤Bd¾��²³`­�¸�³¤qn�b³±¶g3e³�¾nqpCn��\§�¾nqgibjd*\­û�`�����E²¥`Cej`��k�.gi�Ep¶\�bj��`5g§�£©âï6ï£ð5Ïë�³�^l ¢ Ï�\�bj�Ì�Ò�³��®£«Ò[ õ Î ò^]°n�bé\a�¸nÃû�`��E`�b��*��\3df²³nqgibÕ�E²j\�bß�B¦�©âï6ï£ð5ή �¸n¹dE���jd¾dkn�g3bùg§�5�¾²³`�nqpÄe³¤q`�p(`�b���\��Enqgib �¸`���\�nq¤¹dæ�.g3�Âdk`­�^�³`Çb¸�¾n�\§¤£dE��²³`����³¤qn�b³±Õg§�m�E²³`­dk`¼\§¤�±3gi�Enq�¾²³p¶ddk²¥g3�³¤¹� ²¥`�¤qeÕ`Çý¸e³¤¹\§n�bÕ�E²³n¹dÒ�j`�²j\�ä¸n�g3�ÇÎIºßn��E²³gi�³�5�E²¥`adf`����³`�b��En�\�¤�dE��²³`��¸�³¤�nqb³±Âg3e³�¾nqpCn��\§�¾nqgibGÏG�E²³`�df`�E²¥�E`�`Ä\§¤�±3g3�¾nq�¾²³p¶dÿ�.�¾`��^�¥`�b¸�¾¤q·ÂdE��²³`����³¤q`(df�E�E`­\§p¶d¬g��£dk`����³`�b��En¹\§¤��¾`����³`�dk�Ñd*nqb�¤qgi±3n¹��\§¤�¤q·���`�dE��`Çbj�¸nqb¥±g3�Ñ�¸`��ËÊ \¼²³nq±i²³¤q·é�³bj��`�dkn���\§�¥¤q`¶�j`�²j\�ä¸n�g3�5�.g3�¶��n�dk½¥d5¿�nq�E² e³�E`��.`�����²³nqb¥±¼��\3��²³`�d�Î ©âï6ï£ð \§¤�¿�\�·¥ddk`Ç�Eä�n���`�dÒ�¾`����³`�dk�Ñdæn�bߤqgi±3n��Ç\§¤q¤�·é�¸`�d¾��`�bj��nqb³±¼g3�Ñ�¸`��¶�¸�¥�Enqb¥±Ì�¾²³`!���¸`­dE��`�bÐ�¸nqb³± �Ie¥²j\3df`Ìg��6nq�ÑdCdE��\�b��·¥��¤q`ÆÎßŬ�³�¾nqb³±Õ�¾²³` �Ñ�¸`�d¾��`�bj�¸n�b³±��¼e³²j\3df`�g§�¨�Ò�³��®£«Ò[ õ Î ò^]ÑÏonq�(�E�¾`�\§�ÑdC\Õdf`��^�¥`�b¸�¾n�\�¤°dk�E�¾`�\§p �¾²³`dE\�pC`¨\3d6©âï6ï£ðü\3d*¤qgib³±C\id*b³g¶\3�¥�¸nq�¾nqg3bÐ\§¤&dk�E�¾`�\§pô�E`����³`�df��d°\§�¾�Enqä�`6gibj��`5nq�°²j\id¬�j`�±3�³b¼df`��Eä�n���nqb³±�E²¥`6dk�¾�E`�\�p�Îë�³�^l ¢ �j`�²Ð\­ä�`­dë�E²¥`6dE\�pC`6\3do�¨�³��®*«Ò[ õ Î ò�]�nÃ��nq��\�e³e³�¾g�\3��²³`�dë�.�¾g3pÔ¤�g3±in���\�¤q¤q· �Ñ\§�jg�ä�`>��E²¥`Òdf�E�¾`�\§p�Î

lo²³`��E²¥�E`�`å\§¤q±ig3�¾nq�E²¥p¶dÊ��nèû�`��(nqbö²¥g§¿ �¾²³`�·ö²Ð\§bj�¸¤�`�df�E�E`­\§p �¾`����³`�dk�Ñdæ�¾²j\§��\§�E�¾nqä�`å\­�.�E`Ç�Ê�¾²³`dk`Ç�Eä�n���`Bg§�Ð�E²³`dk�E�¾`�\§pµ²j\idâ�j`�±3�¥bGÎ�©âï6ï£ð n�±3b³gi�E`�dG�E²¥`o�E`­�^�³`­dk��d��¥b¸�¾nq¤�nq�Ñdîb¥`�ý¸����\idE��`Çbj�¸nqb¥±��¬e³²Ð\3dk`ÆÎ�Ò�³��®£«Ò[ õ Î ò^]�²j\�bj�¸¤q`­d¬�E²³`5b¥`�¿µ�E`����³`�df��d6[�nqb�¤�g3±in���\�¤q¤q·�\3dE��`�bj�¸n�b³±Cg3�Ñ�¸`���]°\­�.�¾`��*nq�£��gipCe³¤q`Ç�E`�do�¾²³`e³�¾`�ä¸n�g3�jd�dk�¾�E`�\�p �¾`��^�¥`�dk�Ñdâ\idâ¤qgib³±6\3d��E²³`��¾`�\��E`�b Y �B\§b�·6�E`����³`�df��dGnqb¨�E²³`�¤�g3±3n¹��\§¤¥dkeÐ\3��`Ghf�jdf�%�¾�j`�¤qg�¿���E²¥`6dk�¾�E`�\�p [�n�Î `�Î�Ï3¿�nq�¾²³nqb¶\ õ Î ò¯�.�Ñ\3���¾nqg3bÄg§�&�E²³`*¤�g3±in���\�¤GdkeÐ\3��`3]ÑÎo�³��l ¢ \§¤�pCg�df��\§¤q¿\�·³do²j\�bj�¸¤�`�dë�¾²³`b³`�¿ù�E`­�^�³`­dk��don�pCpC`���nq\��E`�¤�·5\��.�E`��°df`��Eä�n���n�b³±Ò�¾²³`6e³�E`Çä¸n�g3�jd�df�E�E`­\§pÔ�¾`��^�¥`�dk�Ñd�Î

lo²³`��¾`��.g3�¾`�Ïh�³�^l ¢ ¿�n��E²¶df`����³`�b��En�\�¤�dE��²³`��¸�³¤�nqb³±mdk`��¾ä¸n¹��`�d�pCgÆdk��dk`����³`�b��En¹\§¤Ødk�E�¾`�\§p�d»n�bC¤qgi±3n¹��\§¤�¤q·\3d¾��`�bj��nqb³±¶g3�Ñ�¸`��Çί�Ò�¥��®*«Ò[ õ Î ò�]�¿�nq�¾²¼dk`����³`�b��En¹\§¤&dE��²³`��¸�³¤�nqb³±��¸g�`�d6dkg¼[����³�En�b³±Cnq�Ñd ���¸`�d¾��`�bj��nqb³± �e³²j\idk`3]m\3d5¤qgib³±¼\3d5�E²¥`��E`Â\§�¾`�b Y �(\§b�·Õ�E`����³`�df��dÒn�b÷�¾²³`¶¤qgi±3n��Ç\§¤°dkeÐ\3��`�hf�jdf�7�¾�h`Ǥqg�¿��I�¾²³`Âdk�¾�E`�\�p�Îï°�E²³`Ç�E¿�n�df`�Ï�nq��dk`Ç�Eä�n���`�d��¾²³g�df`*�E`����³`�df��dBnqbjdf�E`�\i�æg��&��g3b��En�b¸�³n�b³±¯�.gi�E¿\§���Ä\§¤qgib³±5�E²¥`*df�E�E`­\§p�Î&©âï¯ï£ð¿�nq�¾²�df`��^�¥`�b¸�¾n�\�¤GdE��²³`����³¤qn�b³±³Ï³giba�E²¥`¯gi�E²³`Ç�¬²j\�bj��Ï�dk`��¾ä¸n¹��`�dMhf�jdf�¬�¾²³`¯ÓÐ��dk�°�E`­�^�³`­dk��nqbÂ\(dk`����³`�b��En¹\§¤¿��En��E`�[.g3�¨�E`�\i�h]¨dk�¾�E`�\�p �¸�¥�Enqb¥±anq�Ñd �Ñ�¸`�dE��`�bj�¸n�b³±��ae³²Ð\3dk`ÆÏ��E`��¾�³�Eb³n�b³±a�¾g¼dk`��¾ä¸n¹��`(�E²³`C�¾`�dk�¨g§�°�¾²³`dk�¾�E`�\�pô�¸�³�En�b³±¶\(dk�³�Ðdk`����³`�b�� �Ñ\3d¾��`�bj�¸n�b³±��(e³²j\3df`�Î*lo²��jd�ÏG\§¤�¤G�E²³�¾`�`5\�¤q±3gi�En��E²³p¶do�j`�b¥`�Ój�¬�.�¾g3pôdk`�¦���³`�b��En�\�¤³d¾��²¥`��¸�³¤�nqb³±*gie³�En�pCn�­\§�En�g3bjd�Ï3�³�³��©âï6ï£ðñ\§bÐ�æ�Ò�¥��®*«Ò[ õ Î ò�]�dk�¾nq¤q¤Ðdk�¸û�`����.�Egipüb³g3b¥¦�gie³�En�p¶\§¤dk`Ç�Eä�n���n�b³±¶g§�£dk`­�^�³`Çb¸�¾n�\§¤»dk�E�¾`�\§p�d�殬¤��E`��¾bj\§�¾`Cdf`��^�¥`�b¸�¾n�\�¤Bdk�¾�E`�\�p gie³�En�pCn��\��En�g3bjdÿ�.gi�5©âï6ï£ð \§bj��Ò�³��®£«Ò[ õ Î ò^]�p¶\�·¨\�ä�g3n¹�æ�¾²³n�dBej\§�¾�En����³¤�\��ëe¥nq�k��\�¤q¤�Ï3�³�³�B�E²¥`*ejg3�E`Çb¸�¾n�\§¤j�j`�b³`�Ój��d�g§�&\��³±3pÄ`�b¸�¾nqb³±údk�j��²dE��²³`����³¤qn�b³±C\�¤q±ig3�En��E²³p�d¬\��E`5�³bj��¤q`�\��¬¿�²³`ÇbÕ�B¦�©âï6ï£ðÌÊ \§b�`�ý��E�¾`�pC`�¤�·(dknqpÄe³¤q`¨\§¤�±3gi�Enq�¾²³p �Eg¶nqpĦe³¤�`�pC`�b��ÍÊ \§¤q�¾`�\3��·C`�ý�²³nq�³n���dB�E²³`¨�¸`�dfnq�¾`��Ê�j`�²j\�ä�nqg3�ÇÎ

©�g�g3½�nqb³±ê\§�¨�E²³`(�.�³¤q¤�¦�½�b³g�¿�¤q`���±3`Ä\§¤q±ig3�¾nq�E²¥p¶d�ÏB��´o��l ¢ \�bj�Õ®¯�^´��l ¢ [�þ^]6gi�³�Eej`��f�.g3�¾p ��´Bl ¢\§bÐ�a®¯��´Bl ¢ [�þ^]Ñϳ�E`�dfeh`­���En�ä�`�¤q·�ÏÆ\3���¾g�dEd°\§¤�¤�dkn�ýÊ¿�g3�E½�¤qgÆ\3�³d�Î ¢ gi���E²³`¨dk`Ǥq`����¾`��Ê�¾��\3��`Òd¾��\§¤�nqb³±Ò��\i���Egi��d�Ï��\i��²³`¶½�b³g�¿�¤q`���±3`�\�¤q¤�`�ä¸n¹\§�¾`�d5dE\��E�³�Ñ\§�En�g3bùg§�6�¾²³`���n�dk½ df�³�jdk·¥dk�¾`�p �.g3�¶®6��´Bl ¢ [�þ�]5d¾��²³`­�¸�³¤qn�b³±¼g§�È1������Å1! \§bj�À�.gi�6�hgi�E²é��´Bl ¢ \§bj�¼®¯��´Bl ¢ [�þ^]°d¾��²¥`��¸�³¤�nqb³±(g§� �å �¢¤£�� [�df`�`ÒÓj±3�¥�E`�d*í�Î ò È \�bj�¼í¸Î ò � ]ÑÎ��\3��²³`�¦�dk`Çbjdkn��Enqä�`�dE��²³`��¸�³¤�`���d¨\3��²³nq`Çä�`C¤qg�¿o`Ç�5pC`�\§bê�E`�dfehgibjdk`Â�En�pC`�d¯��·Õn�bj���E`­\3dkn�b³±��E²¥`Àgib³¦.�hgÆ\§�Ñ���\i��²³`£²³nq���Ñ\§�E`­d�Î ¢ n�±3�³�¾`Òí�Î ò ¥ e³�¾`�dk`Çb¸�Ñdë�E²¥`¯n�pCe³�¾g§ä�`ÇpÊ`�b���n�bC�E`�\i�À²³n��o�Ñ\§�E`­d¬�¸�¥`*�EgÄ��\3��²³`*½�b³g�¿�¤q¦`��¸±i`�Î�®*�¥�¸nqb³±Ä��\i��²³`6½�b³g�¿�¤q`���±3`Ò�¾gC\�bÌ��´Bl ¢ ¦.�j\idk`���\�¤q±3gi�En��E²³p nqpÄe³�Eg�ä�`�dB�E²³`¨�E`�\i�À²³n�����\§�¾nqgC��·�³e¶�EgÄí õ Íü�.g3���E²¥`Òdf`�¤q`­���E`��(�E��\i��`¨dE��\�¤qn�b³±Ò��\3���¾g3�Ñd�Î

lo²³` �¾`�p¶\�nqb³n�b³±ü\�bj\§¤�·³dfn�dßnqb �E²³n¹d df`����¾nqg3bÔ�.g����Ðdk`�dßg3b �B¦�©âï6ï£ð5ÏI�³�^l ¢ ÏI�^´��l ¢ ϶\§bj�®¯��´o��l ¢ [�þ^]Ñϸ\id��E`�e³�¾`�dk`Çb¸�Ñ\§�En�ä�`�d�g§�Ø�E²³`°df`�`�½�¦��¾`��¸�j��nqb³±6\�bj�Ê��´Bl ¢ ¦.�j\3df`��Cd¾��²³`­�¸�³¤qn�b³±£\§¤q±ig3�¾nq�E²¥p¶d�΢ g3�6�.g3�³�5g��°�E²³`¶dfnqý¼�E�Ñ\3��`�d�Ï���gibj��\��E`�bj\��En�g3bég§�£df`��^�¥`�b¸�¾n�\�¤ë¿��¾nq�¾`Ê�¾`��^�¥`�dk�Ñd¯nqpÄe³�Eg�ä�`�d¬�¾²³`(eh`Ç�k�.g3�¾¦p¶\�bj��`5g§�²³g�df�E¦.�j\3df`��édE��²³`��¸�¥¤qnqb¥±³Î(lo²³`CpC`­\§b��E`­dkejg3bjdf`C�En�pC`�do�.g3� ��������� Ï �¡ �¢¤£�� Ï Ã�ÄÆÅ�ÇÉÈ�ÊÌË Ï�\§bj�

Page 76: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ È

CelloÎ SnakeÏ Air-Rsv Sci-TS OrderÐ ReportÑDisk Request TraceÒ

0.0

0.1

0.2

0.3

0.4

0.5

Rea

d H

it R

atio

ÓCache-Sens..CW.CW.CR.CW.SSR

[�\^]���´Bl ¢ \§bj����´o��l ¢ c�`�\i� 0¬n���c°\§�En�g�d

CelloÎ SnakeÏ Air-Rsv Sci-TS OrderÐ ReportÑDisk Request TraceÒ

0.0

0.1

0.2

0.3

0.4

0.5

Rea

d H

it R

atio

ÓCache-Sens..CW.CW.CR.CW.SSR

[���]®¯��´Bl ¢ [�þ^]�\�bj�a®¯�^´��l ¢ [�þ^]c�`�\3� 0¬n���c°\§�En�g�d

�����9Á����I��� � �G¡ ��pCe¥�Eg�ä�`�p(`�b¸�¨nqbùc�`�\3�!0°nq�¶c°\§�¾nqg�dCg�� ¢ �³¤�¤q¦�ð*b³g�¿�¤q`��¸±i`Õ����²³`��¸�³¤�nqb³±ê®¬¤�±3g3¦�¾nq�¾²³p¶do���³`6�Eg¶��\3��²³`¨ðúb¥g§¿�¤�`��¸±i`

Page 77: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ É

�åäÄ�ÇÌæç� �¸�¾g3e���· � C Ë õ ÍÄÏ�Ë�ò C ËÇþ^ÍÄÏ É ÍCÏ�\§bÐ� ¥C�È3È ÍCÏ��E`�dfeh`­���En�ä�`�¤q·�Î��Bg3bÐ��\§�¾`�bj\§�¾nqgibÌg���dk`����³`�b��En¹\§¤¿��En��E`6�E`­�^�³`­dk��dogib³¤q·Äp¶\§�¾±3nqbÐ\§¤q¤�·(\­û�`����Ñdÿ�¾²³`6pC`�\�bC�E`�dfejg3bjdf`Ò�En�pC`�dâ�.g3� � Å�� � Å \�bj� È�� � ��Å"! Î

¢ g3��\§¤�¤³�E�Ñ\3��`�d�`�ý³��`�e³� �å  ¢¤£�� ϳdf`����³`�b��En�\�¤³df�E�¾`�\§pügie³�En�pCn��\��En�g3bjd��.g3�B�E`­\3�Ò�E`­�^�³`­dk��d�g3b³¤�·5²j\�ä�`°\dkn�±3b³nÃÓ���\�b¸�BnqpÄej\3����g3bÄ�E²³`6�³��l ¢ \�¤q±ig3�En��E²³p [.nè�Ø\§�\§¤�¤�]�Î&®*�³�¸n�b³±6`�nq�¾²³`��B��g3bj��\��E`�bÐ\§�En�g3bCgi��dk`����³`�b³¦�En¹\§¤�dE��²³`����³¤qn�b³±Òg��&dk`����³`�b��En¹\§¤j�E`�\i�³dë�¾gÊ�³�^l ¢ Îè�Bº �¸`­���E`�\idk`�dBpC`�\�bÊ�¾`�dkejg3bÐdk`6�En�pC`�dâ��· � ÍÄÏ È þ^ÍÄÏÈ Ë C�È�É ÍÄϬ\�bj�öí�Í �.g3� Ã�ÄÆÅ ÇÉÈ�ÊÌË Ï �åäÄ�Çæç� Ï � Å+� � Å Ï�\§bj� È1� � ��Å1! Ï��¾`�dkej`����Enqä�`Ǥq·�Îêlo²³`aej`��f�.g3�Ep�\§bj��`g§�m�B¦�©âï6ï£ð ¿�\idæb³gi�Ê`Çý¸ej`����¾`��Õ�Egê��²Ð\§b³±i`À¿�n��E² �E²³`Â\3�¥�¸nq�¾nqg3b g§�¨df`����³`�b��En�\�¤�d¾��²³`­�¸�³¤qn�b³±�g3e¥�Enq¦pCn��\§�¾nqg3bÐdÿ[�dkn�bj��`*n���\§¤��E`�\i�¸·ÄdE��²³`��¸�³¤�`�dë�¾`����³`�dk�Ñdën�bC¤qgi±3n��Ç\§¤q¤�·(\3d¾��`�bj�¸n�b³±5g3�Ñ�¸`���]�ϳ�³�³���E²³`6pCn�b³nqpÄ\§¤nqpÄe³�Eg�ä�`�p(`�b���n�bI�^´ël ¢ ¦��j\idk`��Â\§¤�±3g3�¾nq�¾²³pÔej`��k�.gi�Ep¶\�bj��`°¿�\id¬df�³�Ee³�¾n�dfnqb³±¥Î ¢ gi��¿ogi�E½�¤qg�\i�³d4�k��\§�¾�E²³`Ç��³e9�¶�E²³`5�¾`�dkejgibjdk`C�¾nqpC`m���³�¾ä�`�dÒ[�n�Î `�Î�Ï�¿ogi�E½�¤qgÆ\3�³d6g3b¼�E²³`(ä�`��E·Â`��¸±i`Êg��°dE\��E�³�Ñ\§�¾nqg3b�]�Ïâ�¾²³`Ädk`����³`�b³¦�En¹\§¤�df�E�E`­\§pÔgie³�En�pCn��\��En�g3bjdB`�b³²j\�bj��`6ej`��k�.gi�Ep¶\�bj��`6pCg3�¾`6dkn�±3b³nÃÓ���\�b¸�¾¤q·Â[�`�Î�±³ÎqÏGË õ C Ë�í^Í �.g3�*��´o��l ¢dE��²³`����³¤qn�b³±Òg�� �åäÄ�Çæç� \��°\æ�¾��\i��`¨dE��\�¤qnqb¥±Ò��\3���¾g3�°g§� È Î É í^]ÑÎ

¢ g3�B�E²³` �å �¢¤£ � �¾��\i��`�Ï�dk`����³`�b��En¹\§¤¥dk�¾�E`�\�püg3e³�¾nqpCn��\§�¾nqg3bÐdî�.g3�B�E`­\3�5�E`����³`�df��d�e³�Eg�ä�n��¸`°dfnq±ib³nèÓ��Ç\§b��ej`��k�.gi�Ep¶\�bj��`¨nqpCe³�¾g�ä�`�pÊ`Çb¸�Ñd�Î*®£dEdk�¥pCnqb³±Ä�E²³`(d¾��²³`­�¸�³¤q`Ç�*\�¤q�E`­\3�¸·¼��gibj��\��E`�bj\��E`�d£dk`����³`�b��En¹\§¤�¿��¾nq�E`�E`­�^�³`­dk��d�Ï3\i�³�¸n�b³±*��g3bj��\��E`�bÐ\§�En�g3b¨g§�Ødk`����³`�b��En¹\§¤i�E`�\i�³dâ��`����E`­\3dk`­dîpC`­\§b*�¾`�dkejg3bÐdk`��En�pC`�dj�¸·6þ õ C ��õ Í�ή¬¤��E`��¾bj\§�¾`�¤q·�Ï�df`����³`�b��En�\�¤³d¾��²¥`��¸�³¤�nqb³±°g§�Ø�E`�\i�Ò�E`����³`�df��d��¸`����¾`�\3df`�dâpC`�\�bÒ�¾`�dkejg3bÐdk`°�EnqpÄ`�d��¸·¨ò �ÍC�Èiõ Í�.g3�B�¾²³`¬�f¿�gæ�^´ël ¢ ¦��j\idk`��Ä\§¤q±ig3�¾nq�E²¥p¶d�ÎB��nqbj��`*�B¦�©âï6ï£ðµ\§¤q�¾`�\3��·(dE��²³`��¸�³¤�`�d�df`��^�¥`�b¸�¾n�\�¤³�E`����³`�df��dân�b¤qgi±3n¹��\§¤�¤q·Ä\3dE��`�bj�¸n�b³±5g3�Ñ�¸`���ϳ�¾²³`*¤¹\§�E�¾`���g3e¥�EnqpÄn��\��EnqgibC��g�`�dÿb¥g3�£\§¤q�¾`��on���doej`��f�.g3�Ep�\§bj��`ÆÎë�³��l ¢ Îè�Bº`�ý�ej`��En�`�bj��`�d�\ È Íì�¸�¾g3e¶nqb¶pC`�\�bC�E`­dkejg3bjdf`Ò�¾nqpC`*¿�n��E²Âdk`­�^�³`Çb¸�¾n�\§¤�d¾��²³`­�¸�³¤qn�b³±5g§�&�E`­\3�³d�Î

lo²³` �å �¢¤£�� �¾��\i��`5¿�\idú`Çý³\�pCnqb³`­�À�EgÂ�¸`Ç�E`��¾pCnqb³`6�¾²³`5�E`�\idkgibÕ�j`�²³nqbÐ�a�E²³`(p¶\Thfgi�¬ej`��f�.g3�Ep�\§bj��`\3��ä3\�b¸�Ñ\§±i`Õg§�¨�E²¥`Õdf`��^�¥`�b¸�¾n�\�¤*df�E�E`­\§p gie³�En�pCn�­\§�En�g3bjdÒ�.g3�¶�¾²³n�dÊ¿�g3�¾½¸¤�g�\3��Îülo²³`¼�E��\i��`¼��gib¸�Ñ\§nqbÐdg�����\idkn�g3bj\�¤��³�³�Ñdk��d�g§�»b¸�³pÄ`��Egi�jd�dk`����³`�b��En¹\§¤G�¾`�\3�¶�E`����³`�df��d�Î ¢ g3�°`�ý¥\§pCe³¤�`�ϸ�¾²³`*Ój��df� ���¥\­· �5g§�B�¾²³`�E�Ñ\3��`°[���g3b���\�nqb³n�b³±og�ä�`��&Ë�3ò�Ï õiõ3õ �¾`��^�¥`�dk�Ñd�]j²j\idG\ÿ�³�¥��dk�Gg�� È ¥§É ¥ �E`�\i�*�E`����³`�df��dhg���dkn��` ¥ ð6ª�dk`Ç�Eä�n���`����·C\5dfnqb³±i¤q`¨�¸n�df½�Î&lo²³`6�E`����³`�df��d�\��E`*±i�Eg3�¥eh`­�Ànqb��Eg(òií3þ(ð6ªßdk`����³`�b��En¹\§¤�dk�¾�E`�\�p¶d¬[.n�Î `ÆÎqÏ È òÒ�¾`��^�¥`�dk�Ñdej`��Âdk�¾�E`�\�pa]�Îølo²³`��E�Ñ\3��`­� n�b¸�¾`���\��E�En�äi\§¤°�EnqpÄ`�dÊdf²³g�¿ �¾²³`�`�b��Enq�¾`��³�³�Ñdk�C�j`�n�b³±é�E`���`Çnqä�`��énqb hf�jdf�g�ä�`��ÂË � dk`���g3bj�³d�εlo²³`¼dk`­�^�³`Çb¸�¾n�\§¤£dk�¾�E`�\�p gie³�En�pCn��\��En�g3bjdÒgi�³��\�nqbùpCg�df�Êg��Ò�¾²³`�n��Êej`��f�.g3�Ep�\§bj��`\3��ä3\�b¸�Ñ\§±i`ú�.�¾g3p d¾��²³`­�¸�³¤qn�b³±¨dk�j��²(�³�³��df��d�Î ¢ g3���E²³n¹d�ej\§�¾�En����³¤�\��ë�¥�³��df��ϳ\5�B¦�©âï6ï£ð d¾��²¥`��¸�³¤�`���¿�nq�¾²��gibj��\§�¾`�bj\��Enqgib¶g§�»dk`����³`�b��En¹\§¤��¾`�\3�C�¾`��^�¥`�dk�Ñd��¸�Egiejdo�E²³`6b��³p(�h`Ç�ëg����¾`����³`�dk�Ñd�dk`��¾ä¸n¹��`��5�¸·Ä�E²³`6��n�dk½�EgÂË È�É í¶[�n�Î `�Î�ϳþ3í�Í �.`�¿�`����E`����³`�df��d�]�Î

lâ\��³¤q`mí¸Î É ¤�n�dk�Ñdÿ�¾²³`Ò�¾`��¸�j���Enqgib¶nqba�¾²³`6�Egi��\§¤&b¸�³p(�j`��og��B�E`­�^�³`­dk��d6[�df`��Eä�n���`��Ê��·À�¾²³`¨�¸n�df½³d�]����³`�Eg5�¾`����³`�dk�°��g3bj��\��E`�bÐ\§�En�g3bC�.g3�*�B¦�©âï6ï£ðæÏG�³��l ¢ Ïh��´o��l ¢ Ïj\�bj�a®¯�^´��l ¢ [�þ^]ÑÎo®°¤q�E²¥g3�³±i²adfg3pC`£g§��E²¥`¯ej`��Ñ��`�b���\�±3`�don�bj�¸n��Ç\§�E`£¿�²³`��E`¨��gibj��\��E`�bj\��En�g3b¶e³�Eg�ä�n��¸`­do\5eh`Ç�k�.g3�¾p¶\§bÐ��`6\3��ä3\�b¸�Ñ\§±i`�Ïhgi�E²³`Ç��d�\§�¾`�¸`���`�e³�En�ä�`�Î ¢ g3�°`�ý¥\§pCe³¤�`�ϳ�B¦�©âï6ï£ð5Îè�Bº dE��²³`����³¤qn�b³±5g§� �¡äÄ�Çæç� �¸`����E`�\idk`�d�pC`�\�bC�E`�dfejg3bjdf`5�EnqpÄ`�d��· ¥ C ò3ò�Í ��·���gibj��\��E`�bj\��En�b³±¶g3b³¤�· õ Î È í^Í g��°\§¤�¤��E`­�^�³`­dk��d�ÎC�B¦�©âï6ï£ð5Îè�BºµÎè��cü��g3bj��\��E`�bÐ\§�E`­d¯\�b\3�¥�¸nq�¾nqg3bÐ\§¤�ò¸Î �ÍC^È Î É Í �E`����³`�df��d�ϳ�¥�³��g3b³¤�·¶�¸`����E`�\idk`�dopC`­\§bC�¾`�dkejg3bÐdk`Ò�¾nqpC`­d»��·�Ë C ò^ÍÄÎ

��bC�E²³`­dk`°`�ý¸ej`��¾nqpC`Çb¸�Ñd�Ïi��g3bj�Ç\§�E`Çbj\§�¾nqg3bÄg§�»dk`����³`�b��En¹\§¤³�¾`�\3�³dBn�d�dk�³ej`��¾nqg3���Egmdk`����³`�b��En¹\§¤�dE��²³`��¸�¥¤q¦nqb¥±*�j`���\§�Ðdk`°g§�G�¾²³`°�¸`����E`�\idk`�nqb5�¾g3�Ñ\§¤³g�ä�`��¾²³`�\3�5��`�¤�\�·6nqbj���³�E�¾`��5\§�B�E²¥`°�¸n�df½�Î ���Ø\*��n�dk½¨²j\3d.�`��¾g5[�gi���¤�g�dk`5�¾g �`��Eg�]°��gipCp¶\§bÐ��n�b³nq�¾n�\��Enqgib�\�bj�Ì��g3pCe³¤�`��En�g3bÂg§ä�`Ç�E²³`�\i�³d�ÏØdk`����³`�b��En¹\§¤&dE��²³`��¸�³¤�nqb³±(g§��E`�\i��E`­�^�³`­dk��d�e³�Eg�ä�n��¸`�d&dk¤qn�±3²��E¤�·¯�j`��¾�E`���ej`��k�.gi�Ep¶\�bj��`��¾²j\§b(��gibj��\��E`�bj\��En�g3b(g§��df`����³`�b��En�\�¤��E`�\i�æ�¾`����³`�dk�Ñd�Î

ÖØקÙ���Ú&Á�Û��.Ü��IÝ(��Þ�Ùß�ÕÔ¨�¬ÖÖÔ¨á9AEAE;³Ü�ÚØ× Áâ�(Áâ��ÚÚÙ¶�Û¾Ì=ܾ2�ä�`�b�²³g�df�E¦.�j\3df`��Õ��`Çb¸�¾��\§¤�n��`­�adE��²³`����³¤qn�b³±C�Ç\§b¼��\§½�`(\i�¸äi\§b���\�±3`Cg��o�¾²³`(nqb��E`��¾¦��¾`��^�¥`�dk�£��g3bÐ���³�E¦

�E`Çbj��·6\�äi\§n�¤�\§�¥¤q`ë�.�¾g3pø�¸n¹dk½¥dî¿�n��E²5��g3pCp¶\�bj�*���³`��³`Çnqb³±¥Î ¢ nq±3�¥�E`�d�í¸Îóò�� C í¸Î 餃 e³�E`­dk`�b��GpC`�\�b¯�¾`�dkejgibjdk`�En�pC`�d*�.g3�¶�B¦�©âï6ï£ð \§�Cejginqb���d(\§¤qgib³±¼�E²³` �E½�b³`�`>��g§�6`­\3��²ödf`��(g§�6�¾`�dkejg3bÐdk`a�¾nqpC`����³�Eä�`­d�Î lo²³`

Page 78: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ3í

lG��\i��` ����\§¤�` ¢ \i���Egi� �B¦�©âï6ï*ð �³�^l ¢ ��´o��l ¢ ®¯��´o��l ¢ [�þ�]�B`Ǥq¤qg Ë3Î � í Ë3Î í È Ë3Îóí3ò Ë3Î É ¥ Ë3Î É ���bj\§½�` Ë3Îóò3í ò¸Î õ�� ò¸Î õ§É ò¸Î õ � ò¸Î�Ë õ®¬n��E¦�c¬dfä ò¸Îóí õ Î ò�Ë õ Îóò õ õ ÎqËÌ� õ Î�Ë�����n�¦�l¬� ò¸Îóí õ Î È í õ Î È þ õ Î ò � õ Î È3õï¬�Ñ�¸`�� Ë3Î õ õ Î õ Ë õ Î õ ò õ Î õ Ë õ Î õ Ëc�`�ejg3�¾� Ë3Î õ õ Î õ Ë õ Î õ Ë õ Î õ Ë õ Î õ Ë

[�\�]¬�Bgibj��\§�¾`�bj\��Enqgibag�����`����³`�b��En¹\§¤jºÌ�¾nq�¾`�d

lG��\i��` ����\§¤�` ¢ \i���Egi� �B¦�©âï6ï*ð �³�^l ¢ ��´o��l ¢ ®¯��´o��l ¢ [�þ�]�B`Ǥq¤qg Ë3Î � í ò¸Î �ÇÉ ò¸Îóþ õ ò¸Î Èiõ ò¸Î È Ë��bj\§½�` Ë3Îóò3í í¸Î þ É í¸Îóþ3í í¸Î É í í¸Î É í®¬n��E¦�c¬dfä ò¸Îóí È Î ÉÆÈ È Î õ�� ò¸Î �­õ ò¸Î ��È����n�¦�l¬� ò¸Îóí È Î �ÇÉ È Î É�¥ ò¸ÎD�ií ò¸Î � �ï¬�Ñ�¸`�� Ë3Î õ õ Î �­õ È Î � þ õ Î É � õ Î É þc�`�ejg3�¾� Ë3Î õ È Î ¥�� õ Î ��É È Î É ¥ È Îóí3ò

[.��]��Bg3bj�Ç\§�E`Çbj\§�¾nqg3b�g��o�Æ`��^�¥`�b¸�¾n�\�¤Gc�`�\3�³d°\§bÐ��º¼�En��E`�d

#�;�6�Û.�I���ÝÈG¡ ´â`Ç����`�b���\�±3`�c�`��¸�j���¾nqgibÒnqbmlîgi��\�¤³c�`����³`�dk�Ñd»�Æ`��Eä�n���`­�¯���³`o�¾gÒ��`����³`�b��En¹\§¤�c�`��^�¥`�dk��Bgibj��\§�¾`�bj\��Enqgib

Page 79: Aggressive Centralized and Distributed Scheduling ofDisk Requests

þ3þ

Scheduling AlgorithmÞ0

50

100

150

200M

ean

Res

pons

e T

ime

(ms)

No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.SSR C-LOOK.CW.SSR

ãåä½æ9Á¿çéèëêíìïî �ÜðËñÕòôóÝóöõø÷¿ùûúýüéþéÿ������������� �������������������! #"%$�&(')�*',+����-�.������/0��1324��24�5/768":9<;49

Scheduling AlgorithmÞ0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

=No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.SSR C-LOOK.CW.SSR

ãåäÛæ?> ç èëêUì%@�¹Üð8ACB4D�E òô÷ÍùøúGFøþéÿ������H��I���� �J�<�����������?�K�8 #"L$M&(')�*'�+N���-�.���5�?/0�<182O�J24�5/.63":9�;O9

Page 80: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P ü

Scheduling AlgorithmÞ0

10

20

30

40

50

60M

ean

Res

pons

e T

ime

(ms)

=No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.SSR C-LOOK.CW.SSR

ãåäÛæ?> çéè êUì%@RQ ð8S�T:UWVYX3Z�[ ÷4F ú þ ÿ\�����H��I���� �J�<�����M�]���?���� #"%$M&('^�*',+������.�]���?/0�<1324�J24�_/`68"a9�;O9

Scheduling AlgorithmÞ0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

=No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.SSR C-LOOK.CW.SSR

ãåä½æ?>¿çéèëêíìL@íîUðbACc�T%VJd�A ÷RF ú þ ÿ\�e���������� �������������������! #"%$�&(')�*',+����-�.������/0��1324��24�5/768":9<;49

Page 81: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P�f

Scheduling AlgorithmÞ0

10

20

30

40

50M

ean

Res

pons

e T

ime

(ms)

=No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.SSR C-LOOK.CW.SSR

ãåä½æ?>¿çéèëêíìL@?@Üð�g#UMhºòiU ÷Uùøúkjéÿ������������� �������������������8 #"L$M&('^�*',+������.���5�?/0�<1324�J24�5/l68":9<;49

Scheduling AlgorithmÞ0

20

40

60

80

100

120

140

Mea

n R

espo

nse

Tim

e (m

s)

No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.SSR C-LOOK.CW.SSR

ãåäÛæ?> ç èëêUì%@ ÈÜð8X ò�m õnUWo½÷ ùûúkjéÿ������H��I���� �J�<�����������?�K�8 #"L$M&p'^�*',+.���-�.���5�?/0�<182O�J24�5/.63":9�;O9

Page 82: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P�q

Scheduling AlgorithmÞ0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

=No CQCQ = 2ßCQ = 4ßCQ = 16ß

Preseekà Fullá

SPCTF.CW.SSRâ C-LOOK.CW.CRr C-LOOK.CW.CRr

ãåäÛæ?> ç èëêUì%@íêUð8ACB4D�E òô÷ÍùøúGFøþéÿ������H��I���� �J�<�����������?�K�8 #"L$M&(')�*'�+N���-�.���5�?/0�<182O�J24�5/.63":9�;O9

9M�W&4�5/s24t%�J�* #�-9#�����0u�v�24���5/N$��7�����?����$M���?��$���9��_wx24���0$�":��t? #��"%$M�I���5wx2O�59�$y9#���?/�9��_wx24���0$�":��tLt%z79��i&4�_/024t%��M�_��/p�M�5wn24�59<$W9 ú|{}&4��u?�W9<$I~?���I�����5�-�i&pv-�W���O&�v-"%�n�598$�&4���?�J�����-�M���5�?���|���!+x ��*{#' ú���� ú�+O+s�������-��M�K���J�M�J�������ôúG��{}&4���M�J���5"%�4"L�4v!$< }�\9��J$y9,�5����-24�}~?�5�W9}v-"%�n�3$M&4�!�l�5�������59��?����9��I$M"L�.�59����-�3/0":9<;49*�����4�u?v-24�M�5/p #"%$�&� ^�M�59<�J�J;(���?/�'424t%t����-�.������/�wn24�J24�J"L�4v(�H/0�59����M"L~?�5/�"%��9<�5��$M"L���p�ÉúÝùøúGFx�#�5�n�J���`�W�5�4v�����)�����s"%��24�����4��~?�n�5�W/pwn24�J24�|/0�J�O$M&?9!��t:��~?�JtL�5/��#1I�ôú

� t%t����*$�&4��$M�y�����59#�J�s&4"%~O"%$3�M�Jta��$M"L�n�Jt%zl9�"L�."%ta���#~?�J&?�J�s"%�-�!�J�O���J�4$IACB4D�E ò ú�+n�_��$M"L��� þºú ùøúGF./0�J�.�-�4�9�$��W�5$M�59�&4�5 ��K���?�J�5$M�J����$M"L��������9��_wx24���0$�":��t����5��/��M�_wx24�_9�$W9�9<"%v-�4"�uC�����s$Mt%z���2O$M�?�J�����-�M��9|9��5wn24�J�s$M"a��t9M�W&4�5/s24t%"L�4v��5���M�5�-/��M�5wn24�59<$W9N������$M&O��AeB4D�E ò�$��W�-��� ú {}&4��9�"L�`2Ot:��$�"%�-�?9N *�J�M�����J�?�5��$��5/�2�9�"%�Ov���-�?�J��$��J�?�5$M"%�-���5�7�M�5�-/49 ÷����?/ u?v�24��� þ úk¡ûþ�9�&O�� 39�$M&?�5$�$M&4���.�5�5���M�_9��?���?9<��$M"L�.��~?�J&��_�s"%�-��������������Ëú���� ú¢�*��9��i&4�_/024t%"L�4v#�����}ACBOD�E ò�]��$W�W&4�59�$�&4�!���������Ëú���� ú¢+4+s��~e��&?�J�0"L�������C$M&4�#�-$M&4���$M�y�����_9 ú

{}&4�.���59�24tL$W98�����\��tLt#9�"L�p$M�y�����59I"%�?/s":�J�5$M��$M&���$���&O�n9�$��Y~���9��_/£�K�J�0$��W�5t%"%¤��5/�9��i&4�_/024t%���v-�J�4�J�y��tLt%z�?�J�����-�M��9�~e�_9�$} #"L$M&l��/0"a9�;\�����.�]���?/�wn24�J24�#tL�J�4v-$M&7����$< }�Éú^¥}z��]��"%�s$W�5"%�4"L�4v}¦<2?9<$�$� *���-24$W9<$W����/0�"%�Ov.�M�5wn24�59<$W98�?�J�|/0"a9�;U÷�$M&O�79M�W&4�5/024tL�J�3$W��;n�_98�-/0�-���s$W��v-�.�������-�?��24���M�J����z�~?�J$< }���J��$�&4�p§W��2O�M�M���0$y¨�M�_wx24�_9�$7����/�$M&4��§M�O�J�0$y¨©���5wn24�59�$7�5$.�5�-�i&�/0"a9�;U÷, #&4"Lt%���4���59��J���0"L�4v�$M&4�(��~O"%t%"L$<z�$���/0zs�?���."a�J��tLt%z�M�����W/s�J�3�Y���*���-�?�J�5$M�J�?�5$M���ª$M&4�3�M�J�]��"%��/0�J�����R$�&4�3�e���?/0"%�Ov���5wn24�59�$y9 ú�{}&?��$�":9 ÷s��&O�n9�$��Y~���9��_/.9M�W&4�5/0�24tL�J�!�M��$W��"L�?9!�.�����«?���0"L~4"%tL"%$<z.$M�����5�����W���Ov��7�e���?/0"%�OvN���5wn24�59�$y98"���$M&4�7�K���.���5�?/�wn24�J2O��t%�J�4v-$M&p"a9;n�J�4$�9�&4�-�M$ ú

{}&4":9��5t:9��|�J�s�4t:�5"%�?9$�&4��/0"�¬C�J���J�?���#"L�.���H��I����~e��&?�J�0"L����~?�J$< }�J�J��$�&4�3$� *�|9��5wn24�J�s$M"a��tO9�$M���5������O$M"%�l"%¤5�5$M"%�-�?9,�����IACB4D�E ò8���5��/����5wx2O�59�$y9 ú � &4�n9<$M��~?��9<�5/­������I��� ú¢��� ú�+4+x�®9M�W&4�5/s24t%�J�3/s�n�598�4�-$�4�J�_/8$M�������s$M"L�02���t%tLz#�M�J�-�W/0���R$M&4�^ta����v���~424�y9�$W9R����9��_wx24���0$�":��t5���5��/49R$M&���$�/0�-�."%�?�5$M�^$�&4�^�?�J�<�����M�]���?����.�J$��M"a�J9������#$�&4":9�$M�y����� ú�¯��-�i&(9��_wx24���0$�":��tC9<$M�M�_���°���M��"%�n�59*��$#$�&4�I9M�W&4�5/s24t%�J��"L�.t%�-v�":����t%tLz.�-9M�����?/0"%�Ov±�²�³#´�µ5¶�³�·:¸:¹-´i³�º�».¼5½?¾�¿�Àp´iÁkÂK¶KÃYÄk·�µ5Å�Ã�º�ÁGÄkº<³#¶�ÆlÇHÈ�Ã�Ã�º�Æ�·8ÉJÆ5¶WÊRÁkº�»JÂKº8¶WË�¶�ÆJ¸a¹�¶�´iÃ�»`»5´W·H´|Ç<´�ÇYµ5º|ÇH¶�Æ�·Yº<ÆJ·�³3´iÆ-»

´KÇÌ·�È-´i·�¶KÃRÍ�¶K³YÄk·�Äk¶KÆ5³MÎJÄk·�»J¶Jº<³RÆ5¶K·R³HÇYµ5º�»JÈ5Ákº�ºÌÏк�ÇÌ·�ÄkÑKº<ÁkÒ8ËL¶�Ã�»JÄk³�ÉJ³RÊRÄk·�µ�Ç̶KÅ3Å!´WÆ-»}Ó�È5º<È5º�ÄGÆ�Â-Ô

Page 83: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ü5j

���y/0�J� ú�{}&4�J����������� ÷#$M&4��/0"a9�;Õ9�24~?9<z49<$M�J� �-�i&O"%�J�n�59�$M&O�p~e�_9�$.�?�J�<�����M�]���?���p~sz��]���s"%�."¢¤J"¢�4vp$�&4��J�-��"%ta��~4tL�I"%�s$M�J���Y���5wx2O�59�$*���-�?��24���M�J�?�Kz���$#$�&4�|/0":9<;íú

'4���I/0"a9�;O982?9<"%�4v.$�&4�� ^���59��J��;��K���.���5�?/�wx2O�J24�J"L�4v.�K���0u?v-24�W�5$M"L���Ü÷R$M&O���.�5�������59��?����9��7$M"%�l�59�����*$M&4��9�"L��$M�y�����59�/0����� üKÖs¡ Px× #&4���`$�&4�8�]���s"%�724�Ø���-�.������/�wx24��24�#t%�J�Ov�$M&l":9^$< }� ú�{}&4�Jz7/0��������Ù��/4/s"%$M"L���?�5t ùiÖxFøþ × �_��$��J�#�J�?�5~4t%"L�4v7'424t%tª�����.�]���?/7wx2O�J24�J"L�4v ú

Ú3Û�Ü}ÛHÝ Þ!ß3à<à©á*â3ã0ä4å^æ ç7è4é�êRå�ã{}&4":9�9��_��$M"L�����K���s$W��"L�?9^�39�"L�."%ta���R9<�J$����C�J�s�e���M"%�l�J�0$y9?�����.�����M"L�4v3&4�n9<$M��~?��9<�5/`9��i&O�5/024tL�J�W9e���-�$�&4�

ë�*��$M�y�����_9 ú3{}&4�59<����24t%t�9<z49<$M�J��$M�y�����_9b�J����~4tL��$M&O��2?9<�����*$�&4���4���s���59�9��:«?�5 ®&4�Ð9�$!�.�s/s�Jt ÷4 #&4"a�i&9�"L�`2Ot:��$��59!$M&4�l~4":/0"L�M�5�K$M"%�-�?��t^���J�_/0~?���W;�~e��$� *�J�J����&O�n9�$7�5�?/��p/s":9�;ì9�2O~?9�zO9�$��J�ëú � tL$M&4�-24v�&�$�&4���tLv��-�M"%$�&4��9*9�$M2�/0"%�5/�"%�.$�&4":939��_��$M"L�������4$�"%�."L¤J�}������9�2O~?9�zO9�$��J���?�J�����-�M���5�?���I�K�M"%$��J�M"a�º÷s$M&4�I�4���s���59M9<�«?�5 Ø�.�s/0�Jt��5t%tL�� 393$M&4�|�.�5��9<24�M���.�J�s$,�5�����4�4tL":�J�5$M"L���4��9��?�5��"¢uC��?�J�<�����������?�K��l�J$M��":�J9*��9! }�JtLt ú � 9~?��������� ÷0$�&4�3~?��9<�Jt%"L�4�!9��i&O�5/024tL"%�4v|��tLv��-�M"%$�&4��9^�5�M�I�K���.�?�5�M�5/�~?���������!�-/4/0"L�4v79��5wn24�J�s$M"a��t?9��i&O�5/024tL"%�4v���O$M"%�l"%¤5�5$M"%�-�?9,�-�3')�*'�+.�K���.���5�?/0��wx2O�J24�5/7/0":9<;49 ú

íªî�ï è�Ú>�ÛÛä�ð æ�ñ?ò ó}ô æ ä�înõ³Û}ö5Û�ôRî5÷£ø(>ù�ñ èºç'"%v-24�M� þºúG¡ P 9<&4�5 398�?�J�����-�M���5�?���|/4��$y�������3$M&O�`ACú-BxX|û òKB` }�-�M;st%�n�-/p�����su?v�24���5/N #"L$M& ùø÷RF ÷e�É÷

����/ f 2?9<�J�W9 ú3{}&4���s24�7~e���}���)2?9��J�y9b"a9b�Ot%��$�$M�5/(��tL���4v.$�&4� ÿ��H�5�0"a9}2?9�"L�4v���t%��v � 9M����t%� ú#¯����W&p/4�5$W��?��"L�0$|":9!$M&4�l�.�5���p�5�3�`2Ot%$M"L�4t%�|$M�y�����7�M24��9 úp{}&4��ACú-BxX|û òKBN~?�J�?�W&4���5�M;�2�9��59I�W����/0���ü�s24�7~?�J�v����4�J�W�5$M"L��� $M�ì/0�J$��J�M�l"%�4�.$�&4�p9<�5wn24�J�?���(���I���n�J�0$y9 ÷�$M&4���K���.�42O$M��$M"L�.�59 ÷��5�?/�$M&O�p9�tL�J�J��$M"%�l�59�������5���W& §M2?9<�J�W¨7v��J�4���W��$�"%�4v]����$�"%�s"%$<z ú � 98�.�M�_9�24tL$ ÷?$M&4���?�J�<�����M�]���?���I�.��$M�M"a�J9}�-����zp9�"Lv��4"¢uC�J�5�0$�t%z~?�J$< }�J���.�M24��9��2?9�"L�4v`$�&4�|9M�5�.�I���-�0u?v�2O�W��$�"%�-���ôú

'"%v-24�M� þºúG¡ P ��9�&4�5 39$�&4�}�.�_�������59��?�-�?9��#$�"%�.�594������/0":9<;I�M�5wn24�59<$W9R2?9�"L�4vI'^�*',+I�5�?/��R¥#ë8��~?��9<�5/���������Ë÷-�����Ë÷5ý�+4� � ë���jºúGFx�ô÷-����/`+4+s{#'Õú-{}&4�#9<�J�J;s�Y���5/02?�K"%�4v3�5t%v��-�M"L$M&4��9���tL�5����t%z!�-24$M�?�J�<�����M�'^�*',+ ú5'4���R$�&4������2?9��J�� }�-�M;st%�Ð��/í÷�"L$W9��.�_���!���59��?����9��}$�"%�.��":9��5�n�J���Ðj × &4"Lv�&4�J� ú^���H��I�����O�M�5�0"a/0�59$M&O��tL�� *�59�$��.�_��� �M�_9��?���?9<��$M"L�.�59����-�(��t%tI~42O$�$M&O��tL"%v�&s$M�_9�$p� ù���2?9��J�K�. *���M;st%�Ð��/í÷I #&4�J���£+O+s{#'��2O$M�?�J�����-�M��9����H��I���þ~sz ù × ú�'��-�.$M&O��F���2?9��J�(�5�?/��-�Y2�9��J�� }�-�M;st%�Ð��/49 ÷���������ü/s�5���M�_��9��_9$M&O���.�5�5���M�59<�e�-�?9��|$M"L�.�!~sz�F-j × ����/ ü × ÷4�M�59<�e�_��$M"L�n�Jt%z ÷O�����l�?�����5/.$M�7$M&4�|��$M&O�J�!9<�J�J;s�Y���5/02?�K"%�4v��tLv��-�M"%$�&4��9 ú

'"%v-24�M� þºúG¡ P ~79<&4�5 39^$M&4���������M�59<�e�-�?/0"L�4v!�.�5�5�����-�.�4tL�J$M"L���!$�"%�.�59e���-�$�&4�!ACú-BxX|û òKBb$y��9�;O9 ú�'4�-�$M&O":9R�.�J$M��":�ø÷K$M&4��9��J��;0���M�5/s2?��"%�Ov!�5t%v��-�M"L$M&4��9��-24$M�?�J�<��������'^�*',+3~0zI���Ot%z|F × ú^ÿ8�5 *�J�n�J� ÷J$�&4�}ta����v��59<$���W�-��$M"L���p�5�#$M&O��$W��9<;������l�4t%�J$�"%�-�N$�"%�.�I"a9�$�&4��$M"L�.��§M�J�s�5��2O$M"%�Ovn¨.���s/s��������� �]��"%�(�.�J�.�-�Mz(�Y$�&4�înô?ù � >��éè��éäYù è4�ôú�'"Lv�24��� þ úk¡ P �I9�&4�5 39}$M&O�8�.�_���7$W��9<;.�4�-�4�H�K���.�42O$M�3$M"%�l�59}�Y" ú � ú ÷�$M&O�!�.�5�5�`$y��9�;���-�.�4t%��$M"%�-�`$�"%�.�_9�J�O��t%2?/s"%�4v|$M&4�!ta����v��|���4�Ot%":����$M"L�����K���.�42O$M�!$�"%�.�59W�ôú�'4���*$M&4�I����2?9<�J�3���?/ f �Y2?9<�J� }�-�M;st%�Ð��/49 ÷}$M&4���.�_�����4���O�H���-�.�424$���$M"%�l�./0�����?9�~szÚùJFJÖ ùJ¡ × �5�?/ üKÖ ùJj × ÷#���59��?�5��$�"%�n�JtLz ÷ #&O�J���9��J��;0���M�5/s2?��"%�Ov��5t%v��-�M"L$M&4� �M�J�4ta�����_9`'^�*',+ ú8������I���þ��24$��?�J�����-�M��9`$�&4�p��$�&4�J��9<�J�J;s�Y���5/02?�K"%�4v��tLv��-�M"%$�&4��9�~0zëùWÖs¡ × ���-�8$�&4�59<� *����;0tL�n��/O9 ú

'"%v-24�M� þ úk¡ üÙ�4�M�59<�J�s$W9��?�J�����-�M���5�?���(/4�5$W�©���-�`�J�s�?�J�M"L�.�J�s$W9!2?9<"%�4v�$M&4� ñ õ��8mCUôòMZWZ� *����;0tL�n��/Uú¯����W& /4��$y�£�?��"L�0$l":9`$�&4�p�.�5�5� ���Iu?�n��9����?���y��$M�p$��W�-������24�?9 ú�'"%v-24�M� þºúG¡ ü5��9�&4�5 39.$M&O�p�.�5����M�_9��?���?9<��$�"%�.�59���-�3')�*',+����?/�$M&4�|�R¥#ë8��~?��9<�5/���tLv�����"%$�&4��9 ú�'4���#$M&O":9}�.�J$��M"a�ø÷�$M&O��9<�J�J;s�Y���5/02?�K"%�4v��tLv��-�M"%$�&4��98�O�M�s/02?�K� ù þ × ~?�J$M$��J�!�?�J�<�����M�]���?���|$M&?�5��'^�*',+ úª'"%v-24�M� þ úk¡ ü�~�9<&4�5 39$�&4��$M�-$W��t���24�$M"L�.�������|$M&4�7u?t%�l�����l�4�M�59�9�"L�����4�M�s���_9M9 úÙ{}&4��9����J;0���M�_/02?��"L�4v(��t%v-����"%$M&O��9I/0�5�����5��9<�.���-�.�4���59M9<"%���$M"L�.�59!~sz��5�4�4�M�5�s"%���5$M�JtLzpF × ú � tL$M&4�-24v�&�$�&4":9��]�_z�9<�J�J� "L�?9�"Lv��4"¢uC�J���s$ ÷^$�&4�.���5v��4"L$M2?/s�`�5�!$�&4�

Page 84: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ü ù

� � FCFS� � C-LOOK LOOK VSCAN(0.2) � � SSTF

|�1.0 |�

2.0 |�4.0 |�

8.0 |�0

|�100

|�200

|�300

|�400

|�500

Number of Users

Mea

n Re

spon

se T

ime (

ms)

��

� ��

��

��

��

�������������! "��#%$���&(') *��&(+-,%�.&(�0/21435�

6 6 FCFS7 7 C-LOOK 8 8 LOOK 9 9 VSCAN(0.2) : : SSTF

|;1.0< |;

2.0< |;4.0< |;

8.0<|=0

|=500

|=1000|=1500

|=2000

|=2500

|=3000

|=3500

Number of Users

Mea

n Ta

sk C

ompl

etio

n Ti

me (

ms)

>>

>>

??

??

@@

@@

AA

AA

BB

BB

�DCE���������!/F�G&(H!I2,%35+�J4�K'(14,%�L/�1M3N�

O O FCFSP P C-LOOK Q Q LOOK R R VSCAN(0.2) S S SSTF

|�1.0 |�

2.0 |�4.0 |�

8.0 |�0

|�100

|�200

|�300

|�400

|�500

Number of Users

Mea

n N

on-C

ompu

te T

ime (

ms)

T

TT

T

U

UU

U

V

VV

V

W

WW

W

X

XX

X

��YZ�*�!���[�!\],%��^(I2,%35+�$�'_�`/21435�

ãåä½æe> çéè êUìL@baÜð8Aeú�B4UdcºòKB0�*�R¥#ë8��¥#��9��_/ � t%v��-�M"L$M&4�� ��J�����-�M���5�?���

Page 85: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ü5F

FCFS C-LOOKe LOOKe SSTFf VSCAN(0.2)gScheduling Algorithmh

0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

i

�H�x�kj��5�5���#�59<�e�-�?9��\{}"%�.�

FCFS C-LOOKe LOOKe SSTFf VSCAN(0.2)gScheduling Algorithmh

0

50

100

150

200

Appl

icat

ion

Run

Tim

e (s

ec)

l

��~�� � �4�Ot%":����$M"L�����#24�({}"%�l�

ãåä½æ?>¿çéè êUìL@nmíð ñ õ��8mCU òMZWZK���R¥#ë8�H¥#�-9��5/ � tLv��-�M"%$�&4�� �������������������

Page 86: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ü5¡

"%�l�4�M�5�n�J�7�J�n$�9�&4�-24t:/�"L�?�����5��9<�� #"%$M&�$M&O�.�4�M�s�K�59M9<"%�4v(�e�5 *�J�I���3$M&O�`&4�Ð9�$\9�zO9�$M���ëú.�8��$M&O�.ë�*� }�-�M;O9�$y��$M"L����$M�y�����5/U÷�$M&4� ñ õ��8mCUôòMZWZ# *���M;st%�Ð��/�"a9!��$It%�_��9�$��?����$M":�5t%tLz©�* ]o8��~?��24��/qpR$�&4���4�M�s�K�59M9<���9��?�J��/49!���O�4�M�5�s"%���5$M�JtLzëùJj × ���)"%$W93$M"%�l�!"%�($M&4��"a/0t%�It%�n�-�ÜúI'4����������9<$M�J��&4�n9<$I9�zO9�$��J�ë÷ ñ õ��8mCU ò�ZWZ���-24t:/�~?�5�K���.�Lrts��3�Y~?�-24�?/Ü÷^�M�59<24t%$�"%�4v("%���� *����;0tL�n��/��72?�W&p�.�����.9<�J�?9�"L$M"L�n��$M��/0"a9�;ì9�24~?9<z49<$M�J��?�J�����-�M���5�?��� ú

íªî�ï è.u>�ÛÛä�ð æwv äx�5ïÚãR>�Û�Û)y(ðô�v(ÛÛè.u æ è'"%v-24�M� þ úk¡ f ��9<&4�5 39�.�_�������59��?�-�?9��.$�"%�.�_9����-��+s �{#'��~?��9<�5/�9M�W&4�5/s24t%"L�4v.����ACú�BnX|û òiBºú7{}&4�

��24tLt%��;0�4�5 #tL�5/0v�����t%v-����"%$M&O��9}&?�J�n� ü�Ö qx× t%�-�4v����#�.�5���l�M�59<�e�-�?9��|$M"L�.�59,$�&?�������H��I���������3�5t%tR~42O$$M&O� ùK�Y2�9��J�3 }�-�M;st%�n�-/íú*ÿ8�5 }�J�n�J� ÷n$M&4"a9}":9}�4�-$8����«?�5��$��5/`"L�N��"%$M&O�J�}$�&4�I�.�5���l$W��9<;(�����.�Ot%�J$�"%���7$M"L�.����3$M&O��l�5���.�O���4�������l�424$M��$M"%�l����9��J�!u?v-24�M�59 þºúG¡ f ~p����/ þºúG¡ f ���ôú

'"%v-24�M� þ úk¡ q ��9�&4�5 39I$M&4���.�_�������59��?�-�?9��7$M"L�.�59,�����!��24tLt%��;0�O�� #tL�5/0v-��9M�W&4�5/s24t%"L�4v`�5�#$�&4� ñ õ���VmCU ò�ZWZ# }�-�M;st%�n�-/íú���������� &���9!�.F × tL�� *�J�3�.�5�������59��?����9��7$M"%�l�!$M&?�5�£+x ,{#' �5�?/ � +s �{#'}� P � ú{}&4�(�J�-�i&4���H9<�J�?9�"L$M"L�n�.�5t%v��-�M"L$M&4��9I�4�M�5�s":/0�l$M&4�. *���y9�$7�e������������������� ÷ #"L$M&��.�5�5�����59��?�-�?9��($M"%�l�59ù qn× &4"%v-&4�J��$M&�����������I�!� ���?/`�-�4t%z\F × tL�� *�J�^$�&?����'^�*',+ úÐ'"%v-24�M� þºúG¡ q ~l9�&O�� 39*�������M�59<�?���?/0"L�4v/4�5$W�`�����I$M&O�7�����.�O�M�59�9�"%�-����24��$�"%�.�_9 ú���������� �-24$M�?�J�<��������9+s �{#' ���?/ � +s �{#'}� P �#~szpj ú þ ×2?9<"%�4v�$�&4":9}�.��$M�M"a�øú � /O/0"%�4v7�����W&4�J��9��J�?9<"%$�"%�s"%$<z�$���$M&4��+s �{#'��~?��9<�5/��5t%v-���M"L$M&4�]9,"%�����M�5�-9��59�$M&4�I��24�$M"L�.�59^~sz����4�-$M&4��� ù × ú

rH�0$�24"%$�"%�n�JtLz ÷��-/4/0"L�4v.�����W&4�J��9��J�?9<"%$�"%�s"%$<z�9<&4��24ta/N�J�O&?���?�K�!�?�J�����-�M���5�?��� ÷n�4�-$!/0��v��W�-/0�I"%$ ú]rÌ�l$M&4"a9�J�-9�� ÷}$�&4��"L�0���J��"%���7�?�J�����-�M���5�?��������$M&4�Ù�J���W&4�J��9��J��9�"%$�"%�n���5t%v-���M"L$M&4�]9�"a9`/02O��$M�­����2O�0������$M24�?�5$M�"%�s$M���W���K$M"%�-�`~?�J$< *�J�J�.$�&4�I/0"a9�;7�.�s/0�Jt�zk9�4�������J$y�i&4"L�4v|��tLv�����"%$�&4��9}�5�?/.$M&4��9��?�5��"¢uC�b~?�J&��_�s"%�-�#����$�&4�ñ õ��8mCU ò�ZWZ� *���M;st%�Ð��/íú {}&4�p/s������24tL$./s":9�;��.�s/s�Jt!�K���0u?v-24�M�_9`$M&4�Ù9��Jv-�.�J�s$M�5/ì�J���W&4��$����O�M�����J$y�i&/4�5$W���_��$M���`���5��/�&4"L$W9���9� }��t%t3��9��M�_��/��.":9�9��59 ú�{}&4� ñ õ��8mCU òMZWZI *����;0tL�n��/�������9�":9<$W9����|9<�J�?�5�W��$��9��_wx24���0$�":��t)9�$M���5���]98���3���5��/p�M�5wn24�59<$W9I����/� #�M"L$M���M�_wx24�_9�$W9����M�5�-/0"%�4v($M&4�724�?�K���.�4���59M9<�5/Nu?tL�7���?/ #�M"L$M"L�4v!$M&O�3�����.�O�M�59�9��5/!u?t%��� ú^{}&4�# #��"%$��#�M�5wn24�59<$W9�s�J�K24��"%��~424�y9�$y9)$��M"Lv�v����M�5/�~sz��5�N�5s�+\/4�5�J�.���$M&���$3�e���M"%�s/s":�J�5t%t%z�«?2?9<&4�593/0"%��$<z`~4tL�s�i;O9,���M�-��$M&O�&O�n9�$�/0"a9�;.~4tL�s�i;l�J�-�i&4�7��9��J�|9��_��$M"L���(FºúGFºúÝù5�ôú

�����?9<":/0����$M&O��9�"L$M2?�5$M"%�-�� #&4�J��$�&4�./s":9�;�":9|9��J���0"a��"%�Ov���~424�y9�$����3 #��"%$��`���5wx2O�59�$y9�����/����M�5�-/�M�_wx24�_9�$*�����M"%�n�_9, #&4�Ð9��I/4�5$W��"a9}���-�.�4t%��$M�JtLz��K���s$W��"L�4�5/`"L�.�����5��/l9��Jv-�.�J�s$^����$�&4�!���O�Y~?�n�5�W/(�J���W&4� ú�*���W&4�J��9����?9�"L$M"%�n�*�5t%v��-�M"L$M&4��9Rv�"L�n�}"L�.�.�5/0"a��$��^�4�M"L����"%$<zI$M�!$�&4�#�M�5�-/��M�5wn24�59<$ ÷-���?/��Y #"L$M&�$�&4�#/0�K����24tL$�4�������J$W�W&4"L�4v����-�0u?v-24�W�5$M"%�-���#$�&4�|/0":9<;."%�4"L$M"a��$M�_9}�79��J�J;l$M�7�4�M������$W�W&���/4/s"%$M"L���?�5t�/4��$y�`"%�s$M��$�&4�I�M�5�-/9���v��.�J�s$ úª¥}24$���9�9<�n���l��9^$M&4�*�M�5�-/����5wn24�59�$�":9�9M��$�":9Hu?�5/���M�-�®$�&4�}�-�4�Y~?�Ð���W/l�J���W&4� ÷�$�&4�#&4�Ð9�$M��~?�-9��5/9M�W&4�5/s24t%�J��"L�.�.��/0":�5$M�JtLz!":9�9�24�59�$M&4���4�J�s$}�?�J�?/0"L�4v� #��"%$��!�M�5wn24�59<$ ú�{}&4":9��4�M�J���.�4$W9�$M&4�!�O�M�����J$y�i&O"%�4v���K$M"%�s"%$<z|{ �e���M&?�5�?9.~e�K�����M�p$�&4��/0"a9�; �-��$M2���$M�-���J�n�J�����5���W&4�59�$M&O�p$W����v��J$(��zst%"L�?/0�J�7�K���s$W��"L�4"%�Ov$M&O��/4��$y��~4t%�s�W;O9$M�p�O�M�����J$y�i& ú � �­��/4/0"L$M"L���?�5t#9����J;����J$M2O�M�?9I$M&4��/s":9�;ì���K$M2?�5$M����$��p$M&4�]��z0tL"%�?/s�J����-�0$y��"%�O"%�4vp$�&4�(��24�M���J�s$�9�$��M�5�5� ���� #�M"%$����M�5wn24�59<$W9 ú�� "L$M&4�-24$7�J�-�i&4���H9<�J�?9�"L$M"L�0"L$�z ÷�$�&4�(9M�W&4�5/02Ot%�J� }�-24t:/.u?�4"a9�&�$�&4�I #�M"L$M��~O24�W9<$8~?�����-�M��9<�J�M�s":�K"%�4v|$M&4�|�M�5�-/N�M�_wx24�_9�$ ú#+n"L�?���I�.�n9<$#�M�5�-/N���5wx2O�59�$y9����-�ñ õ��8mCU ò�ZWZ!�5�M�.$�"%�.���YtL"%�7"�$��5/í÷?$M&4"a9�/0�n�_9�4�-$��4�5�K�59M9����M"Lt%zptL�J�4v�$�&4�J��$M&4�l���O�4t%"a�J��$�"%�����M2O��$M"L�.���Y"¢�$M&O� #��"%$��~O24�W9<$3�����.�Ot%�J$��59^~e�K�����M�|$M&4�I$�"%�.�3t%"L�."%$K�ôú

rY�}$�&4�7/0"a9�;��l�s/0�Jt��4�M������$W�W&4�59#���4tLz������M�_��/��."a9M9��_9��" ú � úÝ÷?�4��$I������2Ot%t^���5��/�&4"L$W9W�ô÷R$M&4�7�����W&4�J�9����?9�"L$M"%�n�l9M�W&4�5/s24t%"L�4vp�5t%v��-�M"L$M&4��9I�4�M�5�s":/0�]9�24�?�J��"%���7�?�J�����-�M���5�?��� ÷���9��.�_��9�2O�M�5/�~sz�~e�-$M&��.�5����M�_9��?���?9<��$�"%�.�59*���?/(���4�Ot%":����$M"L���(�M24��$M"L�.�59 ú}�b�)��tLtR$M&4�!��24tLt%��;0�O�� #tL�5/0v-���K���0u?v-24�W�5$M"L���?9 ÷�+s }�*{#' #"%$�&����5��/��."a9M9}�4�������J$y�i&4"L�4v�&?�-9�$�&4��tL�5 }�59<$8��24��$�"%�.�7�H�5t%$�&4��24v-&p"%$3":9!9<$M"Lt%t�9�tL"%v-&0$�t%z.&4"Lv�&4���8$�&?���$M&���$3���*���H��I�����ôú

Page 87: Aggressive Centralized and Distributed Scheduling ofDisk Requests

üJ�

} } FCFS~ ~ C-LOOK (LBN)� � SPTF� � SPCTF� � ASPTF(6)� � ASPCTF(6)

|�1.0 |�

2.0 |�4.0 |�

8.0 |�0

|�100

|�200

|�300

|�400

|�500

Number of Users

Mea

n Re

spon

se T

ime (

ms)

��

� ��

� ��

� ��

� ��

� ��

�������������! "��#%$���&(') *��&(+-,%�.&(�0/21435�

� � FCFS� � C-LOOK (LBN)� � SPTF� � SPCTF� � ASPTF(6)� � ASPCTF(6)

|;1.0< |;

2.0< |;4.0< |;

8.0<|=0

|=500

|=1000|=1500

|=2000

|=2500

|=3000

|=3500

Number of Users

Mea

n Ta

sk C

ompl

etio

n Ti

me (

ms)

��

��

��

��

��

��

��

��

��

��

��

��

�DCE���������!/F�G&(H!I2,%35+�J4�K'(14,%�L/�1M3N�

� � FCFS� � C-LOOK (LBN)� � SPTF� � SPCTF� � ASPTF(6)� � ASPCTF(6)

|�1.0 |�

2.0 |�4.0 |�

8.0 |�0

|�100

|�200

|�300

|�400

|�500

Number of Users

Mea

n N

on-C

ompu

te T

ime (

ms)

��

��

��

��

��

 

  

 

��YZ�*�!���[�!\],%��^(I2,%35+�$�'_�`/21435�

ãåäÛæ?> çéè êUì%@¢¡Üð8ACú-B4UDc òKB0�*'�2Ot%t%���!�4�5 #t%�5/sv�� � tLv��-�M"%$�&4�° �J�����-�M���5�?���

Page 88: Aggressive Centralized and Distributed Scheduling ofDisk Requests

üéþ

FCFS C-LOOKe SPTF£ ASPTF(6)¤ SPCTF¥ ASPCTF(6)¥Scheduling Algorithmh

0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

i

�H�x�kj��5�5���#�59<�e�-�?9��\{}"%�.�

FCFS C-LOOKe SPTF£ ASPTF(6)¤ SPCTF¥ ASPCTF(6)¥Scheduling Algorithmh

0

50

100

150

200

Appl

icat

ion

Run

Tim

e (s

ec)

l

��~�� � �4�Ot%":����$M"L�����#24�({}"%�l�

ãåä½æe> çéè êUìL@b¦ÜðËñ õ��8mCUôòMZWZK�^'424tLt%���!�4�5 #t%�5/0v-� � tLv�����"%$�&4�� ��J�����-�M���5�?���

Page 89: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ü P

í è-§R> è0ð¢�éä�õ³Û}ín�éçéèsõ4ù ¨ � �éä�ù äd©nõ-�éä�ô?ð2ª'"%v-24�M�_9 þ ú �njJÖ þ ú �n¡�9<&4�5 �$�&4���K¬��_��$W9#����$�&4��9<�5wn24�J�s$M":�5t�9�$��M�5�5� �-�4$M"L�."%¤_��$M"L���?9^�����I9��i&O�5/024tL"%�4v

ACú-BxX|û òKBºú}+n�5wn24�J�s$M"a��t?9<$M���5�����-�4$M"L�."%¤5�5$M"L���?9����-���M�5�-/`�M�5wn24�59<$W9^&?�J�n�#t%"L$M$�t%�#���*�4���K¬��_��$^���l�.�5����M�_wx24�_9�$I�M�59<�?���?9<�`$�"%�.�59 ú7'��-�I$M&4� ù���2?9���� ÷^F5�Y2�9��J� ÷^����/�����2?9����� }�-�M;st%�Ð��/49 ÷^���-�?�J��$��J�?�5$M"%�-���5��9��J�wn24�J�s$M":�5tn #�M"L$M�}���5wn24�59�$y9�"L�.�4�����n�_9e�.�5�5�I�M�59<�e�-�?9��#$�"%�.�_9�~0z ù × �-�^t%�59�9 ú�'4���^$�&4� f �Y2�9��J�^ *����;0tL�n��/U÷$M&O���.�5���p���59��?�-�?9��7$M"L�.�593/0�5�����5��9<��~0zÙ¡_Ö þ × ÷� #"L$M&����H��I����/0�����4�4"L�4v þºú ù × �Y$�&4��t:�5�Mv-�59�$|/0�J������5��9<�!�5�.���4vI$�&4�8��"%v�&s$*��tLv�����"%$�&4��9i� ú,������I�!�Ø�5t% #�JzO9�9M�W&4�5/024tL�59^9<�5wx2O�J�0$�":�5t4 #�M"L$M�59^"%�7t%�-v�"a�J��tLt%z��9����J�?/s"%�4v����y/0�J� ÷R�.~e��&?�J�0"L���I$M&?�5$|�J����/0��v��W�-/0�7�e�������������������� #&4����9<�J�M�s":��"L�4vl9��5wn24�J�s$M"a��t^ #��"%$M�9�$��M�5�5��9, #"L$M&(/0"a9�;O9}t:���W;s"%�4v| #�M"%$��!�4���J~420¬C�J��"%�4v���9��J�|9��_��$M"L��� þ úÝùøúGFº÷4�?�5v�� þºù�� ú�¥}z����-�?�J��$��J�?�5$M"%�Ov9�$��M�5�5��9#���*9<�5wx2O�J�0$�":�5tR #�M"%$��593��$!$�&4��&4�Ð9�$ ÷�$M&4���s24�7~?�J�}�5�#9<�5wn24�J�s$M":�5tR #�M"L$M�59#":9�9�24�5/�$M�.$�&4��/s":9�;"%��tL��v�"a�J��tLt%zl��9����J�?/0"L�4v����y/0�J��/0�5�����5��9<�59 ú

{}&4�!�.�_�����4�-�4�H�K���.�42O$M�#$M"L�.�59����«?�5�K$^$M&4�3"%�l�4�M�5�n�J�7�J�s$R"%�7�.�5�������59��?�-�?9��I$M"L�.�59��J��2�9��5/`~sz���-�?�J��$��J�?�5$M"%�-���5�*9��5wn24�J�s$M"a��tC #�M"%$��59 ú*'"Lv�24��� þ ú �С�~�9�&O�� 39#$M&O��l�5�����4�-�4�H�K���.�42O$M�I$M"L�.�59)���-�!�5�f ��2?9<�J�,Aeú�BxX|û òKB8 *���M;st%�Ð��/|/0�5�����5��9<"%�4v#~sz|jºú �5ÖsF úk¡ × �-9^�b���59�2Ot%$ ú^+s �{#'(���?/`+s }�*{#'�"%�.�4���5�n�$�&4��.�Ð9�$#��Fºúk¡ × � ÷�����t%tL�5 }�5/�~sz�$�&4�!�5v��J��9����?9�"L$M"%�n�3+s �{#'��~?��9<�5/.��tLv��-�M"%$�&4��9}� ùøú � × �ôú�{}&s2?9 ÷n$M&O�!+s �{#'�~?�-9��5/���tLv��-�M"%$�&4��9����K$M2?�5t%t%z��-24$M�?�J�<������� ���H��I���� #&O�J�.2?9<"%�4v7�|9�zO9�$M���.�YtL�J�n�JtC�Y" ú � ú ÷n���4�Ot%":����$M"L���4�9��?�5�K"�uC�����?�J�<�����M�]���?���3�.�J$��M"a�øúR{}&4"a9,"%��/0":�J�5$M�59^$�&?��$3���H��I����zk9,"L�.�4�����n���`�J�s$R"%�l�.�5�������59��?�-�?9��$M"L�.��"a9!�4�M�-~?��~4tLz�/s24�`$���~e��$M$M���&����?/0tL"%�4v(����$M&4�7~424�y9�$W9I���� #�M"%$��`���5wn24�59�$y9!":9M9<24�5/p~0zp$�&4���Ns-+�J�-�i&4��«?2?9<&./4�5�J�.�-�Üú � t%$�&4��24v-&`"L$"a9"%�l�e�-�M$y���s$^$M�I9<�J�M�s":�K�#9�2��i&�~?�-�i;sv�����24��/����5wx2O�59�$y9��Z«]��"L�J�0$�t%z ÷"%$3":93�.�����"L�.�?����$W���s$3$M��9<�J�M�s":���|����"%$�":�J�5tR�M�5wn24�59<$W9���� ú vÉúÝ÷4�M�_��/��M�_wx24�_9�$W9#�����! #&4"a�i&(�4�M�s�K�59M9<�59!�����~4tL�s�i;s"%�4vs�ôú�{}&?�5$,"a9 ÷�"L�.�4�����n�_/!9��J���0"a���^�����^~����W;0v-�M��2O�?/� #�M"L$M�}���5wn24�59�$y9���Ot%zI"%�.�O�M�5�n�59��5�4�4tL":�J�5$M"%�-��M2O��$M"L�.�59^"%��/0"%���5��$MtLz��Y"¢���5$!�5t%tY� ÷0 #&4���M�5�-9b"L�.�4�M�5�n�5/79����M�s":���8���-�#&4"%v-&��4��"%�-�M"%$<z7�M�5wn24�59<$W9}$<zs�4":�J�5t%tLz��tLt%�5 39#���4�M�s���_9M9#$M��u?�4"a9�&(�.�����Iwx2O":�W;0tLz ú

'"%v-24�M� þ ú �-�Nv-"%�n�593$M&4���.�_���p�M�_9��?���?9<�`$�"%�.�_98�5�?/��5�4�4tL":�J�5$M"%�-�p�M24��$M"L�.�59,���-�$�&4� ñ õ��8mCU ò�ZWZ }�-�M;st%�Ð��/íú����-�?�J�5$M�J�?�5$M"L�����5�?/�9��5wn24�J�s$M"a��t�9��i&4�_/024t%"L�4v������M�5�-/��M�_wx24�_9�$W9I/0�n�_9��4��$\�_¬C�5��$|$M&4�59<��?�J�����-�M���5�?���p�.��$M�M"a�J9 ú®���-�?�J�5$M�J�?�5$M"L�����5�79��_wx24���0$�":��t3 #�M"L$M�59."L�.�4�M�5�n�59��l�5�����M�59<�e�-�?9��ì$M"%�l�59~sz�¡ × �������5t%t4�5�R$�&4�#9��i&4�_/024t%"L�4vI�5t%v��-�M"L$M&4��9 ú�{}&4�}u?t%�3�K���.�4���59M9<"%�-�����-�.�4t%��$M�59Rj ú þ_Öxjºú fx× ����9<$M�J�)��9�8���59�24tL$ ú����H��I����~?�J�4��u�$W9$�&4�}�.�Ð9�$*�Hj ú fx× ���������®$�&4":9��?����$M":�K24t:�5��-�4$M"L�."%¤5�5$M"L���Üú�{}&4"a9"%�?/s":�J�5$M�59$M&O�8����������"a9��O��$^�-�4t%z|9����M�s":��"L�4v#$M&4�#~����W;0v-�M��2O�?/� #�M"L$M�59R�Z«]��"%�J�s$MtLz ÷�"L$"a9�5t:9<�!�4�M�5�s":/0"L�4v3~e��$M$M���9����M�s":���8���-�#$M&4�|����"%$�":�J�5t��M�_wx24�_9�$W9}"L��$M&4� ñ õ��8mCU ò�ZWZ�$M�W�-��� ú

íªî�ï è.u>�ÛÛä�ð æwv äx�5ïÚã­¬ ã8í®¬|ô?ù�ù�õ4ð¯u±°�>¿ès>¿è.u³² äDª�÷�ª'"%v-24�M�_9Õþºú � þJÖ þºú � f v�"L�n�!�?�J�����-�M���5�?����/4��$y������#&4�Ð9�$M��~?�-9��5/p���H��I���Ëú���� ú�+O+s��9��i&O�5/024tL"%�4v|���

ACú-BxX|û òKB`2?9�"L�4vl/0":9<;498 #"L$M&Ù')�*',+]�����l�����?/lwx24��24�J"%�Ov ú3{}&4��~?�5�Mv��y���4&�9�5t:9<��9�&4�5 Ø&4�Ð9�$M��~?�-9��5/+s �{#'Õú¢��� ú�+4+s���5�?/�+s }�*{#'Õú���� ú¢+4+s����tLv��-�M"%$�&4� �?�J�<�����������?�K���Y2?9<"%�4v��4�-�4�Hwn24�J2O�5/�/s":9�;O9i�#���-��M�K���J�M�J����� úµ´|'4���� ^�M�59<�J�J;I�5�?/�'424t%ts�K���.���5�?/!wn24�J24��"%�4v������su?v�24�y��$�"%����9 ÷n�!�K���.���5�?/!wn24�J24��tL�J�4v�$�&����$< }�.�4���5�0"a/0�598$�&4�`~?�59<$I�.�5���(�M�59<�?���?9<�`$�"%�.�59#�M��vn���y/0t%�_9M9!����$M&4���s24�7~e���8�5�#2?9<�J�W9 ú � t%tL�5 #"%�4v24�.$���$< }���K���.���5�?/49�wn24�J24�5/7��$#�_���W&�/0":9<;`tL�5 }�J�y9)�l�5���.���59��?�-�?9��I$M"L�.�59~sz7��Ö ù�j × ���-�3 ^�M�59<�J�J;���-�.������/�wn24�J24��"%�4v��5�?/ÖùK��ÖsF-j × �����l'�2Ot%t#�K���.���5�?/�wn24�J24��"%�4vÉú�{}&4��"%�.�4���5�n�J�`���0$!"L���.�5����M�_9��?���?9<��$�"%�.�3"%�?�K�M�5�-9��59} #"L$M&�$M&4�I�s24�7~e���,�5��2?9<�J�W9 ú¶M²�³0µ5¶K³Y·:¸:¹-´W³Yº�»�¼%·e¾�¿�À�´iÁkÂK¶KÃYÄk·�µ5Å8³5Ã�º<ÁkÒ^¶KÆ�ÇHÈ�Ã�Ã�º�Æ�·4ÉJÆ5¶WÊRÁkº�»JÂ�º4¶WË5¶KÆJ¸:¹�¶�´WÃH»^»5´W·H´RÇ<´KÇYµ5ºRÇH¶KÆJ·Yº<ÆJ·�³O´iÆ-»�´�ÇH·�È-´i·�¶�Ã

Í�¶K³�Äk·YÄG¶�Æ5³�ÎJ·Yµ5º<ÒI»J¶}Æ5¶K·R³HÇYµ5º�»JÈ5Ákº�ºÌÏк�ÇÌ·�ÄkÑKº<ÁkÒ8ËL¶�ê»JÄk³YÉ�³RÊRÄk·Yµ�Ç̶KÅ3Å!´WÆ-»}Ó�È5º<È5º�ÄGÆ�Â-Ô

Page 90: Aggressive Centralized and Distributed Scheduling ofDisk Requests

üøü

Scheduling Algorithm¸0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

�(¼x�kj¾½%¼%¿��)½59<�bÀÁ¿?9½\{­ÃÅÄƽ

Scheduling Algorithm¸0

50

100

150

200

250

Mea

n N

on-C

ompu

te T

ime

(ms)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

��~��Çj¾½%¼%¿�ë`À�¿EÈ_É]À�Ä.�O2EÊt½|{­ÃÅÄL½

Ë)ÌDÍ?>¯ÎGÏÑÐFÒÅÓ¢Ô�Õ8ACú-BxX|û0ÖKB-×�ØÙo!9½�Ú��,+�½_wx2E½Û¿-ÊÜÃx¼�t�+.ÝKÞE½5/024tßÃÅ¿4v � t%vÁÀ�ÚÜÃÅÊtÞàÄâá2½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½

Page 91: Aggressive Centralized and Distributed Scheduling ofDisk Requests

å f

Scheduling Algorithm¸0

20

40

60

80

100

120

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

�(¼x�kj¾½%¼%¿��)½%æ<�bÀÁ¿¢æ½\{­ÃÅÄƽ

Scheduling Algorithm¸0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

��~��Çj¾½%¼%¿�ë`À�¿EÈ_É]À�Ä.�àçEÊt½|{­ÃÅÄL½

Ë)ÌDÍ?>¯ÎGÏ|ÐFÒßÓRQbÕ#ACú-BxX|û0ÖKB-×?F!o0æ½�Úèæ��­é�½_wêçE½Û¿-ÊÜÃx¼�t¯é.ÝKÞE½%ë-ç4tßÃÅ¿4v � t%vÁÀ�ÚÜÃÅÊtÞàÄìá2½ÛÚÂãdÀ�ÚÜÄí¼G¿îÝZ½

Page 92: Aggressive Centralized and Distributed Scheduling ofDisk Requests

å q

Scheduling Algorithm¸0

50

100

150

200

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

�(¼x�kj¾½%¼%¿��)½%æ<�bÀÁ¿¢æ½\{­ÃÅÄƽ

Scheduling Algorithm¸0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

��~��Çj¾½%¼%¿�ë`À�¿EÈ_É]À�Ä.�àçEÊt½|{­ÃÅÄL½

Ë)ÌDÍ?>¯ÎGÏ|ÐFÒßÓnïnÕ#ACú-BxX|û0ÖKB-×4�Lo0æ½�Úèæ��­é�½_wêçE½Û¿-ÊÜÃx¼�t¯é.ÝKÞE½%ë-ç4tßÃÅ¿4v � t%vÁÀ�ÚÜÃÅÊtÞàÄìá2½ÛÚÂãdÀ�ÚÜÄí¼G¿îÝZ½

Page 93: Aggressive Centralized and Distributed Scheduling ofDisk Requests

f j

Scheduling Algorithm¸0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

�(¼x�kj¾½%¼%¿��)½%æ<�bÀÁ¿¢æ½\{­ÃÅÄƽ

Scheduling Algorithm¸0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

��~��Çj¾½%¼%¿�ë`À�¿EÈ_É]À�Ä.�àçEÊt½|{­ÃÅÄL½

Ë)ÌDÍ?>¯ÎGÏ|ÐFÒßÓ?@qÕ#ACú-BxX|û0ÖKB-× f o0æ½�Úèæ��­é�½_wêçE½Û¿-ÊÜÃx¼�t¯é.ÝKÞE½%ë-ç4tßÃÅ¿4v � t%vÁÀ�ÚÜÃÅÊtÞàÄìá2½ÛÚÂãdÀ�ÚÜÄí¼G¿îÝZ½

Page 94: Aggressive Centralized and Distributed Scheduling ofDisk Requests

f Ø

Scheduling Algorithm¸0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

�(¼x�kj¾½%¼%¿��)½%æ<�bÀÁ¿¢æ½\{­ÃÅÄƽ

Scheduling Algorithm¸0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

ðNo Opt.CW.CW.CR.CW.SSR

C-LOOK¹ LOOK¹ SSTFº VSCAN(0.2) SPTF ASPTF(6) SPCTF» ASPCTF(6)»

��~�� � �4�OtÅÃxÝÛ¼GÊtÃßÀ�¿��)çE¿({­ÃÅÄL½

Ë)ÌdÍ?>2Î%ÏwÐFÒßÓ¢ÓqÕòñ]ó��8mCUôÖMZWZK�]é�½5w�çE½�¿.ÊtÃx¼5t2é.ÝKÞE½%ë.ç4tÅÃß¿4v � tLv�ÀÁÚtÃÅÊÜÞEÄâá2½ÛÚÂãdÀ�ÚÜÄí¼G¿îÝZ½

Page 95: Aggressive Centralized and Distributed Scheduling ofDisk Requests

f F

Scheduling Algorithmõ0

20

40

60

80M

ean

Res

pons

e T

ime

(ms)

öCQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û ¼êükj¾½%¼%¿¾ý)½%æ_þbÀÁ¿¢æ½òÿ­ÃÅÄƽ

Scheduling Algorithmõ0

50

100

150

200

250

300

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û�� üÇj¾½%¼%¿��`À�¿EÈ_É]À�ÄÆþàçEÊt½Ùÿ­ÃÅÄL½

Ë)ÌDÍ��¯Î%ÏwÐFÒÅÓnÐFÕ��eú��|û0Ö��-×¢Ø)o æ½�Ú�� é.ÝKÞE½%ë-ç� ÅÃÅ¿����� ���ÀÁÚtÃÅÊÜÞEÄ á2½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½]ãdÀ�Ú��`Ã��F½�Út½Û¿-Ê]É]À�ÄÆÈÄä¼G¿¢ë��`çE½�çE½��n½�¿���ÊÜÞ¢æ

Page 96: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��

Scheduling Algorithmõ0

20

40

60

80

100M

ean

Res

pons

e T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û ¼êükj¾½%¼%¿¾ý)½%æ_þbÀÁ¿¢æ½òÿ­ÃÅÄƽ

Scheduling Algorithmõ0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û�� üÇj¾½%¼%¿��`À�¿EÈ_É]À�ÄÆþàçEÊt½Ùÿ­ÃÅÄL½

Ë)ÌDÍ��¯Î%ÏwÐFÒÅÓ¢a�Õ��eú��|û0Ö��-×�� o0æ_½�ÚKæK� é.ÝKÞE½%ë-ç� ßÃÅ¿�� �! "��ÀÁÚtÃßÊtÞEÄ á2½�Ú_ãdÀ�ÚÜÄí¼G¿¢Ý�½|ãdÀ�Ú#�`Ã��F½�Út½Û¿-ÊÉ]ÀÁÄÆÄí¼%¿¢ë$�`çE½�çE½%�n½�¿���ÊtÞîæ

Page 97: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�'&

Scheduling Algorithmõ0

50

100

150

200M

ean

Res

pons

e T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û ¼êükj¾½%¼%¿¾ý)½%æ_þbÀÁ¿¢æ½òÿ­ÃÅÄƽ

Scheduling Algorithmõ0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û�� üÇj¾½%¼%¿��`À�¿EÈ_É]À�ÄÆþàçEÊt½Ùÿ­ÃÅÄL½

Ë)ÌDÍ��¯Î%ÏwÐFÒÅÓnmFÕ��eú��|û0Ö��-× & o0æ_½�ÚKæK� é.ÝKÞE½%ë-ç� ßÃÅ¿�� �! "��ÀÁÚtÃßÊtÞEÄ á2½�Ú_ãdÀ�ÚÜÄí¼G¿¢Ý�½|ãdÀ�Ú#�`Ã��F½�Út½Û¿-ÊÉ]ÀÁÄÆÄí¼%¿¢ë$�`çE½�çE½%�n½�¿���ÊtÞîæ

Page 98: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�(

Scheduling Algorithmõ0

100

200

300

400M

ean

Res

pons

e T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û ¼êükj¾½%¼%¿¾ý)½%æ_þbÀÁ¿¢æ½òÿ­ÃÅÄƽ

Scheduling Algorithmõ0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û�� üÇj¾½%¼%¿��`À�¿EÈ_É]À�ÄÆþàçEÊt½Ùÿ­ÃÅÄL½

Ë)ÌDÍ��¯Î%ÏwÐFÒÅÓ¢¡�Õ��eú��|û0Ö��-× � o0æ_½�ÚKæK� é.ÝKÞE½%ë-ç� ßÃÅ¿�� �! "��ÀÁÚtÃßÊtÞEÄ á2½�Ú_ãdÀ�ÚÜÄí¼G¿¢Ý�½|ãdÀ�Ú#�`Ã��F½�Út½Û¿-ÊÉ]ÀÁÄÆÄí¼%¿¢ë$�`çE½�çE½%�n½�¿���ÊtÞîæ

Page 99: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�)

*EÀ�Ú!ÊtÞE½ ØZÈdç¢æ_½�Ú�×+�GÈdç¢æ½ÛÚ�×)¼%¿¢ë & ÈDç¢æ_½�Ú-,­À�Ú/.0 ßÀ�¼ÁëEæZ×­ÊÜÞE½íÄƽ%¼%¿ ¿EÀ�¿àÈ(ÝZÀÁÄÆþEçEÊܽíÊtÃÅÄL½21Á¼GÚÜÃŽ%æ ÀÁ¿� "3æ4 ßÃ"�ÁÞ-Ê/ "3 û çEþ ÊtÀ5�06 ��7 ü ãdÀÁÚ5Äí¼'8.ÃÅÄ�çEÄ ÝZÀ�ÄÆÄä¼G¿¢ë59êçE½ÛçE½: Ž�¿���ÊtÞîæ À%ã5ØÁ×;�.× & ×2¼%¿¢ë Ø ) 6!ÿ­ÞE½!Äƽ%¼G¿Út½[æÂþ¢À�¿¢æ_½�ÊtÃßÄƽ5ë-Ã<�n½ÛÚt½�¿¢Ý�½ � ½�Ê=,ǽ�½�¿¾Ää¼'8.ÃÅÄ�çEÄ>9�çE½�çE½% Ž�¿���ÊtÞîæ À%ã0ØÙ¼G¿îë?��Ãxæ)À�¿� �35@06A�CB¢ØD6ÅØ 7 6�*EÀÁÚÊtÞའ� ÈDçîæ½�Ú:,ÇÀ�ÚE.F ÅÀ ¼�ën×]ÞEÀG,­½H1�½�Ú�ׯÊtÞE½ÆÄä¼'8.ÃÅÄ!çEÄ ÝZÀÁÄÆÄí¼%¿¢ë?9êçà½�çE½I ß½�¿���ÊÜÞ � ½H��ÃÅ¿îæ ÊtÀ?1.ÃxæÂà � "3 ¼�ãdÈãd½%ÝZÊ!ÊtÞཾÄƽ%¼%¿ ¿EÀ�¿EÈ�ÝZÀÁÄÆþEçEÊܽ¾ÊtÃßÄƽ û�� 3 çEþ³ÊÜÀ & 6 ��7 üJ6K�� " ßÀG,)ÃÅ¿��ÑÊ=,­À ÝZÀ�ÄÆÄä¼G¿¢ëEæ%9êçà½�çE½%ë þb½ÛÚë-à æ4.¾ÃßÄÆþEÚÜÀ'1�½[æ­Äƽ%¼G¿ ¿EÀ�¿àÈ(ÝZÀÁÄÆþEçEÊܽ�ÊtÃßÄƽ%æ � 3?� 7 ãdÀ�ÚÙá*Út½%æ_½�½C. ÝZÀ�ÄÆÄä¼G¿¢ëL9�çE½�çE½�Ãß¿��L¼G¿¢ë ��7 ãdÀÁÚ*Eç� " ÇÝZÀÁÄÆÄí¼%¿¢ëM9�çE½�çà½�ÃÅ¿���6?�� � ÅÀG,)ÃÅ¿��íãdÀ�çEÚòÝZÀ�ÄLÄí¼G¿¢ëàæ ÃßÄÆþEÚÜÀ'1�½[æ þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½ � 3 ¼G¿EÀÁÊtÞE½ÛÚ-� 7 6r(¿¢ÝZÚܽ%¼�æ_ÃÅ¿��íÊtÞà½íÝZÀ�ÄLÄí¼G¿¢ë59êçà½�çE½- Ž�¿��ÁÊtÞ � ½C3�À�¿¢ëÑãdÀ�çEÚ � ½H��ÃÅ¿îæNÊtÀ ë-½C�ÁÚK¼�ë.½�þ¢½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½ ×2¼ÁæNÊÜÞE½ÞEÀ æÂÊtÈ � ¼Áæ½%ë ætÝKÞE½%ë-ç� Ž�ÚN ßÀ�æ½[æ ÄÆÀÁÚt½Ù¼G¿îë¾ÄÆÀ�Úܽ0ÀGãÇÃÅÊèæ ¼ � Ã" ßÃÅÊ=3ÆÊÜÀÆë03.¿¢¼%ÄÆÃxÝ�¼G " �3�Úܽ�À�Úèë-½�Ú`ÊtÞE½Ùþb½Û¿¢ë-ÃÅ¿��Út½O9êçE½[æÂÊKæ�6*2Ã"�ÁçEÚt½ ( 6 &QP �ÁÃ"1�½%æ`ÊtÞE½�Äƽ[¼G¿ÑÚt½[æÂþ¢À�¿¢æ_½�ÊÜÃÅÄƽ[æ ¼%¿¢ë|¼%þEþ� ßÃxÝ�¼%ÊtÃÅÀÁ¿ÑÚtçE¿ ÊtÃßÄƽ%æ ãdÀÁÚNÊÜÞE½ ñ]ó���RTSôÖ/UJU

,­ÀÁÚE.F ÅÀ ¼�ë�ç¢æÂÃß¿�� ÊÜÞE½`æt¼%Äƽ)ÚK¼%¿���½0À%ã�Äí¼G8-ÃßÄ�çàÄ ÝZÀ�ÄLÄí¼G¿¢ëV9�çE½�çE½! Žۿ���ÊÜÞ¢æW6X�Y9�çE½�çE½N ß½�¿��ÁÊtÞ!ÀGã�Ê=,ÇÀþEÚÜÀ'1.Ãxë.½%æ­ÊtÞE½ � ½%æ_Ê þ¢½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½ ×-ÃÅÄLþEÚtÀG1.ÃÅ¿��5Äƽ%¼%¿ÆÚt½[æÂþ¢À�¿¢æ_½ ÊÜÃÅÄƽ%æ � 3 (�7 ¼%¿¢ë|ØH@ 7 ãdÀ�Ú á*Út½%æ_½�½C.¼G¿îëZ*îç� " `ÝZÀÁÄÆÄí¼G¿îë[9�çE½�çà½�ÃÅ¿��à× Úܽ%æÂþ¢½%Ý�ÊtÃ"1�½H "3\6Z*EÀÁÚ � À�ÊÜÞ ÝZÀ�¿F]���çEÚè¼GÊÜÃÅÀ�¿îæZ× ÊÜÞE½Ñ¼%þEþ� ßÃxÝ�¼%ÊtÃÅÀÁ¿³ÚtçE¿îæØ6^� 7 ÄLÀ�Út½�9êçEà Ý_.F "3:,)ÃßÊtÞ ¼!ÝZÀ�ÄÆÄä¼G¿¢ë-9êçà½�çE½V Ž�¿���ÊtÞíÀ%ã*Ê=,­À�6

`!a/bca�d e�f�g>gihkjFlnmco?pqmsr!tvuEf!w�x=mNr!w�0æ)æ½[ÝZÊtÃßÀ�¿ ( 6ÅØ0þEÚܽ%æ½�¿.ÊKæ)¼y ¼GÚ/��½5¿-çàÄ � ½�Ú]ÀGã�½C8.þ¢½�ÚtÃßÄƽ�¿.ÊKæZ×%ÃÅÊ)à æ ç¢æ_½Zãdç� �ÊÜÀ�Út½%æ_ÊK¼GÊܽ5æÂÀÁÄƽ0À%ã*ÊÜÞE½

Äí¼'z_ÀÁÚ)ÝZÀÁ¿¢ÝW ßç¢æÂÃßÀ�¿¢æK�é�½�½C..ÈdÚt½%ë-çîÝZÃÅ¿��L¼' ���ÀÁÚtÃÅÊÜÞEÄíæ`ë-ÀÆ¿EÀÁÊ0Út½O9êçEÃßÚt½òë-½�ÊK¼%Ã" ß½%ë Äí¼%þEþEÃß¿���æ)ÀGã+ ÅÀD��à Ý�¼' � ÅÀ.ÝJ.àæ ÊtÀÆþàÞ03àæÂà Ý�¼'

Äƽ%ë.Ãx¼� ßÀ.Ý�¼GÊÜÃÅÀ�¿îæZ×¢æÂÃß¿¢ÝZ½! ÅÀD��ÃxÝÛ¼' �¼Áë'zܼ�Ý�½�¿¢ÝW3:�Á½�¿E½�Úè¼' " �3�ÃÅÄÆþ� ÅÃŽ[æ2þEÞF3Eæ_ÃxÝ�¼G n¼Áë'zܼ�Ý�½�¿¢ÝW3�Ãß¿ÆÄÆÀ.ë-½�ÚÜ¿Æë.Ãxæ4.ë-ÚÜÃ"1�½%æ�6ÿ ¼O1.ÃÅ¿��5¼�Ý�Ý�½%ætæ2ÊÜÀÙ¼�Ý�ÝZçàÚK¼GÊܽ`ëE¼GÊè¼� x¼C3�À�çEÊ�Äí¼GþEþàÃÅ¿�� æ2À�¿� �3 Äí¼%ÚE�ÁÃÅ¿¢¼G " "35ÃßÄÆþEÚtÀG1�½%æ�æÜÝôÞà½%ë-ç� ßÃÅ¿��þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½5ãdÀ�Ú5æ_ç¢ÝôÞ ¼G "�ÁÀ�ÚtÃßÊtÞEÄäæW6V� ÄÆÀÁ¿��!ÊtÞE½!æ_½�½C..ÈDÚܽ%ë-ç¢ÝZÃß¿��L¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæZ×�É]È{�;|V|~} Ãß¿-Êܽ�ÚK¼ÁÝZÊKæ� ½%æÂÊ~,)ÃÅÊtÞ À�¿EÈ � À�¼%ÚKë|þEÚܽZãd½�ÊèÝôÞEÃß¿��!Ý�¼ÁÝôÞE½[æW60ÿ­ÞàÃxæ)Út½%æ_ç� ÅÊèæ ÃÅ¿5 ÅÀG,­½�Ú`Äƽ%¼%¿íÚt½%æ_þbÀÁ¿¢æ½�ÊÜÃÅÄƽ[æ ãdÀ�Ú0ÄÆÀ æÂÊÀGã"ÊtÞE½V,­ÀÁÚE.F ÅÀ ¼�ëEæ)æ_Êtç¢ë-Ãß½%ëí¼G¿¢ëíÃÅ¿¢Ý�Út½%¼Áæ½%ëíæ43àæÂÊܽ�ÄÆÈ� ŽC1�½H Eþ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½ ãdÀÁÚ)ÊtÞE½0ãdç� � ¯æ43àæÂÊt½ÛÄìÊtÚè¼�ÝZ½%æ�6�� "�ÁÀ�ÚÜÃÅÊtÞàÄíæ*ë-½%æ_Ã"�Á¿E½%ë�ÊtÀ5Út½%ë.ç¢ÝZ½ ÝZÀ�Ä � ÃÅ¿à½%ë æ_½�½C.�¼%¿¢ë�ÚÜÀ�ÊK¼%ÊtÃßÀ�¿¢¼G � x¼%Êt½�¿îÝW3�ë-½H x¼C3Eæ*ÚܽG9êçàÃÅÚt½`¼ÁÝ�ÝZçEÈ

ÚK¼%Êt½� ßÀ�ÁÃxÝ�¼G ÅÈdÊtÀ�ÈdþEÞF3Eæ_ÃxÝ�¼G nÄí¼%þEþEÃß¿���æ�×-æ_½�½C.!ÝZçàÚE1�½%æ�×êÞà½%¼�ëíæ4,)ÃßÊKÝKÞ�ÊÜÃÅÄƽ[æZ×�ÝZÀÁÄÆÄí¼%¿¢ë�¼G¿¢ëíÝZÀÁÄÆþ� ß½�ÊtÃßÀ�¿ÀG1�½�ÚtÞà½%¼�ëEæ�×GÚÜÀ�Êè¼GÊtÃßÀ�¿òæÂþ¢½�½%ëEæ�×�¼%¿¢ëy..¿EÀG,N Ž%ë0�Á½]ÀGãFÝZçàÚtÚt½Û¿-Ê ¼�ÝZÊÜ碼GÊÜÀ�Ú*þ¢À�æ_ÃÅÊÜÃÅÀ�¿îæW6*ÿ­ÞàÃxæ�ÃÅ¿-ãdÀÁÚtÄí¼%ÊtÃÅÀÁ¿Ù¼' ÅÈ ÅÀG,`æ�¼`ætÝKÞE½%ë-ç� Ž�ÚFÊtÀ ¼�Ý�ÝZçàÚK¼GÊܽC "3`þEÚܽ%ë-ÃxÝ�ÊnÃÅ¿àÃÅÊtà ¼GÊÜÃÅÀ�¿Ùë-½H x¼C3EæEãdÀ�Ú¯þ¢½�¿¢ë-Ãß¿��)Út½G9�çE½%æ_ÊKæ�¼%¿¢ëNÊÜÞE½�Út½ � 3 æ½C ß½%ÝZÊ� ½�ÊtÊܽ�Ú0ÚܽG9êçà½%æÂÊ5æÜÝôÞà½%ë-ç� ß½%æW6�é�ç � æ=3Eæ_Êt½�Ä ¼%¿¢ë æ43àæÂÊt½ÛÄ Äƽ�ÊÜÚtà Ý�æ­ÃÅ¿¢ë.ÃxÝ�¼%Êt½�ÊtÞî¼GÊÙæÂç¢ÝKÞ¾ãdç� � ÅÈ�.-¿EÀG,N ß½%ë0��½¼' ���ÀÁÚtÃÅÊÜÞEÄíæ)ÀGãdÊܽ�¿¾þEÚÜÀG1-à ë-½ ÊÜÞE½ ÞEÃ���ÞE½[æÂÊ� ß½C1�½C xæ­À%ãÇþb½ÛÚÂãdÀ�ÚÜÄí¼G¿îÝZ½\6!*EÀ�Ú`½C8-þ¢½�ÚÜÃÅÄƽۿ-Êèæ ç¢æ_ÃÅ¿��ÆÊÜÞE½�ë.Ãxæ4.Út½O9êçE½[æÂÊ)ÊtÚè¼�ÝZ½[æZ×�é.á]ÿN*2È � ¼�æ½[ëѼ' "�ÁÀ�ÚÜÃÅÊtÞàÄíæ­ÊtÞ¢¼%Ê Ãß¿¢ÝZÀÁÚtþ¢À�Úè¼GÊt½:..¿EÀG,N Ž[ë0��½5ÀGãÇÀÁ¿EÈ � À ¼GÚKë Ý�¼ÁÝôÞE½Ùæ_ÊK¼GÊܽ¼�ÝKÞEÃß½C1�½)ÊtÞE½! ÅÀG,ǽ%æÂÊÇÄƽ%¼G¿�Úܽ%æÂþ¢ÀÁ¿¢æ½5ÊtÃßÄƽ%æqãdÀÁÚ­ÄÆÀ æÂÊÇæÂç � È(æܼGÊÜçEÚK¼%ÊtÃÅÀÁ¿L,­À�Ú/.0 ßÀ�¼ÁëEæW6+*EÀ�Ú­½H8-þ¢½�ÚÜÃÅÄƽ�¿.ÊKæç¢æ_ÃÅ¿�� ÊtÞE½�ãdç� " Çæ=3Eæ_Êt½�Ä ÊÜÚK¼�Ý�½%æZ×]é.á]ÿN*2È � ¼�æ½[ë ¼G "�ÁÀ�ÚtÃßÊtÞEÄäæ�,)ÃßÊtÞ Ý�¼�ÝKÞE½�È�æ½ۿ¢æÂÃßÊtÃ"1.ÃÅÊ=3íþEÚÜÀ'1.Ãxë.½�ÞEÃ���ÞE½ÛÚþ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½`à ã¯ÊÜÞE½5ë-à æ4.!ÄÆÀ.ë-½C ¢À�¿� "3!þEÚt½Zãd½ÛÊKÝKÞE½%æ*À�¿íÚt½[¼�ë�ÄÆà ætæ_½%æ û Ã{6 ½\6Å×Á¿EÀ�Ê)ÀÁ¿ Úܽ%¼�ë!ÞEÃÅÊèæôüJ6c|`ÊÜÞE½�ÚtÈ,)Ãxæ_½�×�¼%¿�çE¿.ãdÀ�ÚtÊÜçE¿¢¼%Êt½`ÃÅ¿.Êt½�Úè¼�ÝZÊÜÃÅÀ�¿ÙÀ.Ý�ÝZçEÚèæ � ½ÛÊ4,ǽ�½�¿�ÊÜÞE½N,­ÀÁÚE.F ÅÀ�¼Áë�¼G¿¢ë�ÊtÞà½)þEÚt½Zãd½ÛÊKÝKÞEÃÅ¿�� ¼' "�ÁÀ�ÚÜÃÅÊtÞàÄÑ×Äí¼G.-Ãß¿���Ý�¼ÁÝôÞà½�È(æ_½�¿¢æ_ÃÅÊtÃ�1-ÃßÊ=3�ÃÅ¿¢¼Áë01-à æt¼ � Ž\6

rDã�¼�,ÇÀ�ÚE.F ÅÀ ¼�ëÆÝ�À�¿.ÊK¼GÃß¿¢æ*¼5æÂÃ���¿EÃ<]FÝ�¼%¿-Ê*ãdÚK¼ÁÝZÊtÃßÀ�¿�À%ã¯æ½O9êçE½Û¿-ÊÜÃx¼' àÚt½G9�çE½%æ_ÊKæZ× ¼ ÞàÀ�æÂÊÜÈ � ¼�æ½[ëÆætÝKÞE½%ë-ç� Ž�ÚÝ�¼%¿ ÃÅÄÆþàÚtÀG1�½ þ¢½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½ � 3 ÝZÀ�¿¢ÝÛ¼GÊt½Û¿¢¼GÊÜÃÅ¿�� æ½G9�çE½�¿.Êtà ¼' *ÚܽG9êçà½%æÂÊèæNÃÅ¿.ÊtÀÆãd½C,ǽ�Ú�×v ¼GÚE�Á½�Ú ÚܽG9�çE½%æÂÊèæW6ÿ­ÞEà æ Êܽ%ÝKÞE¿EÃ�9�çE½ÙÚt½%ë-çîÝZ½%æ0ÊtÞE½!ÊtÀÁÊK¼G ­Ý�À�ÄÆÄí¼%¿¢ë¾¼%¿¢ë ÝZÀ�ÄÆþ� Ž�ÊÜÃÅÀ�¿ ÀG1�½�ÚtÞE½[¼�ëEæ0ÃÅ¿îÝZçEÚtÚܽ%ëѼGÊÙÊtÞE½!ë.Ãxæ4.¼G¿îë � ½�ÊtÊܽ�Ú]çEÊtÃ� ÅÃ"�Û½%æqÊÜÞE½`À�¿EÈ � À�¼GÚèëíëE¼GÊè¼ Ý�¼ÁÝôÞE½Q6��� ßÊt½�ÚÜ¿¢¼GÊܽC "3�×Á¼5ætÝKÞE½%ë-ç� Ž�Ú]ÝÛ¼G¿LæÂÀ�ÄL½�ÊtÃßÄƽ%æ�ÃÅÄÆþEÚÜÀG1�½þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½ � 3ѽC8.þ� Åà ÝZÃÅÊ/ "3íæÜÝôÞE½[ë-ç� ÅÃß¿�� æ½G9�çE½�¿.Êtà ¼' *ÚܽG9�çE½%æÂÊèæ0ÃÅ¿� ÅÀ�ÁÃxÝ�¼G " �3Ѽ�æÜÝZ½�¿¢ë.ÃÅ¿��íÀ�Úèë-½�ÚH6íÿ­ÞE½ x¼%ÊtÊܽ�Ú ÀÁþEÊtÃßÄÆÃ"�%¼%ÊtÃßÀ�¿ Ãxæ�ÝZÀÁ¿-ÊÜÚK¼GÃß¿¢ë-à Ý�¼GÊܽ%ëwãdÀ�Ú!æ_½G9�çE½�¿.ÊtÃx¼G ÇæÂÊtÚܽ%¼GÄäæNÀGã~,)ÚtÃßÊt½íÚt½O9êçE½[æÂÊKæÙæ½�Ú/1-à ÝZ½%ë � 3ë-à æ4.àæ�,)ÃßÊtÞEÀÁçEÊ­ÊÜÞE½ ¼ � Ã� ÅÃÅÊ=3ÙÊtÀ5þEÚt½ � ç0�F½�Úc,)ÚÜÃÅÊܽ)Út½G9�çE½%æ_Ê­ëà¼GÊK¼.×E¼Áæ ÃÅÊ]þEÚÜÀ.ë-ç¢ÝZ½[æ­¼G¿L¼' ßÄÆÀ�æ_Ê]þ¢¼GÊÜÞEÀ ßÀ��ÃßÈ

Page 100: Aggressive Centralized and Distributed Scheduling ofDisk Requests

� å

Scheduling Algorithmõ0

10

20

30

40

50

60M

ean

Res

pons

e T

ime

(ms)

öCQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û ¼êükj¾½%¼%¿¾ý)½%æ_þbÀÁ¿¢æ½òÿ­ÃÅÄƽ

Scheduling Algorithmõ0

50

100

150

200

250

App

licat

ion

Run

Tim

e (s

ec)

� CQ = 1÷CQ = 2÷CQ = 4÷CQ = 16÷

Preseekø Fullù

SPTF.CW.SSRú SPCTF.CW.SSRú C-LOOK.CW.SSR C-LOOK.CW.SSR

û�� ü+� þEþ� ÅÃxÝÛ¼GÊtÃßÀ�¿íý)çE¿ ÿ­ÃÅÄL½

Ë)ÌDÍ��¯Î%ÏwÐFÒÅÓ¢¦�ÕÆñ]ó���RTSKÖEUJUK�¾é.ÝKÞE½%ë-ç� ÅÃÅ¿��?�� ���À�ÚÜÃÅÊÜÞEÄ á2½�Ú_ãdÀ�ÚÜÄí¼G¿¢Ý�½�ãdÀ�Ú�� Ã��F½�Úܽ�¿.ÊÆÉ]À�ÄÆÄí¼%¿¢ë�`çE½ÛçE½%�n½�¿���ÊÜÞ¢æ

Page 101: Aggressive Centralized and Distributed Scheduling ofDisk Requests

��

Ý�¼G " "3 ÃÅ¿-ãd½�ÚÜÃÅÀÁÚ�Út½G9�çE½%æ_Ê2ÀÁÚKë-½�ÚÜÃÅ¿���6��� æÂÀà×GÊÜÞE½)æ_½C Ž%Ý�Êt½%ë0ÃÅÄLþ� Ž�Ä!½�¿�Êè¼GÊtÃßÀ�¿0À%ã¢ÊtÞà½)æ½O9êçE½Û¿-ÊÜÃx¼' .æÜÝôÞà½%ë-ç� ßÃÅ¿��À�þàÊtÃÅÄLÃ"�%¼%ÊtÃÅÀÁ¿ÆÃxæ � ½�ÊÜÊt½�Ú`æ_çEÃÅÊܽ%ë�ÊÜÀ éEéêÿN* ÊtÞî¼G¿5�;|V|�} ÀÁÚ#ý éEÉ+��� û @06^�êü�6

r(¿ æ_ÃÅÄ!ç� x¼%ÊtÃßÀ�¿¢æEç¢æ_ÃÅ¿��`ë-à æ4.àæ�,)ÃÅÊÜÞV*"É+*]é0Ý�À�ÄÆÄí¼%¿¢ë!9êçE½ÛçE½�ÃÅ¿��E×%æÂÞàÀ�ÚtÊܽ�Ú¯ÝZÀÁÄÆÄí¼G¿îëN9êçE½ÛçE½� Ž�¿��ÁÊtÞ¢æû ½Q6���6ß×�CB & þ¢½�¿îë-ÃÅ¿�� Út½G9�çE½%æ_ÊKæ�þb½ÛÚ*ë-à æ4.¢ünÚܽ%æÂç� ÅʯÃÅ¿ � ½�ÊtÊܽ�Ú2þ¢½�Ú_ãdÀ�ÚÜÄí¼G¿¢Ý�½\6*é�ÞEÀ�ÚÜÊ*À�¿àÈ(ë-à æ4.%9�çE½�çE½%毼' � ÅÀG,¼NÞàÀ�æÂÊÜÈ � ¼�æ½[ë¾ætÝKÞE½%ë.ç� Ž�Ú�ÊtÀ�Äí¼%ÃÅ¿.ÊK¼GÃß¿�ÊtÞE½!�¢½C8.à � Ã� ÅÃÅÊ=35ÊtÀòë03.¿¢¼GÄÆà Ý�¼' � "3ÙÚt½�ÀÁÚKë-½�Ú]ÊÜÞE½0Äí¼'z_ÀÁÚtÃßÊ43ÙÀGã¯ÊÜÞE½þ¢½�¿¢ë-Ãß¿��¾ÚܽG9�çE½%æÂÊèæZ×v,)ÞEÃ� Ž!½C8-þ� ÅÀ�ÃßÊtÃß¿��íæÂÀÁÄƽ!ÀGã)ÊÜÞE½ÆÃß¿-Êܽ�ÚtÈdÚt½G9�çE½%æ_Ê0Ý�À�¿¢ÝZçàÚtÚt½Û¿¢ÝW3 ¼C1Á¼GÃ" ¼ � ߽Ƽ%Ê ½%¼ÁÝôÞë-à æ4.T6*r(Ê*Ãxæ� ßÃ".�½C �30ÊtÞ¢¼%Ê­ÊÜÞE½)À�þEÊÜÃÅÄí¼G �9�çE½�çE½N ß½�¿���ÊÜÞ21Á¼%ÚtÃŽ[æ;,)ÃÅÊÜÞ�ÊÜÞE½0ÝÛ¼�ÝKÞE½`ÝZÀ�¿F]���çEÚè¼GÊÜÃÅÀ�¿�6�ÿ ÀG,­½C1�½�ÚÛ×æÂçîÝôÞ ¼!æÂÊtçîë03ÆÃxæ � ½C3�ÀÁ¿¢ëÆÊtÞE½ÙæÜÝZÀ�þ¢½ À%ã]ÊtÞàÃxæ)ë-à ætæ½ÛÚtÊK¼%ÊtÃßÀ�¿v6

�I�J� ���+�5���?�?�G�G�5� �����k� �;�5�\�:�c� �V�k�H�2�  ����2� ¡s¢n£q��¤-��¥ �¦�?�¡+§¨���H�V�©¥

ÿ­ÞEÃxæ¯æ½[ÝZÊtÃßÀ�¿ ½H8E¼%ÄÆÃÅ¿E½[æbÊtÞ཭æ=3Eæ_Êt½�Ä þ¢½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½�½W�F½%ÝZÊKæ�ÀGãb¼�ëEë-Ãß¿��5æ=3Eæ_Êt½�ÄÆÈ� ŽH1�½C C..¿EÀG,N Ž%ë0�Á½­ÊÜÀÞEÀ æÂÊtÈ � ¼Áæ½%ëÑÝZ½Û¿-ÊÜÚK¼' ßÃ"��½[ë�æÜÝôÞE½[ë-ç� ÅÃß¿��!¼' ���ÀÁÚtÃÅÊÜÞEÄíæ�6�ª³ÃÅÊtÞàÀ�çEÊ`½C8.þ� Åà ÝZÃÅÊ�..¿EÀG,N Ž%ë0�Á½5ÀGã]ÚܽG9êçà½%æÂÊ)þEÚÜÃÅÀÁÚtÃÅÈÊtÃß½%æ*À�ÚÇÊtÞE½`ÃÅÄÆþî¼�ÝZÊ*À%ã¯ÃÅ¿¢ë.Ã"1.Ãxë-碼G EÚt½O9êçE½[æÂÊKæ]À�¿Æþ¢½�Ú_ãdÀ�ÚÜÄí¼G¿¢Ý�½`¼G¿¢ëbsÛÀ�Ú)ÚܽC Åà ¼ � Ã� ÅÃÅÊ=3V��À ¼' æZ×E¼ÙætÝKÞE½%ë-ç� Ž�ÚÝ�¼%¿|ÀÁ¿� "3 ¼GÊtÊܽ�ÄÆþEÊ`ÊtÀLþEÚt½C1�½Û¿-Ê`ÊtÞE½!æ_ÊK¼%ÚE1Á¼GÊÜÃÅÀ�¿ ÀGã`Ý�ÚtÃÅÊÜÃxÝ�¼G �Út½G9�çE½%æ_ÊKæ � 3¾ÄLÃÅ¿EÃßÄÆÃ<��Ã4¿���ÊtÞE½�Úܽ%æÂþ¢ÀÁ¿¢æ½ÊtÃßÄƽ!1�¼%Útà ¼G¿¢ÝZ½Q6 é�çîÝôÞíÃxæ­ÊÜÞE½ÙÝ�¼�æ_½0ãdÀ�Ú ætÝKÞE½%ë-ç� ßÃÅ¿��ÙÊtÞE½Ùë-à æ4.ÆÚܽG9�çE½%æÂÊ)ÊÜÚK¼ÁÝZ½%æ­ãdÚtÀ�Ä ÿ0á ¼%¿¢ë���«­É!6FrDã¼Gþàþ� Åà Ý�¼GÊÜÃÅÀ�¿îæ­À�Úk]¬ Ž5æ=3Eæ_Êt½�Äíæ]þ¢¼�æÜæ)æ43àæÂÊܽ�ÄÆÈ� ŽC1�½C .ÃÅ¿.ãdÀ�ÚtÄä¼GÊtÃßÀ�¿ÆÊÜÀ!¼�ætÝKÞE½%ë-ç� Ž�ÚÛ×êÃßÊ)Ý�¼%¿L��Ã"1�½`þEÚÜÃÅÀ�ÚÜÃÅÊ=3ÊtÀ5ÊÜÞE½)ÄÆÀ�æ_Ê�­tÃßÄÆþ¢À�ÚÜÊK¼G¿.ÊJ®0ÚܽG9êçà½%æÂÊèæW6*ÿ­Þ཭ãdç� " ¢æ=3Eæ_Êt½�Ä ÊtÚè¼�ÝZ½%æ û ÊK¼'.�½Û¿ ãdÚtÀ�Ä ÊÜÞE½!�NÉÇý#,­À�Ú/.Eæ_ÊK¼%ÊtÃÅÀÁ¿nüÃxë.½�¿-ÊÜà ã�3I,)ÞàÃxÝKÞ¾Út½O9êçE½[æÂÊKæ ¼GÚt½�ÊÜÃÅÄƽÛÈ(ÝZÚÜÃÅÊÜÃxÝ�¼' �¼%¿¢ëÑÊtÃÅÄL½�ȯ ßÃÅÄ�ÃßÊt½%ën×à¼' � ÅÀG,)ÃÅ¿��L¼íætÝKÞE½%ë-ç� Ž�Ú)ÊÜÀÆÀ�þEÊÜÃÅÄÆÃ���½ãdÀ�Ú`æ=3Eæ_Êt½�Ä þb½ÛÚÂãdÀ�ÚÜÄí¼G¿îÝZ½\6*r(¿Æ½ÛÃÅÊtÞà½�Ú)Ý�¼Áæ½�×¢¼�æÜÝôÞà½%ë-ç� ß½�Ú)æ_ÞEÀ�ç� ëíæÂÊtÃ� " Fç¢æ½5ÊtÞའæ_ç � æ=3Eæ_Êt½�ÄìÞî¼GÚKëF,)¼GÚܽ½Z«äÝZÃŽۿ-Ê/ "3 û�� 3L½C8-þ� ÅÀ�ÃßÊtÃß¿�� Þ¢¼%ÚKë0,k¼GÚܽ�È(æ_þ¢½%ÝZÃ�]bÝ�..¿EÀG,N Ž%ë0�Á½�üJ6

`!a{°!a/b ±²x=w�³µ´Z¶¸·�f!¶;wF¹Zº-j�h�tv¶;w*2Ã"�ÁçEÚt½[æ ( 6ÅØ ) B ( 6A�.Ø ÃÅ¿ æ_½%ÝZÊtÃßÀ�¿ ( 6ÅØD6A�!æÂÞEÀG, ÊtÞE½5Äƽ%¼%¿ÆÚt½[æÂþ¢À�¿¢æ_½ ÊÜÃÅÄƽ%æ]¼%¿¢ë¾ÝZÀ�½�«íÝZÃß½�¿.ÊKæ*ÀGã�1Á¼%ÚtÃÅÈ

¼GÊÜÃÅÀÁ¿wãdÀÁÚV�Né.á]ÿN* û ) ü ¼G¿¢ë��Né.á­ÉÇÿN* û ) ü ætÝKÞE½%ë.ç� ÅÃß¿���À%ã)ÊÜÞE½!æÂÃ�8?»0á ¼G¿¢ë���«­É ÊÜÚK¼ÁÝZ½%æW6òÿ­ÞE½!¼'�Á½�Èæ½ۿ¢æÂÃßÊtÃ"1�½ é.á]ÿN*2È � ¼�æ½[ë ¼' ���ÀÁÚtÃÅÊÜÞEÄíæÙ¼GÚt½L1.Ãxæ_à � �3|ÄÆÀÁÚt½ÆÚܽ%æÂà æÂÊè¼G¿.Ê�ÊtÀ æÂÊè¼GÚ/1�¼%ÊtÃßÀ�¿ ÊÜÞ¢¼G¿ é.á]ÿN* ¼G¿¢ëé.á­ÉÇÿN*c6v»`À',ǽC1�½�ÚÛ×qÉ]ȼ�;|V|�} þEÚtÀG1.Ãxë-½%æ)½G9�çEÃ"1Á¼G Ž�¿.Ê û À�ÚÙæ4 ßÃ"�ÁÞ-Ê/ "3 æÂçEþ¢½�ÚÜÃÅÀÁÚZü`æ_ÊK¼GÚ/1Á¼GÊtÃßÀ�¿ Úܽ%æÂà æÂÊè¼G¿¢ÝZ½ãdÀ�Ú%,­ÀÁÚE.F ÅÀ�¼ÁëEæ0À�¿ ÊÜÞE½-1�½�ÚE3 ½%ë0��½!ÀGã æܼGÊÜçEÚK¼%ÊtÃÅÀÁ¿v6Iª³ÞE½�¿ ÊtÞà½Æ¼G��½�È�æ½�¿îæÂÃÅÊÜÃ"1�½L¼' ���À�ÚÜÃÅÊÜÞEÄíæ � ½C�ÁÃÅ¿ ÊÜÀæt¼%ÊtçEÚè¼GÊܽ�×2ÊÜÞE½�ÃÅÚ � ½ÛÞ¢¼C1-ÃßÀ�ÚÙæÂÊè¼GÚtÊèæ0ÊtÀ¾Úܽ%æ½ÛÄ � ß½%*"É+* é û ,)ÃÅÊÜÞ ¼ÆÚt½[æÂç� ßÊtÃÅ¿��¾æ_Þ¢¼GÚÜþ|Ãß¿¢ÝZÚܽ%¼�æ_½�Ãß¿ÑÄƽ%¼G¿Út½[æÂþ¢À�¿¢æ_½�ÊtÃßÄƽ%æôü�6­ÿ­ÞàÃxæ)Ãxæ)ÄÆÀ�æ_ÊN1-à æÂà � ŽV,)ÃÅÊÜÞ¾ÊtÞà½2�T½C¾"¿HÀ��n×+ÁNS/Â-Ö�Sô×¢¼%¿¢ëM0Ö¼REó\SJÃnÊÜÚK¼�Ý�½%æW6)ÿ­Þà½�æ½۽C.-ÈÚt½[ë-ç¢ÝZÃß¿��Ù¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæ û ½[æÂþ¢½%ÝZà ¼' " �3�É]ȼ�;|V|�} ü"æt¼GÊÜçEÚK¼%Êt½0Ä!ç¢ÝKÞ ÄÆÀÁÚt½N�ÁÚK¼�ë.碼' � "3\6X*îÀÁÚ)æ_À�Äƽ`æ=3Eæ_Êt½�Äíæ�×ÊtÞàÃxæ­Ê=3-þ¢½5ÀGãX��Úè¼�ÝZ½�ãdç� ¯ë-½C�ÁÚK¼�ëà¼GÊtÃßÀ�¿Ñà æ)¼' xæ_À!¼G¿ ÃÅÄÆþ¢À�ÚÜÊK¼%¿-ÊN�ÁÀ�¼' ¼6Ä­½%Ý�¼%ç¢æ½��Néêá ÿN* û ) ü ë-À�½%æÆ¿EÀ�ÊL½W�F½%ÝZÊtÃ�1�½C "3 çEÊtÃ� ÅÃ"�Û½ ÊÜÞE½ÑÀ�¿àÈ � À�¼%ÚKë ÝÛ¼�ÝKÞE½�×)ÃÅÊLæt¼%ÊtçEÚè¼GÊt½[æäÄLÀ�Út½

9�çEÃxÝJ.0 �35ÊtÞ¢¼%¿Æ½�ÃÅÊÜÞE½�Ú]ÊtÞà½0æ_½�½C..ÈDÚܽ%ë-ç¢ÝZÃß¿��5¼G "��ÀÁÚtÃßÊtÞEÄíæ*ÀÁÚN�Né.á­ÉÇÿN* û ) ü�6�» ÀG,­½C1�½�ÚÛ×GÃßÊ]þEÚtÀG1.Ãxë-½%æ]æ_çEþ¢½�ÈÚtÃßÀ�Ú`þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½5ÀG1�½�Ú)ÊtÞE½òæ½�½H.-ÈdÚt½%ë.ç¢ÝZÃÅ¿��!¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæ ãdÀ�Ú æÂÀÁÄƽÙæÂç � È�æt¼%ÊtçEÚè¼GÊÜÃÅÀ�¿�,­ÀÁÚE.F ÅÀ ¼�ëEæ�6�*EÀÁÚ½C8à¼GÄÆþ� Ž�×Å]¬��çEÚܽ ( 6A�-ØÛ¼ÑæÂÞEÀG,`æ5ÊtÞ¢¼%Ê:�Né.á]ÿN* û ) ü Þ¢¼�æ5çEþ ÊtÀ Ø �\7 ßÀ',ǽ�Ú0Äƽ[¼G¿ Út½%æ_þbÀÁ¿¢æ½LÊtÃÅÄL½%æ Ãß¿ÊtÞà½y@F6 & È{@F6 P ÚK¼G¿���½ À%ã]æÜÝ�¼' ßÃÅ¿���ã�¼�Ý�ÊtÀ�Úèæ ãdÀ�Ú`ÊtÞE½: Ö{Ràó\S_âÊtÚè¼�ÝZ½\6�� ÅÊÜÞEÀ�ç���Þ5�Né.á­ÉÇÿN* û ) ük¼' ",k¼C3Eæ]Þ¢¼�æ � ½�ÊtÊܽ�Ú)æ_ÊK¼GÚ/1Á¼GÊtÃßÀ�¿ Út½%æ_ÃxæÂÊè¼G¿¢Ý�½NÊÜÞ¢¼G¿Ñé.á­ÉÇÿN*­×EÊÜÞE½5Út½C ¼GÊÜÃ"1�½

þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½0À%ã*ÊÜÞE½%æ_½0Ê=,­À�¼G "�ÁÀ�ÚtÃßÊtÞEÄäæ û ¼Áæ ÄL½%¼�æ_çEÚt½%ë � 3�Äƽ[¼G¿ÆÚܽ%æÂþ¢À�¿îæ½5ÊtÃßÄƽ%æôü�ë-½Ûþb½Û¿¢ëEæ­À�¿íÊÜÞE½ÃÅ¿îë-Ã"1.Ãxë-çî¼' F,­À�Ú/.0 ßÀ�¼Áë�6]r(¿!æÂÀ�ÄL½`Ý�¼�æ_½%æZ×�ÊtÞà½`¼'��Ãß¿��0ã�¼�ÝZÊÜÀ�Ú]ÃÅÄLþEÚtÀG1�½%æ � À�ÊÜÞíæÂÊè¼GÚ/1�¼%ÊtÃßÀ�¿!Út½%æ_ÃxæÂÊè¼G¿¢Ý�½`¼G¿¢ëþ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½ � 3�Ää¼GÃÅ¿.ÊK¼%ÃÅ¿EÃß¿��5ÊtÞE½ À�ÚKë.½�ÚtÃß¿�� À%ã�æ½G9�çE½�¿.Êtà ¼' ¢Út½G9�çE½%æ_ÊKæ*ÃxæÜæÂçE½[ë�ÃÅ¿I ßÀ�ÁÃxÝ�¼G " "3!¼ÁætÝZ½Û¿¢ë-ÃÅ¿��

Page 102: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�P

À�Úèë-½�ÚH6Æ�Néêá ÿN* û ) üò¼G¿îëÆ�Né.á­ÉÇÿN* û ) üÙþEÚtÀG1.Ãxë-½ � ½ÛÊtÊt½ÛÚ�þ¢½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½LÊtÞ¢¼%¿®é.á]ÿN* ¼%¿¢ë éêákÉÇÿN*Ç×Út½[æÂþ¢½%ÝZÊÜÃ"1�½C �3�×GãdÀ�Ú`ÄÆÀ æÂÊ)æ_ç � È�æt¼%ÊtçEÚè¼GÊtÃßÀ�¿ ñ­ÖJÇ�Ç4ó�×NÁNS/Â-Ö�SK×E¼G¿îëÈ0Ö¼REó\SJÃ�,­ÀÁÚE.F ÅÀ ¼�ëEæ�6

`!a{°!a{° É�f!u=uÈe+l!w0¹�¶�g º-j�h�tv¶¸wÿ­ÞEÃxæ�æ½%ÝZÊÜÃÅÀÁ¿�þEÚt½%æ_½�¿.ÊKæ2þ¢½�Ú_ãdÀ�ÚtÄä¼G¿¢ÝZ½këE¼GÊè¼ ãdÀ�Ú]æÜÝôÞE½[ë-ç� ÅÃß¿�� ¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæqçîæÂÃÅ¿��Nþ¢½�ÚÜÈDÚܽG9�çE½%æÂÊ�þEÚtÃßÀ�ÚtÈ

ÃÅÊ=3ÆÃß¿-ãdÀ�ÚÜÄí¼GÊÜÃÅÀÁ¿v6 é�½%Ý�ÊtÃÅÀÁ¿ ( 6ÅØD6 � ë-½�ÄÆÀÁ¿¢æÂÊÜÚK¼%Êt½%æ)ÊtÞ¢¼%Ê0Ý�À�¿¢Ý�¼%Êt½�¿î¼GÊtÃßÀ�¿ÑÀ%ãÇæ½G9�çE½�¿.Êtà ¼' v,)ÚÜÃÅÊt½5ÚܽG9êçà½%æÂÊèæÃxæ]ÊtÞE½`À�¿� "3!½W�F½%ÝZÊtÃ�1�½`æ½G9�çE½�¿.Êtà ¼' ¢æ_ÊtÚܽ%¼GÄ À�þEÊÜÃÅÄÆÃ��%¼GÊÜÃÅÀÁ¿ ãdÀ�Ú)æÜÝôÞà½%ë-ç� ßÃÅ¿��5ÊtÞའãdç� � Fæ43àæÂÊt½ÛÄ ÊÜÚK¼�Ý�½%æW6X�� " ÀGã"ÊtÞE½ÙætÝKÞE½%ë.ç� Ž�Úèæ Ãß¿ ÊÜÞEÃxæ)æ_½%ÝZÊÜÃÅÀ�¿íÊÜÞE½�Út½�ãdÀ�Út½ ç¢æ½ÙÝZÀÁ¿¢Ý�¼GÊܽ�¿¢¼%ÊtÃÅÀÁ¿¾À%ãÇæ½G9�çE½�¿.Êtà ¼' T,)ÚtÃÅÊܽ%æW6

Ê�Ë'̯ÏFÍ;�¸ÎDÌ�ϯÍMÐ�ÑZÒcӢ͢Ì�Ë\Ô�ÎcÕ:Î�ÓvË5÷[Ö5�;×�Ð]Ï-Î*2Ã"�ÁçEÚt½ ( 6 ( @ þEÚܽ%æ½ۿ-ÊèæqÊÜÞE½)Äƽ%¼%¿NÚܽ%æÂþ¢ÀÁ¿¢æ½)ÊÜÃÅÄƽ%æ�¼%¿¢ë Äƽ%¼%¿5¿EÀ�¿EÈ�ÝZÀÁÄÆþEçEÊܽ­ÊtÃßÄƽ%æEãdÀ�Ú��\�Z**É+* é¢×

��� É]È{�;|V|~}�×�¼%¿¢ëV��� éEé.ÿN*¾æÜÝôÞà½%ë-ç� ßÃÅ¿��ÇÀGãàÊtÞE½N�TØD��%Ù0Ö��c,­À�Ú/.0 ßÀ�¼ÁëEæW6�ÿ­ÞE½+��� ¼G "�ÁÀ�ÚtÃßÊtÞEÄäæn¼' �,)¼C3àæ��Ã�1�½0þEÚÜÃÅÀ�ÚÜÃÅÊ=3!ÊtÀ!ÊtÃÅÄL½�È(Ý�ÚtÃÅÊÜÃßÝ�¼' ¢¼%¿¢ë ÊÜÃÅÄƽÛȯ ßÃÅÄ!à Êܽ%ë Út½O9êçE½[æÂÊKæ û æ½�½Ùæ_½%ÝZÊtÃßÀ�¿ & 6 � 6A�êü�6­ÿ­Þà½%æ½ټ' ���ÀÁÚtÃÅÊÜÞEÄíæÊtÞà½�Út½ZãdÀÁÚt½�Þ¢¼C1�½!¼ÆÊt½Û¿¢ë-½�¿¢Ý�3¾ÊtÀ æ_ÊK¼GÚ/1�½�ÊÜÃÅÄƽÛÈD¿EÀÁ¿¢ÝZÚÜÃÅÊtà Ý�¼' �ÚܽG9�çE½%æÂÊèæ ãdÀ�ÚÙ¼G " � çàÊNÊÜÞE½- ÅÃ"�ÁÞ-Êܽ%æÂÊ~,­À�Ú/.-È ÅÀ ¼�ëEæ�6�*2Ã���çEÚܽ ( 6 ( Ø�ë-à æÂþ� ¼O3àæ)ÊtÞE½ÙÄƽ%¼G¿íÚܽ%æÂþ¢À�¿îæ½�ÊtÃßÄƽ%æ]Äƽ%¼�æ_çEÚt½[ëLãdÀÁÚ0ÊtÞའÊtÞàÚt½�½5Út½O9êçE½[æÂÊ ÝW x¼Áætæ½[æ,)ÞE½�¿ ÊtÞà½!ætÝKÞE½%ë-ç� ß½�Ú`ç¢æ½%æ5¼L��� É]ȼ�;|�|~}â¼' ���ÀÁÚtÃÅÊÜÞEÄ?65ÿ­ÞE½Lë-Ã<�n½ÛÚt½�¿¢Ý�½ ÃÅ¿ÑÄL½%¼G¿ÑÚܽ%æÂþ¢À�¿îæ½!ÊtÃÅÄL½%æ� ½�Ê=,­½�½Û¿ÆÊtÞE½5ÚܽG9êçà½%æÂÊ`ÝW ¼�æÜæ½%æ­Ãß¿¢ÝZÚt½[¼�æ½[æc,)ÃÅÊtÞíÊÜÞE½V,­À�Ú/.0 ßÀ�¼Áë ÃÅ¿.Êt½Û¿¢æÂÃßÊ43Q6Äc3#��Ã"1.ÃÅ¿��ÑþEÚtÃßÀ�ÚtÃßÊ=3 ÊtÀ ÚܽG9�çE½%æÂÊèæ ÀÁ¿Æ,)ÞEà ÝôÞ ÊtÞE½ ¼GþEþ� ÅÃxÝÛ¼GÊtÃßÀ�¿ ¼G¿îë[]� Ž æ43àæÂÊt½ÛÄ þEÚtÀ.Ý�½%ætæ_½%æƼGÚܽ

,)¼%ÃÅÊÜÃÅ¿��à×�ÊtÞE½Ú��� ¼G "�ÁÀ�ÚtÃßÊtÞEÄäæqþEÚÜÀ.ë-ç¢ÝZ½N ßÀG,­½�Ú¯Äƽ%¼%¿N¿àÀ�¿EÈ�ÝZÀ�ÄLþEçEÊt½)ÊÜÃÅÄƽ[æW6v*2Ã���çEÚܽ ( 6 ( @ � æ_ÞEÀG,`æ*ÊtÞ¢¼%ÊÊtÞà½0Äƽ%¼%¿�¿EÀ�¿EÈ�ÝZÀÁÄÆþEçEÊܽ ÊÜÃÅÄƽ%æ�ãdÀ�Ú)ÊtÞའ& ÈDç¢æ_½�Ú`¼G¿îë � Èdç¢æ½ÛÚc,­ÀÁÚE.F ÅÀ ¼�ëEæ)¼%Út½5¼%þEþEÚtÀG8.ÃÅÄí¼%Êt½C �3 �\7 ¼G¿¢ëØ )\7 ÅÀG,ǽ�Ú�ׯÚt½%æ_þb½[ÝZÊtÃ�1�½C "3�×¢ãdÀ�Ú ÊÜÞE½íæ_½�½C..ÈDÚܽ%ë-ç¢ÝZÃß¿��?�\� ¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæW6Ñÿ­Þà½íë-Ã��F½�Úܽ�¿¢ÝZ½ � ½�Ê=,­½�½Û¿|ÊÜÞE½þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½�À%ã)ÊtÞà½I**É+* é¢×2É]ȼ�;|V|~} ׯ¼%¿¢ë éEé.ÿN* ¼' ���ÀÁÚtÃÅÊÜÞEÄíæ0ë.ÃÅÄÆÃß¿EÃxæ_ÞE½%æ)ÊtÀL Ž%æÜæ0ÊtÞ¢¼%¿³Ø 7 ãdÀÁÚ��� æÜÝôÞà½%ë-ç� ßÃÅ¿���6*2Ã"�ÁçEÚt½ ( 6 ( � æÂÞàÀ',`æ�ÊtÞའÄL½%¼G¿ Úܽ%æÂþ¢ÀÁ¿¢æ½ ÊtÃÅÄL½%æ5¼G¿¢ë ¼GþEþ� ßÃxÝ�¼%ÊtÃßÀ�¿ ÚtçE¿ ÊtÃßÄƽ%æ ãdÀ�Ú��vÄN� È � ¼�æ_½%ë

��� æÜÝôÞE½[ë-ç� ÅÃß¿��0À%ã¯ÊtÞE½íñ]ó\Û�RTSKÖEUJU¸,­ÀÁÚE.F ÅÀ�¼Áë�6�ª³ÞEÃ� Ž)Äƽ%¼%¿�Úܽ%æÂþ¢ÀÁ¿¢æ½0ÊÜÃÅÄƽ[æ2ÃÅ¿¢Ý�Út½%¼Áæ½)ÀG1�½�ÚǼG¿ÆÀÁÚKë-½ÛÚÀGã"Äí¼'�Á¿EÃÅÊÜç¢ë-½�×EÚÜçE¿¾ÊÜÃÅÄƽ%æ)ë.ÚtÀ�þ æ4 ßÃ"��Þ.ÊE �3�ãdÀ�Ú~��� ætÝKÞE½%ë.ç� ÅÃß¿���ÀGã+**É+* é û �06 P�7 üK×�É]È{�;|V|~} û @06^� 7 üK×¼G¿îë|éEé.ÿN* û @F6 �\7 ü�60ÿ­ÞEà æ�,­ÀÁÚE.F ÅÀ�¼Áë¾ÝZÀÁ¿¢æÂà æÂÊèæ ÀGãkæ½Ûþ¢¼GÚè¼GÊt½!æ_½G9�çE½�¿.ÊtÃx¼G ¯æÂÊÜÚt½%¼%Äíæ À%ãÇÚt½%¼Áë¾¼G¿îëÈ,)ÚÜÃÅÊt½Út½O9êçE½[æÂÊKæÙætÝ�¼%ÊtÊܽ�Út½%ë ¼�Ý�ÚtÀ�æÜæ ÊtÞE½äë-Ãxæ=.�6 ÿ­ÞE½ÆÚܽ%¼�ë Út½O9êçE½[æÂÊKæ5¼%Út½ÆÄÆÀ æÂÊ/ "3ÑÊtÃßÄƽ�È� ÅÃßÄ�Ã4Êt½[ë û ,)ÃßÊtÞ æ_À�ÄƽÊtÃßÄƽ�È�ÝZÚtÃßÊtà ÝZ¼G nÚt½O9êçE½[æÂÊKæKüK×�,)ÞEÃ" ß½ ÊÜÞE½y,)ÚÜÃÅÊt½ÙÚt½G9�çE½%æ_ÊKæ`¼GÚܽ!¼' ÅÄLÀ�æÂÊ ¼' � 2ÊÜÃÅÄƽÛÈD¿EÀÁ¿¢ÝZÚÜÃÅÊtà Ý�¼' ¼6sÜ`Ã�1-Ãß¿���þàÚtÃÅÈÀ�ÚÜÃÅÊ=3ÑÊtÀ ¼ÆãdÚK¼ÁÝZÊtÃßÀ�¿ À%ã0ÊÜÞE½�ÊÜÀ�Êè¼' `æ½ÛÊ ÀGã`ÚܽG9�çE½%æÂÊèæ ë-½�ãd½%¼GÊèæNÄ!ç¢ÝôÞÑÀ%ã`ÊtÞE½äæ½�½C..ÈdÚt½%ë-çîÝZÃÅ¿�� � ½�Þ¢¼C1.ÃÅÀÁÚÀGãÇÉ]ȼ�;|�|~} ¼%¿¢ëwéEéêÿN*c6�*EÀ�Ú)½H8E¼%ÄÆþ� Ž ×-æ=,)ÃÅÊèÝôÞEÃß¿��NãdÚÜÀ�Ä É]ȼ�;|V|~}¦64É�ª ÊtÀ-�\� É]ȼ�;|V|�}:64É�ª ÃÅ¿EÈÝZÚܽ%¼�æ_½%æNÊÜÞE½ÆÄƽ%¼%¿ æ½۽C. ë-Ãxæ_ÊK¼%¿¢ÝZ½�ãdÚÜÀ�Ä ØH� ) ÝW3F ÅÃß¿¢ë-½�Úèæ ÊÜÀ ()D� ÝW3F ÅÃß¿¢ë-½�ÚèæW6 ÿ­ÞE½ÆÄƽ[¼G¿ æ½�½C. ÊtÃßÄƽÄÆÀÁÚt½ ÊÜÞ¢¼G¿ ë.À�ç � ß½%æ5¼�æ0¼ÆÚܽ%æÂç� ßÊ�×nÃß¿¢ÝZÚܽ%¼�æ_ÃÅ¿���ãdÚtÀÁÄ � 6 (( Äíæ)ÊtÀ � 6 &\� ÄäæW6V**É+* é¢×�,)ÞEÃxÝKÞ ë-À�½%æ0¿EÀÁʼGÊÜÊt½�ÄLþEÊ­ÊÜÀ�ÄÆÃß¿EÃÅÄ!Ã"��½`æ½۽C.íë-½C ¼C3Eæ�× � ½�¿E½W]îÊKæ­ÊtÞà½NÄLÀ�æÂÊ­ãdÚÜÀ�ĵ�\� ætÝKÞE½%ë-ç� ÅÃÅ¿���6

Ê�Ë'̯ÏFÍ;�¸ÎDÌ�ϯÍÈÝ!Ì�ÞG̳Ëv�¸Î¯ÎNß5Ï;Ó\Ý-ÎDÏFͯÍbÏ*2Ã"�ÁçEÚt½ ( 6 (� ë-à æÂþ� ¼O3àæ0þ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½!ëE¼%ÊK¼äãdÀÁÚ%���ìé.á]ÿN* ¼G¿¢ëq���ìé.á­ÉÇÿN* æÜÝôÞà½%ë-ç� ßÃÅ¿��ÆÀ%ã)ÊÜÞE½

�TØD��%Ù0Ö���,­ÀÁÚE.F ÅÀ�¼ÁëEæW6]ÿ­Þའ� ½ÛÞ¢¼C1-ÃßÀ�Ú*À%ãnÊÜÞE½%æ_½`¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæqà æ*æÂÃßÄÆÃ" ¼GÚFÊtÀ5ÊtÞE½ � ½�Þ¢¼C1-ÃßÀ�Ú*À%ãFÊtÞE½!�vÄN� È� ¼Áæ½%ëà�\� ¼' "�ÁÀ�ÚÜÃÅÊtÞàÄíæW6Lá¾½%¼%¿|Úܽ%æÂþ¢ÀÁ¿¢æ½íÊtÃßÄƽ%æN��ÚÜÀ', ÚK¼%þEÃxëF "3 ¼�æ5ÊtÞE½-,­ÀÁÚE.F ÅÀ ¼�ë|Ãß¿¢ÝZÚt½[¼�æ½[æZ×;,)ÞàÃ" ŽÄƽ%¼%¿ ¿EÀ�¿EÈ�ÝZÀÁÄÆþEçEÊܽ¾ÊtÃßÄƽ%æÙë-ÚtÀÁþ � 3 çEþ ÊtÀ³Ø � 6 �\7 ×)Äí¼%ÊKÝKÞEÃÅ¿��¾ÊtÞཾþ¢½�ÚÂãdÀÁÚtÄí¼%¿¢ÝZ½ ÀGã%�\�n**É+* é�6ÿ­ÞE½�ÚܽZãdÀ�Úܽ�×�ÃÅÊ0à æ ã�¼GÚ5ÄÆÀ�Úܽ ÃßÄÆþ¢À�ÚtÊè¼G¿.Ê0ÊtÀ ½C8.þ� ÅÀÁÃÅÊ æ43àæÂÊt½ÛÄÆȯ ß½C1�½C �Ãß¿-ãdÀ�ÚÜÄí¼GÊÜÃÅÀ�¿ÑÊÜÞ¢¼G¿ ÄÆÃß¿EÃÅÄÆÃ<��½ Äƽ�ÈÝKÞ¢¼G¿Eà Ý�¼' T x¼%Êt½�¿¢Ý�ÃŽ%æ*ãdÀ�Ú ¼â�TØD��%Ù0Ö��y,­ÀÁÚE.F ÅÀ�¼Áë À%ã*çEþ ÊtÀ � ç¢æ½ÛÚKæW6

Page 103: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P @

ã ã FCFSä ä 2Q FCFSå å C-LOOK æ æ 2Q C-LOOK ç ç SSTF è è 2Q SSTF

|é0.5ê |é

1.0ê |é2.0ê |é

4.0ê |é8.0ê

|ë0

|ë100

|ë200

|ë300

|ë400

|ë500

Number of Users

Mea

n R

espo

nse

Tim

e (m

s)

ìì

ì

ì

íí

í

í

î îî

î

ï ïï

ï

ðð

ð

ð

ññ

ñ

ñ

ò¼óôXõ2ö�óC÷-ø�ö�ùGú\ö�û{üNø�ö�û{ý0þG÷Fû{ö�ÿ����Vö

� � FCFS� � 2Q FCFS� � C-LOOK � � 2Q C-LOOK � � SSTF 2Q SSTF

|é0.5ê |é

1.0ê |é2.0ê |é

4.0ê |é8.0ê

|ë0

|ë100

|ë200

|ë300

|ë400

|ë500

Number of Users

Mea

n N

on-C

ompu

te T

ime

(ms)

�� �

��

��

�� �

ò���ôXõ2ö�óC÷���þ'÷����¸þ��Vý\ú\ü=ö!ÿ�����ö������� �"!$#&%'#)(+*N�TØD��S�,.-_�./c�vÄN�10{Ä�2Áæ43%ëL���%6�5�ª �� "�7698;:=<?>)@BA�3C84DE698;@F2"GIHJ3

Page 104: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P.K

L L All RequestsM M Time-NoncriticalN N Time-LimitedO O Time-Critical

|P0.5Q

|P1.0Q

|P2.0Q

|P4.0Q

|P8.0Q

|R0

|R100|R200

|R300

|R400

|R500

|R600

|R700

Number of Users

Mea

n R

esp

on

se T

ime

(ms)

S SS

S

TT

T

T

U U U UV V V V

���E������!W#&%'#&XY*!�TØ��SE,.-��.Z��\�[5]\;|V|�}:6�5�ª^/�á_3�2"G ý�3�`Âþa69GI`43�ÿb:c@d3�` � 3íý�3G9�ef3�`g<h5� '27`?`

Page 105: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P �

FCFS C-LOOKi SSTFj 2Q FCFSk 2Q C-LOOKl 2Q SSTFjScheduling Algorithmm

0

200

400

600

800

1000

1200

Mea

n R

espo

nse

Tim

e (m

s)

n

û 2êüÚá_3�2�G¾ý�3�`_þY67Ga`43òÿb:=@d3

FCFS C-LOOKi SSTFj 2Q FCFSk 2Q C-LOOKl 2Q SSTFjScheduling Algorithmm

0

50

100

150

200

250

Appl

icat

ion

Run

Tim

e (s

ec)

o

û�� ü+� þEþ� =:'HC2"<?:c69Gíý�efG ÿb:=@p3������� ��!$#q%'#ar&*tsvu\Û�RTSw-EUJUx/y\vÄN�h0¼Ä�29`g3�z��\�%6{5�ª �� "�7698?:c<?>f@|A�3}8gDE698;@F2"GaHx3

Page 106: Aggressive Centralized and Distributed Scheduling ofDisk Requests

P�

~ ~ FCFS� � 2Q FCFS� � SPTF� � 2Q SPTF� � SPCTF� � 2Q SPCTF

|é0.5ê |é

1.0ê |é2.0ê |é

4.0ê |é8.0ê

|ë0

|ë100

|ë200

|ë300

|ë400

|ë500

Number of Users

Mea

n R

espo

nse

Tim

e (m

s)

��

��

� ��

� ��

� ��

� ��

ò¼óôXõ2ö�óC÷-ø�ö�ùGú\ö�û{üNø�ö�û{ý0þG÷Fû{ö�ÿ����Vö

� � FCFS� � 2Q FCFS� � SPTF� � 2Q SPTF� � SPCTF� � 2Q SPCTF

|é0.5ê |é

1.0ê |é2.0ê |é

4.0ê |é8.0ê

|ë0

|ë100

|ë200

|ë300

|ë400

|ë500

Number of Users

Mea

n N

on-C

ompu

te T

ime

(ms)

��

�� �

��

�� �

��

�� �

ò���ôXõ2ö�óC÷���þ'÷����¸þ��Vý\ú\ü=ö!ÿ�����ö���E�a����!�#q%'#)��*h�TØ9�)��,.-x��/b�fef�c�=0¡ ¢G)6"£��c3�z.¤73¦¥¨§ª©{5v« ¬h�c¤9698;:=<;>f@­A�3}8gDE698;@F2"GaHx3

Page 107: Aggressive Centralized and Distributed Scheduling ofDisk Requests

®"¯

° 3�HJ<;:=67G�±.© K ©³²´z.3µ`?HJ8;:=¶a3�`b>f6�£^<?>f3¦·a3}8gDE698?@¸2"GaHJ3¦6�D ° Av¹���0E¶a29`g3�z$2��=¤7698?:c<?>f@¸`b:'`b¶a3}�=6�£º<;>a2"<»6"D\vÄ�¼h0E¶a29`g3�z½2��=¤9678?:c<?>f@F`hDE678t`g:=Gf¤7�=3}0¡¾�ef3}ef3p`?Hw>f3�z.e)�=:=G)¤d6"D1<;>f3¿svu\ÛhÀ&�Á-;ÂwÂh£]698;Ã.�c6�29z&©F��:=¤7ef8?3p±.©³± ¯z.:Ä`4·f�Ä2µÅ)`Æ·a3}8gDE698;@F2"GaHx3dzf2�<w2ÇDE678t<g£b6È¥¨§ÉDEe)�=�=0EÃ�Gf6�£��=3�z.¤73d`;HÁ>)3�z.ef�c3}8w`xZ�`g>f6�£�:=Gf¤�<;>a2"<Ê<;>f3 ° Av¹���0¶a27`43�zË¥�§Ì2��=¤9678?:c<?>f@F`�2"8;3�`g�=:=¤7>.<;�=ÅÍ`4e)·Y3C8?:=678d<?6ζY67<?>Ï�y5]� ° 2�GazË\vÄ�¼h0E¶a29`g3�zË¥¨§Ð`?Hw>f3�z�ef�=:cGf¤f©¥¨§ ° Av¹���2"GIz´¥�§ ° Ab5]¹��_>a2}Ñ�312�·f·f�=:ÄH}2"<;:=67Gt8?e)GÊ<?:=@p3�`q<?>a2�<v2"8;3�6�Ñ�3}8 K�Ò �c6"£]3}8 <?>a2�Gd5v0�\�Ó¦Ó» ÊÔÕ`8?e)GÇ<;:=@d3Ö©y¬h�Ä`46Ê:=G×HJ67G.<;8w27`4<�<?6�<?>)3t`g:=Gf¤7�=3}0¡¾�ef3}ef3¦`;HÁ>)3�z.ef�c3}8w`xZf¥¨§ ° AØ5]¹��¿:'`�`g�=:=¤7>.<;�=ÅÊD¡29`g<?3}8�<;>a2"G¥¨§ ° Av¹��b© ° :cGaHJ3�<;>f3¦`?Hw>f3�z�ef�=3}8�:'`v2"�c8?3�27z.Åʤ9:cÑ.:cGf¤¦·f8?:c698?:c<gÅt<?6ª<?>f31<?:c@d3}0¡HJ8?:c<?:ÄH}2"��2�Gaz´<?:c@d3}0E�=:c@´:�<?3µz8?3µ29z´8;3�¾¨e)3�`4<Ù`JZ�29zfz�:=Gf¤�H}27HÁ>)3Ú`g3}Ga`4:c<?:cÑ.:c<4Å1Ûgea`4<]>f3}�c·a`Ü<;>f3¦`?Hw>f3�z�ef�=3}8�8?3}678wz.3}8]@´e)�=<?:c·f�=3]69ef<Ù`4<Ù2"Gaz.:cGf¤8?3µ29zÝ8;3�¾�ef3�`4<Ù`ÇÞ¡2$8w2�8?3×6�H}HJef8;8?3}GaHx39ßw©Ë¬»`à<;>f3 ° Av¹���0E¶a27`43�zÏ¥¨§á2��=¤9678?:c<?>f@F`Ê69e)<?·a3}84DE678?@ �y5]� °¶�Å�¥ Ò Z�2d>f:c¤9>f0E·a3}84DE678?@F2�GaHJ3�`?Hw>f3�z�ef�=3}8�DE698¸svu\ÛhÀ&�Á-?Âw»H}2�G�<?>f3}8;3JDE698;3Ê3}â�·f�=67:=<1¶Y67<?>Î`4Å)`4<;3}@d0E�=3}Ñ�3}�2"GIzÇ>a2�8wz.£Ø2"8?3C0�`g·Y3µHJ:{ã&HÚ:cG.DE698;@F2"<;:=69Gä©Ê�Ë'Ì !FÍ��¸Î���Ï �ÈÝ���ÞGÌË�båª��Êæå%Ó�×#×#Ô�ϸÍèçà��!���!FÍËéF��êCë�ê

��:=¤7ef8?3µ`�±�©Õ±9±}ì�±�©Õ± ® `g>f6�£½·a3}84DE678?@F2�GaHJ3v@d3}<;8?:'HC`IDE698�`4:c@´e)�'2"<;:=67Ga`Y6�Dq<;>f3yDEef�=��`gÅf`g<?3}@^<;8w29Hx3�`+eI`4:=G)¤�y5]� ° Hx69@d@F2�Gaz¦¾¨e)3}ef3�z�z.:'`gÃf` £�:=<?>�Ñ72"8;Å.:cGf¤¦@F2"â�:=@�ef@í¾¨ef3Cef3h�c3}Gf¤7<?>a`y2�GazdHJ67@d@F2�Gazt¾�ef3}ef3C:=Gf¤HJ67G.ãa¤9e)8w2"<;:=67Ga`J©Ê¹�6F@d:=G):=@�:=î}31@d3�2�G_8?3µ`4·a69Ga`g3´<;:=@d3µ`JZa2FHJ69@p@F2"GazF¾�ef3}ef3ª�=3}G)¤9<?>�6�D�<g£b6p:'`h¶a3�`g<DE698Ê�TØ7�¨ï%ÙÚ-x�.Z�2"Gazð2_HJ67@d@F2�Gaz_¾�ef3}ef3Ê�c3}Gf¤7<?>ð6"D1`g:=â�<?3}3CG¿Þ�698¦@d678?39ßØ:'`Ú69·f<;:=@F2��+DE678�svu\ÛhÀ&�w-?ÂwÂx©ñh6�£b3CÑ�3}8}Zv<?>f3ð2�·f·f�c:'H}2�<?:=67Gf0¡`4·a3�HJ:�ã&HÇ@d3C<?8?:ÄH}`Ê`4>)6"£­<;>a2"<F<?>)3_¶a3�`4<p6"Ñ�3C8w2"�c�Ú`gÅf`g<?3}@ ·a3}8gDE698?@¸2"GaHJ36�H}HJe)8w`b£�>f3}G×HJ67@d@F2�Gaz´¾�ef3}e)3}:=Gf¤ª:'`]z.:'`;2"¶f�c3�zq©v¹b>f:Ä`b:'`b¶a3�H}2�ea`43¦2Ê>f6Ö`4<?0E¶a27`43�zqZf·)8?:=678?:c<4Å�0¡`43}Ga`g:=<;:=Ñ�3`?Hw>f3�z�ef�=3}8ª�=6Ö`43�`Ê<?>f3dòa3Câ.:c¶f:=�c:=<gÅ�<?6ð8?3}678wz.3C8´·a3}Gaz�:=Gf¤ð8?3�¾�ef3�`g<w`t67GaHJ3F:=<�:'`;`4ef3�`t<;>f3}@ó<;6½2ð�y5]� °HJ67@d@F2"GIz.0�¾�ef3}e)3�zFz.:'`gÃq©ª�f698¦3}â)2"@d·f�c3�Za29`;`4ef@p3Ê<?>a2�<t2Fz.:Ä`4Ã×>a29`¦2d@F2"â�:=@Êe)@BHJ67@d@F2�Gaz_¾�ef3}ef3�=3CGf¤9<;>½6"D»<g£b6f©Îô�D»2_>f6�`g<?0E¶a29`g3�zõ¥�§­`?Hw>f3�z�ef�=3}8ª:'`;`4ef3�`t67Gf3F>f:=¤7>½·f8;:=698;:=<gÅð8?3�¾�ef3�`g<Ê2"GIzö67Gf3F�=6�£·f8;:=698;:=<gÅF8?3�¾�ef3�`g<Ú<?6¸2Çz�:'`4Ã&Za<?>f3�`;HÁ>f3µz.ef�=3C8ÚH}2�GfGf67<tHw>a2�Gf¤93Ê<;>f3Ê698Ùz.3}8Ú6�D1`43C8?Ñ�:'HJ3ª:{D]2�Gf69<;>f3}8¦>f:=¤7>·f8;:=698;:=<gÅ�8?3�¾�ef3�`g<�2"8;8?:cÑ�3�`ܶa3JDE678?3Ú<;>f3Úãa8w`g<�>f:=¤7>Ç·)8?:=678?:c<4ÅÊ8;3�¾�ef3�`4<]:'`�HJ67@d·f�c3}<?3�©ä�I67812Êz.:'`gÃd£�:=<;>f69e)<2tHx69@d@F2�Gazʾ�ef3}ef3�Z�<;>f3Ú�=6�£Ë·f8;:=678?:=<gÅÊ8;3�¾¨e)3�`4<v£b67ef�'z�Gf3}Ñ�3}8v>a2}Ñ�31¶Y3C3}Gd:'`;`4ef3µzqZf2�Gazd<?>f3»`?Hw>f3�z.e)�=3}8£b67ef�'zd¶a3ÆDE8;3}3Ú<;6´:Ä`?`4e)3Æ<;>f3ª`43�Hx69Gazd>f:c¤9>_·)8?:=678?:c<4Å�8?3µ¾¨ef3µ`4<�27`h`g6�69Gð27`÷<;>f3Úãa8w`g<1HJ69@d·)�=3}<;3�zq©ø1ù�ú1ù�û ühýÚþÿþ������������� ����?ý������� ��

¬Úzfz.:cGf¤¦2�¤93}0¡`43}GI`4:=<;:=Ñ�:=<gÅÚ<;6 ° Aܹ�� 0�¶a27`43�z�2"�c¤9678?:=<;>f@F`�:=@d·)8?6�Ñ�3�`q`g<w2�8?Ñ72"<;:=69G�8?3µ`4:'`g<w2�GaHJ3¦Þ�:¡© 3�©cZJ<;>f3`?¾�ea2�8?3�z�HJ6�3��FHJ:c3}G�<�6"D]Ñ72"8?:Ä2"<;:=69G&ßw©%ÄbÅ_Hx698?8;3�HJ<;�=Å��;£b3}:c¤9>�<?:=G)¤��d2�¤9:=G)¤Ç:cG.DE698;@F2"<;:=67G�ZY<;>f3t:c@d·f8;6"Ñ�3C0@d3}G�<v:=GF`g<w2�8?Ñ72"<;:=69GF8;3�`4:Ä`4<w2�GaHJ3¦z�6�3�`÷G)69<�Gf3�Hx3�`?`;2"8?:c�=Å�z.3C¤98w27z.3¦·a3}84DE678?@F2�GaHJ3�©�ô G¸`469@p3¦H}29`g3�`JZ)2"¤73}0`43CGa`4:c<?:=Ñ�:=<gÅ 29HJ<;ea2"�c�=Å�:=@d·f8;6�Ñ�3�`�@d3�2�G´8;3�`4·a67Ga`43¦<?:c@d3�`�¶�Å�@F2":cG.<Ù2":=G):=Gf¤Ú<;>f3Ú678wz.3}8;:=Gf¤Ê6�D�`43�¾�ef3}G�<?:Ä2"�8?3µ¾¨ef3µ`4<w`b:Ä`?`gef3�zd:=GF�=67¤9:ÄH}2"�c�=Åp29`?Hx3}Gaz.:cGf¤Ê698Ùz.3}8}©�f698Ê3}â�·a3}8?:c@d3}G�<w`�ea`4:cGf¤�<?>f3�DEef�=�Ø`4Å)`4<?3C@ <;8w29Hx3�`JZv¥�§B`;HÁ>)3�z.ef�c:=Gf¤×¤9:=Ñ�3µ`¢·)8?3�HJ3µz.3}GaHJ3�<?6�<;:=@d3C0HJ8;:=<?:ÄH}2"�ä2"GazF<?:c@d3}0E�=:=@�:�<?3�zÊ8?3µ¾¨ef3µ`4<w`ÚÞE6�Ñ�3}8�<?:c@d3}0EGf69GaHx8?:=<;:'H}2��f8?3µ¾¨ef3µ`4<w`wßw©]¹b>f:'`�8?3µ`4ef�c<w`b:=GF3}G)>a2"GaHx3�z`4Å)`4<;3}@ó·a3}8gDE698?@¸2"GaHJ3ÖZv29`´@d3µ29`4e)8?3�z$¶�Ž<;>f3×2"·f·f�c:'H}2�<?:c69Gf0¡`4·a3�HJ:�ã&Hd@d3}<;8?:'HC`J©½¬�<Ê<?>)3_`;2"@d3F<;:=@d3�Z¥¨§Ð2"�c¤9678?:=<;>f@F`´·)8?6�z.eaHx3�@´eaHw>¿�'2�8?¤93C8d@d3�2�Gõ8?3µ¾¨ef3µ`4<�8?3�`g·Y67Ga`43ð<?:c@d3�`dÞE3�© ¤)©=Zv6"Ñ�3C8d2�Gæ678wz.3}8p6"D@F2�¤9Gf:c<?eaz.3¦¤78?3�2�<?3}8hDE678Fsvu\ÛhÀ&�Á-;ÂwÂwßw©�¹b>f:Ä`Úz.3}@p69Ga`g<?8w2�<?3�`b<;>f3Ê:=@p·Y678?<Ù2"GaHJ3¦6�Db:cGaHJ�ceaz.:=G)¤�29H}HJe)8w2"<;3>f6Ö`4<yDE3}3�z.¶I29HwÃÚ:=G�z.:Ä`4ê`?Hw>f3�z�ef�=:cGf¤h3Câ.·a3}8;:=@d3}G�<w`��}<?8Ù29z.:c<?:=67Ga2"�Iz.:'`gÃt`gef¶a`gÅf`g<?3}@ 2"Ga2��=Å)`4:'`]Þ�ea`g:=Gf¤Ú67Gf�=Å`4e)¶a`4Å)`4<;3}@Ì·a3}84DE678?@F2�GaHJ3�@d3}<?8;:'H}`wßb£]69ef�Äz$�'2�¶a3}�]¥¨§|`?Hw>f3�z.e)�=:=G)¤F29`ª2Ƕa27z½z.3�`g:=¤9GöHÁ>f67:'HJ3Ö©dñh6Ö`4<?0¶a27`43�zÊ¥�§Í`?Hw>f3�z.ef�c:=Gf¤�£]698;Ãf`�¶a3�`g<�:�Da<?>)3�z.:Ä`4Ã)`+:cGÆ<;>f3�`gef¶a`gÅf`g<?3}@ z.6ÚG)69<y>a2}Ñ�3]HJ67@d@F2"GIzÚ¾¨e)3}ef3}:cGf¤f©�yÑ�3}Gp2ÆÑ�3}8;Å�`4>f678?<1HJ67@d@F2"GIzʾ¨ef3Cef3h�c3}Gf¤7<?>×Þ�3�© ¤f©=Z�¥¦698 ¯ ß z.3}¤78w29z�3�`Ü6�Ñ�3}8Ù2"�=�&`gÅf`g<?3}@[·a3}8gDE698?@¸2"GaHJ3Þ�2��=¶a3}:c<�:=@d·f8;6�Ñ.:cGf¤¦@d3�2"Gp8?3�`g·Y67Ga`43ª<?:c@d3�`ÁßÙ©

Page 108: Aggressive Centralized and Distributed Scheduling ofDisk Requests

® ±

C-LOOKi 2Q C-LOOKl SPTF SPCTF! 2Q SPTFj 2Q SPCTF Scheduling Algorithmm

0

200

400

600

800

1000

Mea

n R

espo

nse

Tim

e (m

s)

n

Þ�2¨ßÚá_3�2�G#"�3�`g·Y67Ga`43 ¹b:=@d3

C-LOOKi 2Q C-LOOKl SPTF SPCTF! 2Q SPTFj 2Q SPCTF Scheduling Algorithmm

0

50

100

150

200

250

Appl

icat

ion

Run

Tim

e (s

ec)

o

ÞE¶qß]¬h·f·)�=:'HC2"<?:c69G$"�efG×¹b:=@p3�����a� �"!�#&% #&%�*Êsvu\ÛhÀ&�Á-;ÂwÂx/y�fef�=�c0� ÚGf6�£��c3�z.¤93¢¥¨§ª©{5v« ¬1�=¤9678?:c<?>f@|A�3}8gDE698?@¸2"GaHJ3

Page 109: Aggressive Centralized and Distributed Scheduling ofDisk Requests

®('

Scheduling Algorithm)0

20

40

60

80M

ean

Res

pons

e T

ime

(ms)

*CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

Þ�2¨ßÚá_3�2�G#"�3�`g·Y67Ga`43 ¹b:=@d3

Scheduling Algorithm)0

50

100

150

200

250

300

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

ÞE¶qß+á_3�2�G_¼169Gf0g5v69@d·)ef<?3ª¹b:=@p3

�����a� ��!W#&% #a#&*Æ�ÅØ9�¨ï%ÙÚ-x�.Z K0/ `43C8}/1¥¨§ ° Hw>f3�z.ef�c:=Gf¤p¬h�c¤9698;:=<;>f@áA�3}84DE678?@F2�GaHJ3ÚDE698211:43&3}8?3CG.<5v67@d@F2�Gazǧ1ef3}ef3ª\q3}G)¤9<?>I`

Page 110: Aggressive Centralized and Distributed Scheduling ofDisk Requests

®65

Scheduling Algorithm)0

20

40

60

80

100

120M

ean

Res

pons

e T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

Þ�2¨ßÚá_3�2�G#"�3�`g·Y67Ga`43 ¹b:=@d3

Scheduling Algorithm)0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

ÞE¶qß+á_3�2�G_¼169Gf0g5v69@d·)ef<?3ª¹b:=@p3

�����a� ��!W#&% #&7�*Æ�ÅØ9�¨ï%ÙÚ-x�.Za¥ / `43}8Ù`J/v¥¨§ ° Hw>f3�z.ef�c:=Gf¤ ¬h�=¤7698;:=<?>)@BA�3C84DE698;@F2"GIHJ3÷DE678811:43&3}8?3CG.<5v67@d@F2�Gazǧ1ef3}ef3ª\q3}G)¤9<?>I`

Page 111: Aggressive Centralized and Distributed Scheduling ofDisk Requests

®(9

Scheduling Algorithm)0

50

100

150

200M

ean

Res

pons

e T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

Þ�2¨ßÚá_3�2�G#"�3�`g·Y67Ga`43 ¹b:=@d3

Scheduling Algorithm)0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

ÞE¶qß+á_3�2�G_¼169Gf0g5v69@d·)ef<?3ª¹b:=@p3

�����a� ��!W#&% #;:&*Æ�ÅØ9�¨ï%ÙÚ-x�.Z ¯</ `43}8Ù`J/v¥¨§ ° Hw>f3�z.ef�c:=Gf¤ ¬h�=¤7698;:=<?>)@BA�3C84DE698;@F2"GIHJ3÷DE678811:43&3}8?3CG.<5v67@d@F2�Gazǧ1ef3}ef3ª\q3}G)¤9<?>I`

Page 112: Aggressive Centralized and Distributed Scheduling ofDisk Requests

®9®

Scheduling Algorithm)0

100

200

300

400

500M

ean

Res

pons

e T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

Þ�2¨ßÚá_3�2�G#"�3�`g·Y67Ga`43 ¹b:=@d3

Scheduling Algorithm)0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

ÞE¶qß+á_3�2�G_¼169Gf0g5v69@d·)ef<?3ª¹b:=@p3

�����a� ��!W#&% #&=�*Æ�ÅØ9�¨ï%ÙÚ-x�.Z 90/ `43}8Ù`J/v¥¨§ ° Hw>f3�z.ef�c:=Gf¤ ¬h�=¤7698;:=<?>)@BA�3C84DE698;@F2"GIHJ3÷DE678811:43&3}8?3CG.<5v67@d@F2�Gazǧ1ef3}ef3ª\q3}G)¤9<?>I`

Page 113: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K?>@>

Scheduling Algorithm)0

200

400

600

800

1000M

ean

Res

pons

e T

ime

(ms)

*CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

Þ�2¨ßÚá_3�2�G#"�3�`g·Y67Ga`43 ¹b:=@d3

Scheduling Algorithm)0

50

100

150

200

250

App

licat

ion

Run

Tim

e (s

ec)

A CQ = 1+CQ = 2+CQ = 4+CQ = 16+

Preseek, Full-

SPTF.CW.SSR. SPCTF.CW.SSR. C-LOOK.CW.SSR C-LOOK.CW.SSR

ÞE¶qß]¬h·f·)�=:'HC2"<?:c69G$"�efG×¹b:=@p3

�����a� ��!W#&% #&B�*dsvu\ÛhÀ&�w-?ÂwÂx/]¥¨§ ° HÁ>)3�z.ef�c:=Gf¤�¬h�c¤9678?:=<;>f@­A�3C84DE698;@F2"GIHJ3¦£�:=<?>C1h:D3q3C8?3}G�<Ú5v69@d0@¸2"Gaz_§1ef3}ef3¢\q3}Gf¤9<;>a`

Page 114: Aggressive Centralized and Distributed Scheduling ofDisk Requests

E2F GIHKJ�LNM O

E2PRQ<SUTWVYX[Z]\�PR^ _#`bacPR^�d�X[Z[Qce VRSfS�acP g Z[hji

k_6�z.3}8;GFz.:'`gÃÊz.8;:=Ñ�3�`�HJ69G�<w2�:=G�·Y6�£]3}84DEef�a3}@�¶a3�zfz.3µzÆ@d:ÄHJ8?67·f8?6�HJ3µ`?`4678w`y<?6¦>a2�Gaz.�c3h·a3}8;:=·f>f3C8w2"�a¶feI`:=G�<?3C84D¡29Hx3�`JZf:cG.<;3}8?·f8;3}<12"GIz�`43}8;Ñ.:ÄHJ3¦:=GaHJ67@d:=G)¤Ê8?3�¾�ef3�`g<w`JZ&2"GIz_@F2"Ga2�¤93 `43}¤7@d3}G�<?3�zFzf2�<w2dH}27HÁ>)3�`J©1ô�G29z)z.:=<;:=69GäZbz.:Ä`4ÿz�8?:=Ñ�3¸HJ69G�<?8;69�=�c3}8w`ÊHC2"G¿@F2":cG.<Ù2":cG¿2"Gaz¿8?3}678wz.3C8Ê69Gf0E¶a6�2"8Ùz˾¨e)3}ef3�`t6�DÚ·a3}Gaz�:=Gf¤ð8?3}0¾�ef3�`4<Ù`J©�¬ z.:'`gÃ.0E¶a27`43�z×HJ3}G�<?8w2��=:cî}3�zd`;HÁ>f3µz.ef�=3C8b>a27`h<?>f3ª27z.Ñ72"G�<w2"¤73Ê6"D]3�27`4Å×2"GazF:=@d@p3�z.:c2"<;3Ú27H}HJ3�`;`<?6�<;>f3pHJ69@d·)�=3}<;3�`43}<ª6"D¢z.:'`gýHJ67G.ãa¤7ef8w2�<?:=67GÍ2"Gaz¿`4<Ù2"<;3d:=G.DE678?@F2�<?:c69G�©�Ó1Gf0�¶a6Ö2"8wz½ãa8?@�£�2�8?3FÞ¡2"Gaz>a2�8wz.£Ø2"8?37ßÚHC2"G�¶a3´<;efGf3�z_<;6F3}â.·)�=69:c<h<;>f3Ê@F2�â.:c@´ef@|2"@p69efG�<Ú6"DØHJ67GaHJef8;8?3}GIHJÅ_¶a3}<g£b3C3}G_8;3�¾¨e)3�`4<Ù`:=GÈ`43}8;Ñ.:ÄHJ3ª2"<¦2pz.:'`gÃq©¦ÓhG×<?>f3ª69<;>f3}8Ú>a2�GazqZ�`gÅf`g<?3}@p0��c3}Ñ�3}�&`?Hw>f3�z.e)�=:=G)¤´:cG.DE698;@F2"<;:=69GF@�ea`4<�¶a3�HJ67@d0@�efGf:'HC2"<?3µzpDE8;69@Ì<;>f3Ê>f6�`g<�Þ�3�© ¤f©=Zaea`g:=Gf¤×29z)z.:=<;:=69GI2"�yãa3}�Äzf`h:=G�<;>f3Ê8?3µ¾¨ef3µ`4<¦HJ67G.<;8?67�y¶f�=6�HwÃ)`Áßw©lk_698;3:=@p·Y678?<Ù2"G�<?�=ÅÖZY<;>f3Ê69Gf0E¶a6�2�8wz½¾�ef3}ef3ª6"DØ·Y3CGaz.:=G)¤Ç8;3�¾�ef3�`4<Ù`h:'`1�=:=@p:=<?3µz´¶.Å×<?>f3�2�@d69e)G.<16"D÷2µÑ72�:=�'2�¶f�=3z.:Ä`4Ã�0��c3}Ñ�3}��@d3}@p698?ÅèÞ�3}â)HJ�=eIz.:=Gf¤ð<?>)3½zf2�<w2¿H}27HÁ>f3ð2�Gazõãa8?@�£�2�8?3�`g<?678w2"¤739ßw©ÿ¹b>f3��c:=@d:c<?3�z¿¾�ef3}ef3�=3CGf¤9<;>�:=@d·a2�:=8Ù`÷<;>f3Ê·a3}84DE678?@F2�GaHJ3Ê6"D÷2dz.:Ä`4Ã�0�¶a27`43�zð`?Hw>f3�z�ef�=3}8]�q69GIHJ3´<;>f3Ê69G)0�¶a6�2�8wz½¾�ef3}e)3Ê:'`÷DEef�c��Z29z)z.:=<;:=69GI2"�b8;3�¾�ef3�`4<Ù`Æ@�ea`4<¦¶a3d¶fe�3q3C8?3�z½¶�Å�<?>f3d>)6�`4<�2�Gaz¿2"8;3Ç<;>f3}8;3JDE698;3´Gf67<�HJ69GI`4:'z�3}8?3�zð¶.Å�<;>f3z.:Ä`4Ã�0�¶a27`43�z�`;HÁ>)3�z.ef�c3}8}©¦ô�GaHJ8;3�29`g:=Gf¤�<?>)3Ê@F2"â�:=@�ef@|¾¨ef3Cef3t�c3}Gf¤9<;>ð2"�c�=3}Ñ�:'2�<?3�`�<?>f:Ä`÷·)8?69¶)�=3}@Ð2"<Ú<;>f3HJ6Ö`4<16"D 29zfz.:c<?:c69Ga2���·Y3C8?0¡z.:'`gÃÇ@p3}@d698;ÅdÞ¡2"GazF·Y6Ö`?`g:=¶f�cÅFHJ69@p·fef<w2�<?:c69Gqßv8;3�`467ef8wHJ3µ`J©¹b>f:'`ÊHw>a2�·f<?3}8Ê3Câf2�@d:=Gf3µ`Æ2�Ñ72"8;:=3}<gÅð6"D¢z.:'`gÃ.0E¶a29`g3�zõHx3}G.<;8w2��=:=îC3�z$`;HÁ>)3�z.ef�c:=Gf¤È2"�=¤7698;:=<?>)@F`J©Î¹b>f33}â�·a3}8?:c@d3}G�<w`v2"8;3Æ·I2"8?<;:=<;:=69G)3�zd¶a29`g3�zÇ67GÇ<;>f3¦<gÅ.·a3¦6"Dv:cG.DE698;@F2"<;:=67Gdea`43µz¸¶�Åd<;>f3ª`?Hw>f3�z.ef�c3}8}©O$m?n _#`bacPR^�d�X[Z[Qce opZ�S�a qrQcs�t0Tu VvS�Z]twQ x#TWtwu yz{PRX]tvop|

}1ù�~bù�~ �8�����f���j�hý��r�����<���W���r�¹b>f:'`¦`g3�HJ<?:c69Gðea`43µ`Æ<?>)3�`4:=âðñ»Aº2"Gaz�1��b5º<?8Ù29HJ3µ`¢<;6�`g<?eaz.Å�<;>f3�3�3&3�HJ<w`Ú6�D1`43µ¾¨ef3CG.<;:'2"� `4<?8;3�2"@69·)<?:=@p:=î�2�<?:=67Ga`¦2"Gazð@F2"â�:=@�ef@áHJ69@p@F2"Gaz�¾�ef3}e)3´�c3}Gf¤9<;>a`Æ67G¿z.:Ä`4Ã�0�¶a27`43�z¿`;HÁ>f3µz.ef�=3C8w`Úea`4:cGf¤_67Gf�=Å>a2�8wz.£Ø2"8?3C0�`g·Y3µHJ:{ã&HtÃ�Gf6�£��=3µz.¤93�©»ô�<ÚHJ67GaHJ�ceaz.3�`�£�:=<;>ð2dHJ69@p·a2"8;:'`467G_6�D�z�:'`4Ã�0E¶a29`g3�z�2"Gaz�>f6Ö`4<?0E¶a27`43�zHJ3}G�<?8Ù2"�c:=î}3�z�`?Hw>f3�z�ef�=:cGf¤f©

�ä!���� !��;�������������!���� �<�������Ý�����������;��ê¬Ú`v2"�c�f3}â�·Y3C8?:=@p3}G.<Ù`q:=G�<?>f:Ä`yHw>a2"·f<;3}8yea`g3Úz�:'`4Ã)`y£�:=<;>Ê·f8?3�`g3}3}Ã�:=Gf¤¢H}2"·a2�¶f:=�c:=<gÅ�Z9<;>f3}8;3�:'`�Gf6 29z.Ñ72�Gf0<w2�¤93¦<?6�Hx69GaH}2�<?3}GI2"<?:cGf¤t8;3�¾�ef3�`4<Ù`b27`b<?>f3}Åp2"8;8?:cÑ�3Ú2�<12Êz.:'`gÃq©v¹b>f3¢`43�¾�ef3}G�<?:Ä2"�&`?Hw>f3�z.e)�=:=G)¤Æ67·f<?:c@d:=îµ2"0<?:c69G�Z 69G¿<?>)3´67<?>f3}8ª>a2"GIzqZvH}2"GÎ:=@d·f8;6�Ñ�3Ê69Gf0E¶a6�2"8Ùz¿H}29Hw>f3�>f:=<ª8w2"<;3�`t2�Gaz½8?3�z�eaHJ3�@d3�2"G�8;3�`4·a67Ga`43<?:c@d3�`x©���:=¤7ef8?3µ` ' © K ì ' © ' `4>f6�£½<;>f3b3�3q3µHJ<w`�6"Da<;>f:'`�69·)<?:=@p:=î�2�<?:=67GÚ69G z.:'`gÃ.0E¶a27`43�zÊHJ3CG.<;8w2"�c:=î}3µzÚ`?Hw>f3�z.e)�=0

K?>�K

Page 115: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K?> ¥

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

50

100

150

200

Mea

n R

espo

nse

Tim

e (m

s)

� No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

Þ���ß� U¡£¢¥¤¦¢?¢}Ã$§W¨9@p@$�ª©azF§¬«&¢?«�¢?­®©f¤

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

50

100

150

200

Mea

n R

espo

nse

Tim

e (m

s)

� No Opt.SSR.SSW.SSR

ÞE¶qß]��«f�=�U§W¨7@d@$�ª©Iz¸§�«�¢?«&¢?­¯©f¤°�±�²Y�j³[´#7�µ�¶¸·º¹»½¼¯¼D¾(¿jÀ9© 5 ±[Á0 ° ¢�¾�«�¢?©�ã­Ä�"� °6ÅÇÆ ¢µz�«f�¯­®©f¤Ê¬1�=¤(¨@¡£­®Ã Æ @f j¢?¡¦È�¨@¡?@$�[© Å ¢

Page 116: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À > ²

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Þ���ß� U¡£¢¥¤¦¢?¢}Ã$§W¨9@p@$�ª©azF§¬«&¢?«�¢?­®©f¤

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

5

10

15

20

25

30

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

ÞE¶qß]��«f�=�U§W¨7@d@$�ª©Iz¸§�«�¢?«&¢?­¯©f¤°�±É²a�j³[´#7�µËÊÌ·��&��ͪÎ�»Ï¿UÀ9©³¥9±ªÁºÂ ° ¢�¾�«�¢?©�ã­Ð��� °�Å½Æ ¢�z�«f�¯­®©f¤Ê¬h�c¤(¨@¡£­¯Ã Æ @Ñ r¢?¡¦È�¨@¡?@$�[© Å ¢

Page 117: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À >�¯

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

50

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

Þ���ß� U¡£¢¥¤¦¢?¢}Ã$§W¨9@p@$�ª©azF§¬«&¢?«�¢?­®©f¤

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

50

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

ÞE¶qß]��«f�=�U§W¨7@d@$�ª©Iz¸§�«�¢?«&¢?­¯©f¤°�±�²a�r³[´c7Òµc��·¬ÓÕÔ'�½Ö�ïhÂ]×�¿a¥.©Õ±[Á0 ° ¢�¾6«&¢?©�Ã�­Ð��� °�Å½Æ ¢�z�«)�¯­¯©)¤Ê¬h�c¤(¨(¡�­¯Ã Æ @f r¢?¡�È�¨(¡;@$�ª© Å ¢

Page 118: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À > ±

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

Sat

urat

edS

atur

ated

Sat

urat

ed�

Þ���ß� U¡£¢¥¤¦¢?¢}Ã$§W¨9@p@$�ª©azF§¬«&¢?«�¢?­®©f¤

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

Sat

urat

ed

ÞE¶qß]��«f�=�U§W¨7@d@$�ª©Iz¸§�«�¢?«&¢?­¯©f¤°�±�²Y�j³[´#7�µ®%Ò·1�ÌØ?Ô¯Ö?Ùq�;¿&¥.©³±ªÁ0 ° ¢�¾6«&¢?©�Ã�­Ð��� °6ÅÇÆ ¢µz�«f�¯­®©f¤�¬h�c¤(¨(¡�­¯Ã Æ @{ j¢?¡¦È�¨@¡?@$�[© Å ¢

Page 119: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À >@'

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

Sat

urat

edS

atur

ated

Sat

urat

ed�

Þ���ß� U¡£¢¥¤¦¢?¢}Ã$§W¨9@p@$�ª©azF§¬«&¢?«�¢?­®©f¤

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

ÞE¶qß]��«f�=�U§W¨7@d@$�ª©Iz¸§�«�¢?«&¢?­¯©f¤°�±�²Y�j³[´#7�µÐÚ�·ºÛ��£Ü�»x�½¿�À7© > Á0 ° ¢�¾�«�¢?©�ã­Ä�"� °6ÅÇÆ ¢µz�«f�¯­®©f¤Ê¬1�=¤(¨@¡£­®Ã Æ @Ñ r¢?¡�È�¨(¡?@Ý�ª© Å ¢

Page 120: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À >�5

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

ed�

Sat

urat

ed

Sat

urat

ed�

Sat

urat

edS

atur

ated

Sat

urat

ed�

Sat

urat

edS

atur

ated�

Sat

urat

edS

atur

ated

Sat

urat

ed�

Þ���ß� U¡£¢¥¤¦¢?¢}Ã$§W¨9@p@$�ª©azF§¬«&¢?«�¢?­®©f¤

C-LOOK� LOOK� SSTF� VSCAN(0.2) SPTF ASPTF(6) SPCTF� ASPCTF(6)�Scheduling Algorithm�

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Sat

urat

ed�

Sat

urat

edS

atur

ated

Sat

urat

edS

atur

ated

Sat

urat

ed�

ÞE¶qß]��«f�=�U§W¨7@d@$�ª©Iz¸§�«�¢?«&¢?­¯©f¤°�±�²a�r³[´#7�µ®7�·hï�»�À&¾��½ÞÉ¿ÌÀ9© > Á0 ° ¢�¾�«�¢?©�ã­Ð��� °�Å½Æ ¢�z�«f�¯­®©f¤Ê¬h�c¤(¨@¡£­¯Ã Æ @f r¢]¡¦È�¨(¡;@$�ª© Å ¢

Page 121: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À >@9

­¯©)¤f©Ê¹ Æ ¢Ê@Ý�"â�­=@<«f@ Å ¨9@d@$�[©az_¾�«�¢?«&¢t�¯¢]©f¤(Ã Æ £ß�(¤v¤¦¢?ÃÕã¨àÀ}¥ 9 Þá�dÑ(���¯«�¢ÚÛ�«â¤¦Ã£­�ã;¢�z_¶;¢}�®¨"£Úß�È�¨@¡ã���=�z�­Ä¤4Ã&¤J©�¹ Æ ¢ z��ªÃÏ�à·;¨@­¯©�ý¤��ª¡£¢vÈ�¡£¨7@äÃ Æ ¢$�?Ã�©�¢?¢[�0¨ªÈå¢[� Å½Æ Ã�¡½� Å ¢�Ôæ¤�¤�¢?ì¨[ÈW¡£¢¥¤4·;¨(©;¤�¢ãÃ�­=@ç¢ Å «�¡?Ñ�¢[¤x©b��¨@¡�&��ͪÎ軽¿U¤�¢�¾6«&¢?©�Ã�­Ð���W¤ Å½Æ ¢�z�«)�¯­¯©)¤w¨[È�¡£¢¥�9z�¡£¢�¾�«�¢[¤�ý¤Úz�¢ Å ¡£¢[�@¤¦¢[¤Ú@碥�ª©#¡�¢[¤4·;¨@©;¤¦¢çÃ�­=@碥¤b¶.Å�«f·�Ã�¨ ®¨Ò ©��¨(¡�Ã Æ ¢l¨(Ã Æ ¢?¡�ãaÑ�¢v㡽� Å ¢[¤�¿�Ã Æ ­Ä¤�¨7·�ã­c@ç­=î[�[ã­®¨(©$�?3�¢ Šý¤�@ç¢[�[©é¡�¢[¤4·;¨@©;¤¦¢0Ã�­=@ç¢[¤v¶.Ÿ¥ Ò ¨(¡1�¯¢[¤�¤÷£ Æ ¢?©«;¤�­¯©f¤ç§Wêáë�Ó¦ÓÚ ì¨(¡�Ã Æ ¢ °  v¹��rêE¶;�(¤�¢�z$�"�c¤(¨(¡�­¯Ã Æ @$¤J©v¹ Æ ­Ð¤Ü@Ý�ªÃ Å½Æ ¢[¤UÃ Æ ¢Ú¤(¢]©�¢?¡½���q¶;¢ Æ �}Ñ�­¯¨@¡¨9¶â¤¦¢?¡;Ñ�¢�zÈ�¨(¡ Æ ¨è¤¦Ã£êE¶;�@¤¦¢�zc¤ Å½Æ ¢�z�«f�®¢?¡½¤v£�­¯Ã Æ ¤¦¢µ¾6«�¢]©�Ã�­Ð�"�̤ ÅÇÆ ¢µz�«f�¯­®©f¤0¨ªÈí¡£¢¥�9z�¤¦Þ�¤�¢?¢l¤¦¢ Å Ã�­¯¨@©_±�©¯À7©Õ¥¨ßÙ©° ¢�¾�«�¢?©�ã­Ä�"��¤ ÅÇÆ ¢�z�«f�®­¯©f¤0¨[Èy£�¡�­¯Ã£¢¥¤ Æ �(¤��t@î­¯©�­c@$�"��¢�3�¢ Å ÃÈ�¨(¡î¹»½¼¯¼ï¾(¿��&��ͪÎ�»Ï¿Û���Ü�»x�½¿��ª©IzWï�»¡À�¾��½Þ£ Æ ¢?©�«;¤¦­®©f¤ð§Wêáë�Ó¦ÓÚ f¨(¡0Ã Æ ¢ °  Ü¹��jê�¶;�@¤¦¢�zñ���=¤(¨@¡£­®Ã Æ @$¤x©_��¨@¡wÓÕÔ'�½Ö�ïhÂ]×l�ª©azÝ�¸Ø?Ô¯Ö?Ùq��¿í¤¦¢�¾�«�¢?©�ã­Ä�"�¤ Å½Æ ¢�z�«f�¯­®©f¤�¨ªÈª£�¡£­®Ã£¢$¡£¢µ¾6«�¢¥¤¦Ã½¤<� Šã«;���=�=ÅÍz�¢C¤(¡½�7z�¢[¤´·;¢?¡�È�¨(¡;@$�ª© Å ¢Ç¶�Åñ��·f·�¡£¨�â�­=@$�[ã¢}�cÅ¿¥ Ò È�¨@¡wÃ Æ ¢ U¡£¢[¤�¢?¢}Ã�­¯©f¤ Å ¨9@p@$�ª©azp¾6«�¢]«�¢?­¯©)¤ Å ¨@©.ãa¤(«&¡½�ªÃ�­¯¨@©�©æò¹ Æ ¢�¤�¢�¾�«�¢?©�ã­Ð����¤ Å½Æ ¢�z�«)�¯­¯©)¤¬¨7·�ã­c@ç­=î[�[ã­®¨(©v¤�ã¡£¨@©f¤9�cÅ0�?3�¢ Šý¤�Ã Æ ¢]·;¢?¡¦È�¨@¡?@$�[© Å ¢¨[ÈÌë�Ó¦Ó» Y¿ °f° ¹��b¿�ª©Izðó ° §]¬Ú¼ªÞ > ©³¥¨ßÙ© ° ¢ Å Ã�­¯¨(©Î±.©®À9©³¥_z�­Ä¤ Å «;¤�¤¦¢[¤ Æ ¨�£ôÃ Æ ¢[¤¦¢î�"�c¤(¨@¡£­¯Ã Æ @$¤ Æ �[©az.�¯¢Ý¤¦¢�¾�«�¢?©�ã­Ä�"�W¤�ã¡£¢¥�"@$¤¨ªÈl¡�¢�¾6«&¢[¤¦ÃϤà£�­®Ã Æ �[©azõ£�­¯Ã Æ ¨(«&ÃçÃ Æ ¢õ¤¦¢�¾�«�¢?©�ã­Ä�"��¤ ÅÇÆ ¢µz�«f�¯­®©f¤�¨9·&ã­=@î­=î[�[ã­¯¨@©ÏÞ�¤¦¢]¢_·;��¤(¢ ' ¥�ßw©í¹ Æ ¢¤¦«)¶�êɨ7·�ã­c@$�"�夦¢�¾�«�¢?©�ã­Ä�"�W¤ ÅÇÆ ¢µz�«f�¯­®©f¤�¶¸¢ Æ �}Ñ�­®¨(¡v¨ªÈ�ë�ÓÆÓ» {�[©azðó ° §]¬Ú¼tÞ > ©Õ¥�ß�­Ð¤¦¾�«�­¯Ã�¢ã¨9¶�Ñ�­¯¨(«â¤ö­®©ãa¤@«�¡£¢ ' ©¯Àî�ª©az$ãa¤@«�¡£¢[¤ ' ©³²µì ' © ' ©$ô�©ñ¤�¢}Ñ�¢?¡Ï�"� Å �@¤¦¢[¤�¿UÃ Æ ¢î«;¤¦¢ç¨[È�Ã Æ ¢¥¤¦¢$���=¤(¨@¡£­®Ã Æ @$¤�¡�¢[¤¦«f�®Ã½¤v­¯©�¤£�ªÃ�ê«�¡Ï�ªÃ£­®¨(©÷¨ªÈlÃ Æ ¢ðz�­Ð¤gÃø¤�«f¶;¤gÅ�¤�ã¢}@ �ªÃ$Ã Æ ¢õ¤¦¢}�®¢ Å Ã�¢�zùÃ�¡½� Å ¢à¤ Å ���¯­¯©)¤ðÈá� Å Ã�¨(¡Ï¤J© �r­=¤@«�¡£¢[¤ ' © ¯ �ª©az ' ©³±¤ Æ ¨"£ Æ ¨�£ô¤�¢�¾6«&¢?©�Ã�­Ð���U¤ ÅÇÆ ¢µz�«f�¯­®©f¤î�"�=�®¨�£�¤ °f° ¹���ã¨c�ªÃ�ý�[­¯©�·;¢?¡¦È�¨@¡?@$�[© Å ¢ª@w« ŽÆcÅ �¯¨è¤¦¢?¡Õã¨$Ã Æ �[Ãv¨ªÈ§Wêáë�ÓÆÓ» úÈ�¨(¡¦�ÌØ?Ô¯Ö?Ùq�c�[©azøÛØ�£Ü�»x�w©b��¨@¡Æ�&�&ͪÎ�» Å ¨(©�ãa¤(«�¡Ï�ªÃ�­¯¨(©â¤h£�­¯Ã Æ  U¡£¢[¤�¢?¢}à Š¨9@d@$�[©azd¾�«�¢?«�¢]­¯©f¤Þ�¤�¢?¢ÆãI¤(«�¡�¢ ' ©³¥(��ß��ª©azðÓÕÔ'�½Ö�ï1Â]× Å ¨@©.ãa¤@«�¡½�[ã­¯¨@©;¤Ú£�­¯Ã Æ ��«f�=� Å ¨9@d@$�[©azd¾�«�¢?«�¢]­¯©f¤×Þ�¤�¢?¢Æãa¤@«�¡£¢ ' ©³²"¶qßÏ¿Ã Æ ¢�¤¦¢µ¾6«�¢]©�Ã�­Ð�"��¤ ÅÇÆ ¢�z�«f�®­¯©f¤à¨9·�Ã�­=@ç­cî[�ªÃ�­¯¨@©;¤ã¢?©;��¶f�¯¢ °f° ¹��úÃ�¨½@$�[¡?¤(­®©;�"�c�=Åà¨(«�Ã;·;¢?¡¦È�¨@¡?@ §Wêáë�Ó¦Ó» Þ�£�­®Ã Æ ÀÁ쨥 Ò �¯¨�£b¢?¡b@碥�ª©$¡£¢[¤g·;¨(©;¤�¢ãã­c@ç¢[¤wßw©ål�;�ñ�r��³[±Eê?�;�ø��û»éé±Eê}ë�üÏý0�fê?´�þÿ�����r´�þ �r��±É�j²��ç��²;�;³ª±Ð���j�¿ê

¬�¤y£��@¤�ã¡�«�¢�È�¨(¡ Æ ¨�¤�ãêE¶;�(¤�¢�z$¤ Å½Æ ¢�z�«)�¯­¯©)¤�¿�§Wêáë�Ó¦ÓÚ º¤@¢?©�¢?¡Ï�"�=�cÅt·�¡�¨�Ñ�­Äz�¢[¤UÃ Æ ¢1¶;¢[¤¦Ãv·;¢?¡�È�¨(¡?@Ý�ª© Å ¢�"@î¨(©f¤cÃ Æ ¢î¤¦¢?¢CÃ�ê�¡£¢�z�« Å ­¯©)¤#���=¤@¨(¡£­®Ã Æ @ݤJ©d��¨@¡�¹»½¼®¼D¾(¿ °f° ¹��æ·&¡£¨�z�« Å ¢[¤ã«f·à㨠¯�Ò �®¨�£¢?¡¦@ç¢[�[©�¡£¢?ê¤4·;¨@©;¤¦¢�Ã�­=@碥¤J©�¬ùÈ�¢}£ Å ¨@©.ãa¤@«�¡½�[ã­¯¨@©;¤�«â¤¦­¯©)¤à�Y��ͪÎ�»W�[©azÝÓÕÔ'�½Ö�ï1Â]×U�"�Ĥ¦¨l� Å½Æ ­¯¢CÑ�¢b¶;¢?ãÃ�¢?¡y·;¢?¡�È�¨(¡?@Ý�ª© Å ¢£�­¯Ã Æ�°f° ¹��æÞá�(¤©�¨@ã¢�zc�"¶;¨�Ñ�¢9ßw©¬ Å ¡�¨�¤£¤í�"�=�&¤¦­câãÃ�¡½� Å ¢[¤�¿(Ã Æ ¢ °  Ü¹��jê�¶;�@¤¦¢�z<�"�c¤(¨@¡£­¯Ã Æ @$¤�·�¡£¨�Ñ�­'z�¢bÃ Æ ¢��®¨�£¢[¤�Ã�@碥�ª©ã¡�¢[¤4·;¨@©;¤¦¢�Ã�­=@ç¢[¤x©ô�©�Ã Æ ¢ Å �(¤¦¢0¨[ÈÚïÕ»�À&¾��ÇÞ�¿��Fz�­Ä¤4Ãõ¤¦«f¶;¤gÅ�¤�ã¢}@ «;¤¦­®©f¤c U¡£¢[¤�¢?¢}à Š¨9@p@$�ª©az×¾6«&¢?«�¢?­®©f¤ç¤��ªÃ�«�¡½�[ã¢[¤l�ªÃ�Ã Æ ¢¤¦¢C�¯¢ Å Ã�¢�zéÃ�¡½� Å ¢<¤ Å ���¯­®©f¤wÈá� Šã¨(¡�È�¨(¡v���=�U¨[ÈÃ Æ ¢<ë���¼¬êE¶;�(¤�¢�zà�"�=¤@¨(¡�­¯Ã Æ @$¤J©¦¹ Æ ¢ãÈ�«)�=�¯êEÃ�©�¨�£��¯¢�z.¤@¢0���=¤(¨@ê¡£­®Ã Æ @ݤ�¿�¨(©cÃ Æ ¢v¨(Ã Æ ¢?¡ Æ �[©az�¿Ì� Å½Æ ­¯¢CÑ�¢h@碥�ª©ç¡�¢[¤4·;¨(©â¤¦¢ãÃ�­=@碥¤�¨ªÈ ¥ 5 ì�² > @$¤w©��¨(¡�Ã Æ ¢öÈ�¨@«�¡�1��§�Ã�¡½� Å ¢[¤�¿ Å � Å½Æ ¢?êᤦ¢?©â¤¦­¯Ã�­=Ñ�­¯ÃgÅ�z�¢}¤@¡½�7z�¢[¤Ã Æ ¢Æ·;¢?¡�È�¨(¡;@$�ª© Å ¢�¨ªÈíÃ Æ ¢ °  v¹��rêE¶;�@¤¦¢�z�"�c¤(¨@¡£­¯Ã Æ @$¤t¶�Åñ«f·øÃ�¨øÀ@À Ò ©æ¹ Æ ­Ð¤Ê¶¸¢ Æ �}Ñ�­®¨(¡�@$�ªÃ ÅÇÆ ¢¥¤RÃ Æ �ªÃç¨[È °  v¹��rêE¶;�(¤�¢�z�¤ Å½Æ ¢�z�«)�¯­¯©)¤�¨ªÈvÃ Æ ¢¹W¾�hÀ&�Ç»;Âw¬È�«f�c�¤gÅ�¤�ã¢}@�Ã�¡½� Å ¢�Þ�¤�¢?¢�·;�"¤@¢ 5 ²#­¯©�¤¦¢ Šã­¯¨@©¿±.©®À9©³²¨ßw©×¬�¤¦£��(¤vã¡�«�¢wÈ�¨(¡õ¹W¾�hÀ&�Ç»?ÂwÂ�¿�Ã Æ ¢Å � ÅÇÆ ¢]ê�¤�¢?©;¤¦­®Ã£­cÑ�¢W�"�c¤(¨(¡�­¯Ã Æ @$¤q·�¡�¨�z�« Å ¢ Æ ­=¤ Æ ¢?¡ @ç¢[�ª©v¡�¢[¤4·;¨(©â¤¦¢Ã�­=@碥¤âÈ�¨(¡jÃ Æ ¢�1��§àã¡Ï� Å ¢[¤�¶;¢ Å �[«;¤¦¢b¨ªÈ�ª«&ã¨9@Ý�ªÃ£¢µz¢·&¡£¢�È�¢?à ÅÇÆ ­¯©f¤b¨(©RÈ�«)�=��¡£¢¥�9z Æ ­¯Ã½¤x©�« Æ ¢?©t·&¡£¢�È�¢?à ÅÇÆ ­¯©f¤b­Ð¤�¢?©;�"¶)�¯¢�z�¨(©)�=Å�¨@©t·;�[¡£Ã£­Ä�"��¡�¢[�9z Æ ­¯ÃϤ�ª©Izã¡£¢[�7zÆ@ç­Ä¤£¤¦¢¥¤�¿ °  §]¹��#�[©azʬ °  §]¹��bÞ ' ß̨(«�Ã;·;¢?¡¦È�¨@¡?@ °  Ü¹��c�ª©azª¬ °  v¹��bÞ ' ß½¿@¡£¢[¤g·¸¢ Šã­cÑ�¢}�=Å�©&ô�©Èá� Å Ã?¿����=�;���=¤(¨@¡£­®Ã Æ @$¤j¢}â.·;¢?¡�­¯¢?© Å ¢b�Æz�¢ Å ¡£¢¥�(¤¦¢�­®©t@碥�ª©0¡£¢¥¤4·;¨(©;¤�¢¬Ã�­=@碥¤��¥È�ã¢]¡UÃ Æ ­Ä¤ Å½Æ �ª©f¤@¢tÞ�«;¤¦­®©f¤�Ã Æ ¢1��§8Ã�¡½� Å ¢[¤ÁßÏ¿j�"�¯Ã Æ ¨(«)¤ Æ Ã Æ ¢<ë���¼¬êE¶;�(¤�¢�zð���=¤@¨(¡£­®Ã Æ @ݤh@$�ª­®©�ÃÏ�ª­®©#Ã Æ ¢ç¤��"@ç¢l¡£¢}�Ä�ªÃ£­cÑ�¢t·;¢?¡�È�¨(¡?@Ý�ª© Å ¢¨(¡Ùz�¢?¡�­¯©f¤)©¹ Æ ¢�È�«f�=�®ê�Ã�©�¨�£��¯¢µz.¤(¢v���=¤@¨(¡£­®Ã Æ @ݤ�ª¡�¢l�"�Ф�¨ç¤�¢?©;¤�­¯Ã£­cÑ�¢¬Ã�¨<�ª©�Åd·�¡�¢�È�¢?¡£¢]© Å ¢Ú¤@­=Ñ�¢?©çÃ�¨ãÈ�«f�=�Ì¡£¢[�7z Æ ­¯ÃϤÞɨ�Ñ�¢?¡�·â�ª¡£Ã�­Ð���U¡£¢[�7z Æ ­®Ã½¤wßw©R§b� ÅÇÆ ¢?ê�¤�¢?©;¤�­¯Ã£­cÑ�¢ °  v¹����"�=¤@¨(¡�­¯Ã Æ @$¤�¾6«&¢?¡?Å$Ã Æ ¢ã¨(©&ê�¶;¨��[¡wz Å � Å½Æ ¢¦@ç¨�z�¢}�

��� �������������������� �!#"�$&%'����()��+*,(� �-/.� ����0�&%'$�(1�0)� �2�.�$3����45�+6�*�7����0 �(8�0�9%�2���(�:5*�����)��/.��8*�70�3�0 "�70 �;�.�< �7�����4=��%+�>2� �4�7?%�2� "@ �7A6B�/7�CD%+�E�? >FG(� � H"@%+4� H����I��

Page 122: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À >7®

㨠z�¢?Ã�¢?¡?@ç­®©�¢�­4ÈÒ�t·;¢?©az�­®©f¤ã¡�¢�¾6«&¢[¤¦Ã]£�­=�=� Æ ­®Ã­®©wÃ Æ ¢ Å � ÅÇÆ ¢Ö©y��¨(¡ Æ ¨�¤�ãêE¶;�(¤�¢�z#¤ ÅÇÆ ¢µz�«f�¯­®©f¤�¿�Ã Æ ¢ Å � ÅÇÆ ¢¤¦­c@d·f�cÅ�­¯©az�­ Å �ªÃ�¢[¤ã¢?­®Ã Æ ¢?¡c� Æ ­®Ã½��¨(¡à�?@ç­Ä¤£¤��.©¿��¨(¡�z�­Ä¤4Ã�ê�¶â�(¤¦¢µzø¤ Å½Æ ¢�z�«f�¯­®©f¤�¿WÃ Æ ¢ Å � ÅÇÆ ¢d@ç¨�z�¢}�ß�"�Ĥ¦¨­¯©Iz�­ Å �[ã¢[¤j­4Èj��¡�¢[�9z Æ ­¯ÃW­Ä¤ö� Å ¨9@p·f�¯¢?Ã�¢[��¨(¡v�?·;�[¡£Ã�­Ð�"�Ä�ƶ;�@¤¦¢�z0¨(©p£ Æ ¢?Ã Æ ¢?¡W¨(¡W©�¨(Ãb���=�;¨ªÈ Ã Æ ¢�¡£¢�¾�«�¢[¤�ã¢�z¤¦¢ Šã¨@¡½¤0�ª¡�¢F·�¡£¢[¤�¢?©�Ãã­¯©ñÃ Æ ¢ Å � Å½Æ ¢�©ð¹ Æ ¢×z�¢�Èá�[«f�¯Ã<¤ ÅÇÆ ¢�z�«f�®¢?¡ Å ¨(©.ãI¤(«�¡Ï�ªÃ£­®¨(©Í¤(­=Ñ�¢¥¤Æ·�¡�¢ Å ¢�z�¢]© Å ¢çÃ�¨È�«f�c� Æ ­¯Ã½¤�¨�Ñ�¢?¡¦·;�[¡£Ã£­Ä�"� Æ ­®Ã½¤J© / ©�È�¨(¡�ã«�©;�[ã¢}�cÅ�¿rÃ Æ ­Ð¤¦z�¢¥¤¦­=¤@© Å½Æ ¨(­ Å ¢ Æ �(¤l�_z�¢]ã¡£­c@ç¢?©�ý���r¢�3Ì¢ Å ÃÆ£ Æ ¢?©¤ Å½Æ ¢�z�«f�¯­®©f¤0¤�¢�¾6«&¢?©�Ã�­Ð����¡£¢µ¾6«�¢¥¤¦Ã�¤¦Ã�¡£¢[��@$¤J©

§W¨(©;¤�­'z�¢]¡�Ã Æ ¢v¤�­¯Ã�«;�ªÃ�­¯¨(©F£ Æ ¢]©#�Êz�­Ð¤4Ã<­Ð¤�¤�¢?¡?Ñ�­ Å ­¯©f¤l�0¤¦Ã�¡£¢[��@{¨ªÈ夦¢µ¾6«�¢]©�Ã�­Ð�"�;¡�¢[�9zç¡£¢µ¾6«�¢¥¤¦Ã½¤x©yôÉÈå�¡£¢µ¾6«�¢¥¤¦Ã��ª¡�¡£­cÑ�¢[¤�Ã Æ �ªÃ�­Ð¤�©�¨@ÃÚ·;�ª¡�ì¨[ÈbÃ Æ ¢c� Å «�¡�¡£¢?©�ý�<¤¦Ã�¡£¢[��@ �ª©az$Ã Æ ¢ Å � Å½Æ ¢ã­®©az�­ Å �ªÃ�¢[¤Ã Æ �[ì­®Ãh£�­c�=�¶;¢l�RÈ�«f�=� Æ ­¯Ã»ÞÉ­¯©Ý�ª©�¨@Ã Æ ¢?¡ Å � ÅÇÆ ¢ö¤¦¢}¤7@ç¢?©�ÃJß½¿è� Å � Å½Æ ¢?êᤦ¢?©â¤¦­¯Ã�­=Ñ�¢Õ¤ Å½Æ ¢�z�«)�¯¢?¡v£�­=�c�q¤@­=Ñ�¢ Æ ­c¤ Æ ¢]¡b·�¡�­¯¨(¡�­¯ÃgÅã¨vÃ Æ �ªÃU¡�¢�¾�«�¢[¤¦Ãí¨"Ñ�¢]¡rÃ Æ ¢�©�¢}â�ÃW¤¦¢µ¾6«�¢]©�Ã�­Ð�"��¡£¢µ¾6«�¢¥¤¦Ãj­¯©0Ã Æ ¢0� Å «�¡�¡£¢?©�ý�Õ¤¦Ã£¡�¢[�"@­ÞE£ Æ ­ Å½Æ £�­c�=��¨(©f�cÅt¶;¢Õ�·;�[¡£Ã£­Ä�"� Æ ­®Ã«�©)�¯¢[¤�¤�Ã Æ ¢Æ·&¡£¢�È�¢?à ÅÇÆ ­¯©f¤l� Šã­=Ñ�­¯ÃgÅ0­Ä¤åÈá�ª¡�¨@«�Ã?·â� Å ­®©f¤0Ã Æ ¢l¤�¢?¡?Ñ�­ Å ­®©f¤v¨ªÈí¡£¢�¾�«�¢[¤�ý¤wßw©W�yÑ�¢?©ç­DÈ�"�c�;Ã Æ ¢Õ¤¦¢ Šã¨(¡Ï¤rÈ�¨(¡v¶;¨(Ã Æ ¡�¢�¾6«&¢[¤¦ÃϤU�ª¡�¢Ú·�¡£¢¥¤¦¢?©�ÃU­¯©<Ã Æ ¢ Å � ÅÇÆ ¢�¿(Ã Æ ¢?¡£¢�­Ð¤U©�¨ª£��}ÅRÈ�¨@¡Ã Æ ¢ Å � ÅÇÆ ¢�@ç¨�z�¢}�ã¨0­®©az�­ Å �ªÃ�¢¬Ã Æ �ªÃ��v¡£¢�¾�«�¢[¤�íФv·;�ª¡�Ã�¨ªÈjÃ Æ ¢ç� Å «�¡£¡�¢?©�ÃÏ�0¤¦¢�¾�«�¢?©�ã­Ä�"�;¤�ã¡�¢[�"@f�[©az$¤ Æ ¨@«f�'z<Ã Æ ¢?¡�¢�È�¨(¡�¢Ú¶;¢¤(­cÑ�¢?© Æ ­=¤ Æ ¢?¡h·&¡£­¯¨@¡£­®Ã4ÅÖ©h¹ Æ ­Ð¤�­Ð¤��[©à�ª¡£Ã�­4Èá� Šì¨[ÈbÃ Æ ¢º¤¦­=@<«f�Ä�ªÃ£¨@¡��ª©az�z�¨�¢[¤�©�¨(Ã�©&¢ Å ¢[¤�¤£�ª¡�­=�cÅç¡£¢Jò⢠ŠÃÕ�Å ¨7@d@ç¨(©pz�¢[¤�­=¤@© Å½Æ ¨@­ Å ¢¬È�¨@¡ Å «�¡£¡�¢?©�ÃØz�­Ð¤gÃFz�¡�­=Ñ�¢ Å ¨@©�Ã�¡£¨7�=�¯¢]¡½¤J©3J¹ Æ ¢ç¢}â�·;¢?¡£­c@ç¢?©�ý¤¬¨@© Æ ¨�¤�ãêE¶;�(¤�¢�z °  v¹��N¤ ÅÇÆ ¢�z�«f�®­¯©f¤F¤(­cÑ�¢?©�­®©ñ¤¦¢ Šã­¯¨@©½±�©¯À7©Õ¥�z�¨�©�¨@Ãã¢}â Æ ­c¶�­¯ÃÃ Æ ¢d¶;¢ Æ �}Ñ�­®¨(¡�z�­Ä¤ Å «â¤£¤¦¢µzù��¶;¨"Ñ�¢Ö©$¬1�=� Å ¨9@d·;�[¡£­Ä¤¦¨(©â¤Æ¶;¢?Ãg£¢?¢]© °  v¹��ì�"�=¤@¨(¡�­¯Ã Æ @$¤R­®©�Ã Æ �[Ã<¤¦¢ Šã­¯¨@©¡£¢�È�¢?¡¬Ã�¨$¢}â.·;¢?¡�­=@ç¢]©�ÃϤ�Ã Æ �ªÃ�«;¤�¢�z�­Ð¤gÃ�¤1£�­¯Ã Æ ¨(«�à Š¨9@d@$�[©azF¾6«&¢?«�¢?­®©f¤f©¦¬�¤�©�¨(Ã�¢�z#­¯©à¤�¢ Šã­®¨(© ¯ ©¯À7©Õ¥�¿¢}â�·;¢?¡£­c@ç¢?©�ý¤�«;¤¦­®©f¤�z�­Ð¤gÃ�¤v£�­¯Ã Æ ¨(«�à Š¨9@p@$�ª©azʾ�«�¢?«&¢?­¯©f¤l���Ф¦¨0«â¤¦¢�¨@©�ê�¶;¨è�ª¡wz×z��ªÃÏ� Å � Å½Æ ¢[¤y£�­®Ã Æ ¨@©�¢¡£¢¥�9zñ¤¦¢}¤7@ç¢?©�ÃdÞá�ª©az�¨(©&¢_£�¡£­®Ã£¢$¤�¢}¤9@î¢?©�Ãxßw©�«�­¯Ã Æ ¨(©f�cÅ�¨(©�¢$¡�¢[�9z ¤¦¢}¤7@ç¢?©�Ã?¿U���=��¡�¢[�9z Æ ­®Ã½¤ã¨ Å?Å «&¡£�­¯Ã Æ ­¯©ðÞ�¨(¡�©�¢[�[¡JßbÃ Æ ¢$� Å «�¡£¡�¢?©�ý�0¤¦¢µ¾6«�¢]©�Ã�­Ð�"� ¤¦Ã�¡£¢[��@�©Kì�MLj±��$�j� ål�;�ñ�ñ���rþõç��j´��r´ON´��r²����

¹ Æ ¢à�"@î¨(«�©�Ãw¨[Ⱥ�µÑ@�[­=�Ð��¶f�¯¢×@$�ª­®©¿@ç¢}@ç¨@¡?Å𶸨@«�©az�¤çÃ Æ ¢_·;¢?©az�­¯©f¤�¡�¢�¾�«�¢[¤¦Ãp¾�«�¢?«�¢×�¯¢?©f¤@Ã Æ È�¨@¡Æ ¨è¤¦Ã£êE¶;�@¤¦¢�z÷¤ Å½Æ ¢�z�«)�¯¢?¡Ï¤J© ° ­=@ç­c�Ð�[¡?�=Åè¿UÃ Æ ¢c�"@î¨(«�©�Ãw¨[Èv¨(©&ê�¶;¨��[¡wz Å ¨(©�ã¡�¨9�c�¯¢?¡�@ç¢}@<¨(¡;Å$¶;¨(«&©az�¤wÃ Æ ¢Å ¨7@d@$�ª©Iz�¾6«�¢]«�¢d�¯¢]©f¤(Ã Æ È�¨(¡º��z�­Ð¤gÃq©�¹ Æ ­Ð¤ã¤�¢ Å Ã�­¯¨(©�¢}â���@ç­¯©&¢[¤¬Ã Æ ¢ç¢�3Ì¢ Å ÃϤR¨ªÈ»�¯­c@ç­¯Ã�¢�z Å ¨9@d@$�[©az¾�«�¢?«�¢¦�¯¢]©f¤(Ã Æ ¤¨(©Èz�­Ð¤gÃ�êE¶;�(¤�¢�z Å ¢?©�ã¡Ï�"�¯­cî?¢�z<¤ Å½Æ ¢�z�«)�¯­¯©)¤f©�r­=¤@«�¡£¢¥¤ ' © 5 ì ' ©®À}¥$·�¡�¢[¤¦¢]©�Ã�@ç¢[�[©ù¡�¢[¤4·;¨@©;¤¦¢cã­=@î¢[¤RÈ�¨(¡�·;¨(­¯©�ý¤<�"�®¨(©f¤�Ã Æ ¢ �?Ã�©�¢?¢[¤�� ¨[ÈvÃ Æ ¢c­¯©�êz�­cÑ�­Äz�«;�"��¡�¢[¤4·;¨@©;¤¦¢cã­=@î¢ Å «�¡;Ñ�¢[¤öÈ�¨@¡é§Wêáë�Ó¦ÓÚ  �ª©Iz °  §]¹��b©]¹ Æ ¢F¶;�ª¡;¤(¡Ï�"· Æ ¤ç­®© Å �¯«Iz�¢Fz��[ý� È�¨@¡ U¡£¢[¤�¢?¢}Ã��ª©azÍ��«f�=� Å ¨9@d@Ý�ª©az½¾�«�¢?«&¢ Å ¨(©�ãa¤(«�¡Ï�ªÃ�­¯¨(©â¤´£�­¯Ã Æ @Ý�"â�­=@0«f@ Å ¨9@d@Ý�ª©azð¾6«&¢?«�¢F�¯¢?©)¤(Ã Æ ¤Þ��Ä�"¶;¢}�®¢�zù§�§¦ß�¨[È0À ' ¿�À}¥ 9 ¿�[©az�­¯©.ãâ©�­¯ÃgÅ�©×¬É@$��â�­c@w«f@á¾�«�¢?«�¢p�¯¢?©f¤@Ã Æ ¨[È0À ' ­Ð¤¦Ñ�­Ä¤¦­=¶)�=Åद«)¶¸¨7·�ã­®ê@$����È�¨(¡¦@ç¨�¤�ì¨[ÈbÃ Æ ¢0Ã�¡½� Å ¢@P[¤ ÅÇÆ ¢µz�«f�¯¢]¡ Å ¨9@�¶�­¯©â�ªÃ£­®¨(©;¤x©Ú��¨(¡ª�&��ͪÎ�»½¿WÓÕÔ'�ÇÖEïhÂ]×�¿bÛ���Ü�»x�Ç¿Ì�ª©IzöïÕ»�À&¾��ÇÞ�¿��@$�"â�­=@0«f@о6«&¢?«�¢F�¯¢?©)¤(Ã Æ ¨[È<À}¥ 9 ¤@¢?©�¢?¡Ï�"�=�cŽ·�¡�¨"Ñ�­'z�¢[¤Æ·;¢?¡�È�¨(¡?@Ý�ª© Å ¢$¢�¾�«�­cÑ(���¯¢?©�Ãvã¨��ª© ­¯©.ã;©&­¯Ã£¢¾�«�¢?«�¢Ú�®¢?©f¤@Ã Æ ©Wk#¢[�[©ç¡£¢¥¤4·;¨(©;¤�¢ãÃ�­=@ç¢[¤rÈ�¨@¡<¹»½¼¯¼D¾l�ª©az_�ÌØ?Ô¯Ö]Ùq�$­¯© Å ¡�¢[�(¤�¢Ú¶�Å´�®¢[¤£¤WÃ Æ �[© ¯.Ò £ Æ ¢?©$Ã Æ ¢@$��â�­c@w«f@ Å ¨7@d@$�[©azd¾�«�¢?«�¢Ú�®¢?©f¤@à ÆcÅÇÆ �ª©f¤@¢[¤�È�¡£¨7@{­¯©.ãâ©�­¯ÃgÅ<ã¨cÀ}¥ 9 ©b¹ Æ ¢ã¤�­¯©f¤7�¯¢v¢}â Å ¢}·�Ã�­¯¨@©çã¨0Ã Æ ¢�"¶;¨�Ñ�¢�¨9¶;¤�¢?¡?Ñ@�ªÃ�­¯¨@©;¤�­Ä¤ß§Wêáë�Ó¦Ó» 8¤ Å½Æ ¢�z�«)�¯­¯©)¤�¨ªÈvïÕ»�À&¾��ÇÞ�£�­¯Ã Æ Ã Æ ¢Õ å¡�¢[¤¦¢]¢}Ã�­®©f¤ Å ¨7@d@$�[©azt¾�«�¢?«�¢]­¯©f¤Å ¨@©.ãa¤(«&¡½�ªÃ�­¯¨@©�©º¹ Æ ¢×@ç¢[�[©ù¡�¢[¤4·;¨@©;¤¦¢�Ã�­=@ç¢d@î¢[�(¤�«�¡£¢�zðÈ�¨@¡wÃ Æ ­Ð¤ Å ¨9@�¶�­®©;�ªÃ�­¯¨(©�¢}â Å ¢?¢�z�¤çÀ�¤�¢ Å ¨@©azÞÉ­¡© ¢�©®¿��w¤��ªÃ£«&¡½�ªÃ�¢�zÇ£b¨(¡;Ã.�®¨��9zaßw©¹ Æ ¢v�Ð�@¤¦Ã�È�¢}£$¤@¢?©�¢?¡Ï�ªÃ�­¯¨(©â¤Ò¨[È ° § ° ô�z�­Ð¤gÃ�¤q·�¡�¨�Ñ�­Äz�¢v¾�«�¢?«�¢]z�¢}·&Ã Æ ¤�¨ªÈâ�ªÃ �¯¢[�@¤¦ÃWÀ ' ¿9£�­®Ã Æ ¤¦¨7@ç¢vz�­Ä¤4Ã&¤¾�«�¢?«�¢?­®©f¤$�@¤Æ@$�[©.Åc�(¤ '"¯ ¡£¢µ¾6«�¢¥¤¦Ã½¤RQ ° ¢[�"¤ ® ²@S¡© ° ­¯© Å ¢0Ã Æ ¢ ° § ° ô�ꡥǷ�¡�¨(Ã�¨ Å ¨9�v·�¡�¨"Ñ�­'z�¢[¤¦¥9± ' «�©�­Ä¾6«�¢Å ¨7@d@$�ª©IzYÃÏ�"¤�¤TQ ° § ° ô ® ²�S�¿;�Ê@$��â�­c@w«f@ Å ¨9@p@$�ª©az�¾�«�¢?«�¢¦�¯¢]©f¤(Ã Æ ¨[È�À}¥ 9 ¤¦¢]¢}@$¤b¾�«�­®Ã£¢v¡£¢[�@¤¦¨@©;�"¶f�®¢È�¨(¡�È�«�Ã�«�¡£¢Ú¤@¢?©�¢?¡Ï�ªÃ�­¯¨(©â¤�¨[È]z�­Ð¤gÃ�¤x©

UWV�)� �70 ���(5$3���0��$� =��7X���Y2����?.�CY W�Z�?%+�0�3�/�[%]\�%+��$^%+;�$� X70 �4Z%'712�����4_��)� ` ?!E%��?�=��CY"�$� �C_ ����1%'�����+�a�+6b70 �-/.� �(0�9(?�0)� �2�.�$� �70(���YC_�#2# �7��[2���(�:Y2#7���\� �(]�

Page 123: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(À >

C-LOOKc SPCTFd C-LOOKc SPCTFdScheduling Algorithme

0

50

100

150

200M

ea

n R

esp

on

se T

ime

(m

s)

f CQ = 16gCQ = 128gCQ = Infinityg

Preseekh Fulli

°�±É² jj³ª´Ok�µmlÌ·0¹»½¼®¼D¾(¿jÀ@npo#qªÁ0 rYsGt(¨@¡£­®Ã Æ @Ñ r¢?¡�È�¨(¡?@Ý�ª© Å ¢�È�¨(¡Yu¬­^v�¢]¡£¢?©�Ã�§W¨9@d@Ý�ª©azxw�«�¢]«�¢vë�¢?©yt@Ã Æ ¤

C-LOOKc SPCTFd C-LOOKc SPCTFdScheduling Algorithme

0

10

20

30

40

50

Me

an

Re

spo

nse

Tim

e (

ms)

CQ = 16gCQ = 128gCQ = Infinityg

Preseekh Fulli

°�±É² jj³[´zk�µG{�·_|~}�ͪÎ�»½¿jÀ@n3�@qªÁºÂ�r_sBt(¨@¡£­¯Ã Æ @Ñ r¢?¡¦È�¨@¡?@$�[© Å ¢�È�¨(¡�u¬­pvÌ¢?¡�¢?©�ì§W¨9@p@$�ª©az�w¬«&¢?«�¢lë�¢?©yt@Ã Æ ¤

Page 124: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(À@À

C-LOOKc SPCTFd C-LOOKc SPCTFdScheduling Algorithme

0

10

20

30

40

Me

an

Re

spo

nse

Tim

e (

ms)

CQ = 16gCQ = 128gCQ = Infinityg

Preseekh Fulli

°�±É² jj³[´zk�µG��·vÓÕÔA�ÇÖ0�Y�]×�¿R�Mn3qªÁ0Â[rYsGt(¨@¡£­®Ã Æ @  r¢?¡�È�¨(¡?@Ý�ª© Å ¢àÈ�¨(¡�u¬­pvÌ¢?¡�¢?©�Ã�§W¨7@d@$�[©az�w�«�¢?«�¢ë�¢?©yt(Ã Æ ¤

C-LOOKc SPCTFd C-LOOKc SPCTFdScheduling Algorithme

0

10

20

30

40

Me

an

Re

spo

nse

Tim

e (

ms)

CQ = 16gCQ = 128gCQ = Infinityg

Preseekh Fulli

°�±É² jj³[´zk�µÉ¶8��·�|¸Ø?Ô¯Ö?Ù�|;¿��Mn3qªÁ0Â[r_sBt(¨@¡£­¯Ã Æ @  r¢?¡¦È�¨@¡?@$�[© Å ¢�È�¨(¡�u¬­^vÌ¢?¡£¢?©�Ãð§W¨7@d@$�[©az�w�«�¢?«�¢ë�¢]©yt(Ã Æ ¤

Page 125: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(ÀZ�

C-LOOKc SPCTFd C-LOOKc SPCTFdScheduling Algorithme

0

10

20

30

40

50M

ea

n R

esp

on

se T

ime

(m

s)

CQ = 16gCQ = 128gCQ = Infinityg

Preseekh Fulli

°�±�² jr³[´zk�µ�¶;¶¸·ºÛa�£Ü�»��½¿�ÀEn��[Á0 r_sGt@¨(¡�­¯Ã Æ @{ r¢]¡¦È�¨(¡;@$�ª© Å ¢¬È�¨(¡Yu�­pvÌ¢?¡£¢]©�Ã�§W¨7@d@$�ª©Iz�w�«�¢?«&¢ãë�¢]©yt(Ã Æ ¤

C-LOOKc SPCTFd C-LOOKc SPCTFdScheduling Algorithme

0

20

40

60

80

100

120

Me

an

Re

spo

nse

Tim

e (

ms)

f CQ = 16gCQ = 128gCQ = Infinityg

Sa

tura

ted

Sa

tura

ted

Preseekh Fulli

°�±É² jj³[´zk�µÉ¶�ÊÌ·��Õ»?�&¾�ÇÞ�¿<À@n��[Á0Â[r_sBt(¨(¡�­¯Ã Æ @  j¢?¡¦È�¨@¡?@$�[© Å ¢ðÈ�¨@¡�u¬­pvÌ¢?¡�¢?©�Ã�§W¨7@d@$�[©az�w�«�¢?«�¢ë�¢]©yt(Ã Æ ¤

Page 126: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(ÀZ�

�¬¨�¤�ãê1���(¤¦¢µz u¬­Ä¤W��ê?���@¤¦¢�z�6Å ��s®¢ §Wêáë5������n4§H��nD§�� �  ß§��a��n4§H��n4§�� §Wêáë5����� �  §��a�

��¡½� Å ¢ �;� Å Ã�¨(¡ §aw���� §aw���À §aw���À��E� §aw��ôÀ��E�§W¢�sGs®¨ À@n^o�q ¶M  ��µB ~� ¶;¶8k�µml;Ê À/¡&À@n3¢@¢ À@À��Mn3�£o� ©;����¢ À@n3�@q Êy¤�µAl;Ú Ê¥kÒµB�   �£o¦n��@q �EqMn^o�Àr�­¯¡£ê1��¤W§ �8n�q �E�Mn3�@¢ �@�Mn3q@¨ Ê¥��µÐÚ¸Ê Êy �µÐÚ;Ê��Å ­¯ê1� � �8n�q Êy��µBk ¤ �@�Mn3¨@� �@�8n©¡� ¶M{�µAl¥���¡wz�¢]¡ ÀEn�� �E�Mn3¢@� �@�Mn3¢@¨ Ê¥¤�µÐÊyk Êy��µ�¶;¶��¢Zª¸¨@¡£Ã ÀEn��  ~��µÐÚ̶ ¡¢Mn3��À � �ªÃ£«&¡½�ªÃ�¢�z ¤~��µ�¶8k

« �¬� U¡£¢¥¤¦¢?¢��$§W¨9@p@$�ª©az�w¬«&¢?«�¢?­®©yt

�¬¨�¤�ãê1���(¤¦¢µz u¬­Ä¤W��ê?���@¤¦¢�z�6Å ��s®¢ §Wêáë5������n4§H��nD§�� �  ß§��a��n4§H��n4§�� §Wêáë5����� �  §��a�

��¡½� Å ¢ �;� Å Ã�¨(¡ §aw���� §aw���À §aw���À��E� §aw��ôÀ��E�§W¢�sGs®¨ À@n^o�q ¶M��¶;µB{~k À@À�¨8npo�� À��E�Mn3¨@� ¶8� ��µG �Ú� ©;����¢ À@n3�@q ʸÊ̵Bk { �@¨Mn3¢�¡ �@q8npo�¢ ʸÚ̵�¶;¶r�­¯¡£ê1��¤W§ �8n�q �E¢Mn^o�¨ �@�Mn3q@¨ Ê¥k�µB¤~{ Ê�¶;µB¤ ���Å ­¯ê1� � �8n�q ÀZ�Mn­¡� �@�Mn3¨@� ¶8k�µAly� ¶M¤�µB  ���¡wz�¢]¡ ÀEn�� �E�Mn®À�¨ �@�Mn3¢@¨ Ê̶;µBk~¤ ¶M{�µB¤�Ú��¢Zª¸¨@¡£Ã ÀEn�� �E¢Mn3�@¨ ¡¢Mn3��À ¤ ¤�µB¤ Ú Êy �µÐÚ̶

«�® ¬���«ysGsU§W¨7@d@$�ª©Iz�w�«�¢?«&¢?­¯©yt

¯b�y°j�É´±k�µ�¶¸·ßk#¢[�ª©O��¢[¤Wª;¨(©â¤¦¢��­c@ç¢[¤ « @ݤ'¬rÈ�¨@¡³²´��¢¥�(¤¦¨@©;� ® s¯¢�µç§W¢?©�㡽��s¯­B¶?¢�z ��Å½Æ ¢�z�«ys¯¢?¡Ï¤·l�;�ñ�r��³[±�¸?�;�º¹<±Ð��� �����j´�þ5jj�ɱ��j²ð���<���j´z»c�~¸��

� Æ ¢ç¨Eª�ã­c@$��s=s®¨ Å �ªÃ�­¯¨@© È�¨@¡0� Å ¢?©�Ã�¡½��s¯­G¶]¢�z#¤ ÅÇÆ ¢µz�«ys¯¢]¡�­Ð¤ Å ¨7@¼ªys¯¢]ã¢�sB½_z�¢�ª;¢?©az�¢?©�Ãv¨(©�Ã Æ ¢R¾¨(¡���ês¯¨è�9zñ�ª©Izø¤W½&¤¦Ã�¢}@ Å ¨@©M¿ t@«�¡½�[ã­¯¨@©�¿ ® «&Ã<¤¦¨9@t(¢?©&¢?¡½��s�¨ ® ¤�¢?¡]§@�ªÃ�­¯¨@©;¤ Å �ª© ® ¢Ç@Ý�9z�¢ ® �(¤¦¢µzù¨(©ñÃ Æ ¢¢�À8ª;¢?¡£­c@ç¢?©�ý��sb¡£¢[¤�«ys¯ÃϤ/nÁ�r� ® s¯¢�¨8n¯Àzs®­Ð¤�ý¤wÃ Æ ¢�@ç¢[�[©ø¡£¢¥¤Wª;¨(©;¤�¢ðÃ�­=@碥¤RÈ�¨(¡çÃ Æ ¢à¤¦­BÀÂ�� 2�ª©azÂu�Ãߧã¡Ï� Å ¢¥¤ö«â¤¦­¯©¥t#¢?­Bt Æ Ãtz�­pvÌ¢?¡£¢]©�à Š¨7@ ® ­®©;�ªÃ�­¯¨@©;¤¬¨ªÈ Å ¢?©�Ã�¡½��s¯­G¶]¢�z�¤ Å½Æ ¢�z�«¥s¯¢?¡Ï¤��ª©az Å ¨9@d@Ý�ª©az±Ä�«�¢?«�¢]­¯©ytÅ ¨@©M¿ t(«&¡½�ªÃ�­¯¨@©;¤/nO� Æ ¢[¤�¢ Å ¨7@ ® ­¯©;�[ã­¯¨@©;¤�¡£¢�ª&¡£¢[¤�¢?©�ÃŲ£¡£¢¥�(¤¦¨@©;� ® s¯¢�µ#­c@¼ªys¯¢C@w¢?©�ÃÏ�ªÃ�­¯¨(©â¤�¨[È Å ¢?©�㡽��s¯­B¶?¢�z¤ Å½Æ ¢�z�«ys¯­®©yt0¤�ª¸¢ Å ­p¿ Å ��sGsB½wÃ�«�©�¢�zçÃ�¨ç¤�¢?¡]§�­ Å ¢ö��sGsj¤�­GÀ<ã¡Ï� Å ¢[¤�n

��¨(¡ Å ¨(©M¿ t@«�¡½�[ã­®¨(©;¤,¾�­®Ã Æ  U¡£¢¥¤¦¢?¢�� Å ¨9@d@$�[©az±Ä�«�¢?«�¢?­®©yt�¿jÃ Æ ¢<¨@ª&ã­=@Ý��s ÅÇÆ ¨(­ Å ¢ãÈ�¨(¡ Æ ¨è¤¦Ã£ê ® �@¤¦¢�z§�¢?¡Ï¤¦«;¤�z�­Ä¤W��ê ® �(¤¦¢µz#¤ Å½Æ ¢�z�«ys¯­®©yt0­Ð¤�¢�§�¢?©ysB½<¤Wªys®­¯ÃÈ�¨@¡¬Ã Æ ¢0¤�­GÀçÃ�¡½� Å ¢[¤ « ¤¦¢?¢vÃÏ� ® s®¢,¨8n¯À]�£¬+nÆr Æ ¨è¤¦Ã£ê ® �@¤¦¢�z¤ Å½Æ ¢�z�«ys¯¢?¡�¾¨@¡]�&¤ ® ¢[¤�ÃYÈ�¨@¡à¹»½¼¯¼D¾��[©azÇ|b}&ͪÎ�»+È��ðz�­Ä¤W��ê ® �@¤¦¢�z ¤ Å½Æ ¢�z�«¥s¯¢?¡�¾¨(¡���¤ ® ¢[¤¦Ã0È�¨(¡çÓÕÔA�½Ö0�Y�]×�ª©Iz8Ûa�£Ü�»'�'Èí�ª©azðÈ�¨(¡R|ÌØ?Ô¯Ö?Ù�|��[©azº��»1��¾�½Þ�¿ÒÃ Æ ¢ ® ¢¥¤¦Ã0¤ ÅÇÆ ¢�z�«ys®¢?¡�­Ð¤ Æ ¨�¤�Ã£ê ® �(¤�¢�zðÈ�¨(¡<§Wê�ë5�[���f�ª©azz�­Ä¤W��ê ® �@¤¦¢�zðÈ�¨@¡ �  §��a�>nH�¬¨�¤�Ã£ê ® �(¤�¢�zñ¤ Å½Æ ¢�z�«¥s¯­¯©¥t#¡£¢µz�« Å ¢[¤vÃ Æ ¢$Ã�¨(ý��s��"@ç¨@«�©�Ãã¨ªÈ Å ¨7@d@$�ª©Iz��ª©azÅ ¨7@¼ªys¯¢]ã­¯¨@©ç¨�§�¢?¡ Æ ¢[�9z ® ½ Å ¨(© Å �ªÃ�¢?©;�ªÃ�­¯©ytݤ¦¢�Ä�«�¢?©�ã­Ä��s�¡�¢�Ä�«�¢[¤¦ÃϤ/nau�­Ð¤W��ê ® �(¤�¢�z#¤ ÅÇÆ ¢µz�«ys¯­®©yt0¢?© Æ �ª© Å ¢¥¤

Page 127: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(À�¡

­¯©�ã¢]¡£ê�¡£¢�Ä�«�¢[¤�à Š¨(© Å «�¡£¡�¢?© Å ½�Ã Æ ¡£¨@«yt Æ s¯¨@©yt(¢]¡r¨@©�ê ® ¨è�ª¡wz Å ¨9@d@Ý�ª©azDÄ�«�¢?«&¢[¤ « ¢[¤Wª;¢ Å ­Ð��sBsG½¬È�¨@¡ �  §��a�`¬´n��«�¡£Ã Æ ¢?¡;@ç¨(¡�¢�¿ �  ß§��a�à¤ Å½Æ ¢�z�«ys¯­®©yt¬­Ä¤�@ç¨@¡£¢�� Å]Å «�¡½�[ã¢a¾ Æ ¢]©�ª¸¢]¡¦È�¨(¡;@ç¢�zl�ªÃWÃ Æ ¢1z�­Ð¤W�Ì¿��(¤ Æ ¨è¤¦Ã£ê ® �@¤¦¢�z¤ Å½Æ ¢�z�«ys¯¢?¡Ï¤Ü@<«;¤¦ÃØz�¢[��s�¾�­¯Ã Æ «�©¥ª�¡£¢�z�­ Å ÃÏ� ® s®¢ ® «;¤1z�¢�sÄ�#½&¤��¥È�Ã�¢?¡�¤¦¢Zs¯¢ Å Ã�­¯©ytº�Y¡�¢�Ä�«�¢[¤¦Ãbã¨î¤¦¢?¡�§�­ Å ¢n

�¬¨�¤�Ã£ê ® �(¤�¢�z�¤ ÅÇÆ ¢µz�«ys¯­®©yt�ª;¢?¡¦È�¨@¡?@$�[© Å ¢0­=@Ū�¡£¨�§�¢[¤a¾ Æ ¢?©���«ysGs Å ¨9@d@$�[©azzÄ�«�¢?«&¢?­¯©yt$­Ä¤ö¢]©;� ® s®¢�z�¿® «�øz�­Ð¤���ê ® �(¤�¢�z�¤ Å½Æ ¢�z�«ys¯¢?¡Ï¤Étè�ª­®©�Ã Æ ¢×@ç¨�¤�ÃYÈ�¡�¨9@ Ã Æ ¢#«¥ªyt(¡Ï�9z�¢à­¯©èz�­Ð¤�� Å ¨(©�ã¡£¨EsGs®¢?¡ Å ¨9@¼ªys®¢�À�­¯Ã�½@n�j� ® s®¢�¨8n¯À ® ¤ Æ ¨�¾�¤çÃ Æ �ªÃ×z�­Ä¤W��ê ® �@¤¦¢�z �  §��a�{¤ ÅÇÆ ¢µz�«ys¯¢]¡½¤ãÈ�¨(¡ ¹»½¼¯¼ï¾��ª©az�|~}�ͪÎ�»$�[©az §Wêáë5�[���¤ Å½Æ ¢�z�«ys¯¢?¡Ï¤�È�¨(¡[|ÌØ?Ô¯Ö?Ù�|c�[©azÊ��»1��¾�½Þ;¨(«�Ã�ª¸¢]¡¦È�¨(¡;@pÃ Æ ¢?­¯¡ Æ ¨�¤¦Ã�ê ® �(¤¦¢µz Å ¨(«�©�ã¢]¡]ª;�[¡£Ã½¤a¾ Æ ¢?©Ë��«ysGs Å ¨7@çê@$�[©az�Ä6«�¢]«�¢?­¯©¥t0­Ð¤¢?©;� ® s¯¢µz�È�¨(©ysB½�§Wê�ë5�[���ô¤ Å½Æ ¢�z�«¥s¯­¯©¥tãÈ�¨(¡î¹»½¼¯¼D¾0�[©azÊ|b}�ͪÎ�»�­Ä¤ ® ¢[¤¦ÃYª;¢?¡¦È�¨@¡?@ç¢�z® ½çÃ Æ ¢ Æ ¨è¤¦ÃZn

}YÌ�~>Ì?Í ÎDÏYÐ�ÐÒÑ�ÓYÔ��yÕ=Ö �R×yØHÙ�ÕXÔ� Æ ­Ð¤b¤¦¢ Šã­¯¨@©ç¢�À&�"@ç­®©�¢[¤rÃ Æ ¢Dª;¢?¡�È�¨(¡?@Ý�ª© Å ¢�¨ªÈ�z�­Ð¤W��ê ® �(¤�¢�z Å ¢?©�㡽��s¯­B¶?¢�z0¤ Å½Æ ¢�z�«ys¯­®©yt�È�¨(¡Ã Æ ¢[ÚR§��

ã¡Ï� Å ¢¥¤/nº��©ysB½ Æ �ª¡wz8¾��ª¡�¢?êá¤Wª;¢ Å ­^¿ Å ­¯©�È�¨@¡?@$�[ã­¯¨@©�­Ð¤v«;¤¦¢µz ® ½�Ã Æ ¢$¤ Å½Æ ¢�z�«ys¯¢?¡]¿ ® «&à ® ¨@Ã Æ ¤¦« ® ¤�½�¤�ã¢}@�ª©Iz#¤W½&¤¦Ã�¢}@ « ­?n ¢¦n¯¿���ªyª¥s¯­ Å �ªÃ£­®¨(©�êá¤Wª;¢ Å ­p¿ Å ¬�@ç¢?Ã�¡£­ Å ¤��[¡£¢l¡£¢�ª;¨(¡�ã¢�zbn� ´���jj´��;�[±���������j´�þXjr��±��r²

��¨(¡»z�­Ð¤���¤a¾�­¯Ã Æ @$��À�­c@w«f@ Å ¨9@p@$�ª©azÅÄ6«�¢]«�¢[s¯¢?©yt@Ã Æ ¤�¨ªÈÕÀZ�@��¿ ¤¦¢�Ä�«�¢?©�ã­Ä��s�¤ ÅÇÆ ¢�z�«ys®­¯©yt0¨[È¡�¢[�9z&¤�ª©Iz~P?¨@¡,¾�¡£­®Ã£¢[¤��#vÌ¢ Šý¤�Ã Æ ¢�ª;¢?¡�È�¨(¡;@$�ª© Å ¢t@ç¢?Ã�¡£­ Å ¤�È�¨(¡�Ã Æ ¢¼|bÛE}£��Ü�»�}�¾b¨(¡��Ms®¨��9z ® ½zs®¢[¤£¤�Ã Æ �[©ñÀ�ÝÅn��¨(¡0Ã Æ ¢ ¹W¾�_�b�Ç»]�+��¾¨(¡��Ms®¨��7z�¿¤�¨9@ç¢î¨ªÈÕÃ Æ ¢c��sBt(¨@¡£­¯Ã Æ @$¤v¢�ÀMª;¢?¡�­¯¢?© Å ¢ç��À+Þ8�Ýóz�¡£¨@ªñ­®©½@ç¢[�[©�¡£¢?ê¤Wª;¨@©;¤¦¢vã­c@ç¢[¤�¾ Æ ¢?©$¤ ÅÇÆ ¢�z�«ys®­¯©ytl¤¦¢#Ä6«�¢]©�Ã�­Ð��s¥¾�¡£­¯Ã�¢¬¡�¢�Ä�«�¢[¤¦ÃϤU­¯©Rs¯¨@t@­ Å ��sGsB½<�(¤ Å ¢?©az�­®©ytã¨@¡wz�¢?¡UÈ�¨@¡�z�­Ä¤W�&¤¾�­¯Ã Æ ��«ysGs Å ¨9@p@$�ª©azßÄ6«&¢?«�¢?­®©ytyn�� Æ ¢]¡£¢�È�¨@¡£¢�¿�Ã Æ ¢�¡�¢}@$�ª­®©�­¯©¥t�¢�ÀMª;¢?¡�­=@ç¢]©�ÃϤ㭯©�Ã Æ ­Ð¤ç¤�¢ Šã­®¨(©�«;¤�¢©�¨c¤¦¢#Ä6«�¢]©�Ã�­Ð��så¤ Å½Æ ¢�z�«ys®­¯©ytî¨@ª�Ã�­=@ç­B¶[�ªÃ�­¯¨(©â¤ßÈ�¨@¡ Å ¨@©M¿ t(«&¡½�ªÃ�­¯¨@©;¤�¾�­®Ã Æ  å¡�¢[¤¦¢]¢�� Å ¨7@d@$�[©azzÄ�«�¢?«�¢]­¯©yt�ª©Izù¤�¢�Ä�«�¢?©�ã­Ð��sb¤ Å½Æ ¢�z�«ys®­¯©yt$¨[È ® ¨(Ã Æ ¡£¢[�7z�¤0�ª©az�¾�¡�­¯Ã£¢¥¤ÕÈ�¨@¡ Å ¨(©8¿ t(«�¡Ï�ªÃ�­¯¨(©â¤É¾�­®Ã Æ ��«ysBs Å ¨9@d@$�[©azÄ�«�¢?«�¢?­®©ytyn­à

Kì�MLj±��Êjj� ·l�;�ñ�ñ���rþâáRjj´8jr´ON´��r²������¨(¡�À�êɫ⤦¢?¡õ�ª©azã�[êɫ⤦¢?¡�|bÛ@}£��Ü�»�}�¾¨@¡]�8s¯¨è�9z�¤�¿RÃ Æ ¢ Å½Æ ¨@­ Å ¢�¨[È�@$��À�­=@0«f@ Å ¨9@d@Ý�ª©azÂÄ�«�¢?«�¢

s¯¢]©yt(Ã Æ �#vÌ¢ Å ÃϤt@ç¢[�[©ð©�¨@©�ê Å ¨9@¼ª&«�ã¢<ã­c@ç¢[¤ ® ½Ês®¢[¤£¤vÃ Æ �[©÷À�ÝÅn±�r­Gt@«�¡£¢¥¤,¨Mn®À����[©azä¨Mn¯À�¡�¤ Æ ¨�¾KÃ Æ ¢@ç¢[�[©�¡£¢¥¤Wª;¨(©;¤�¢�ã­c@ç¢[¤;�ª©az¦@ç¢[�[©R©&¨(©�ê Å ¨9@Ū�«�ã¢WÃ�­=@ç¢[¤�È�¨@¡5¡@êÉ«;¤�¢?¡ Å ¨(©M¿åt(«�¡Ï�ªÃ£­®¨(©;¤X¾�­¯Ã Æ  U¡£¢[¤�¢?¢��Õ�ª©az��«ysGs Å ¨9@d@Ý�ª©az�Ä6«�¢]«�¢?­¯©¥t�¿(¡�¢[¤Wª;¢ Å Ã�­G§�¢�sB½n�k���À�­c@w«f@ Å ¨7@d@$�[©az,Ä�«�¢?«�¢as®¢?©yt@Ã Æ ¤U¨ªÈåÀ��E�0�ª©az0­¯©M¿â©�­¯Ã�½ª�¡�¨�§�­'z�¢�¢�Ä�«�­G§@��s®¢?©�Ã`ª;¢?¡�È�¨(¡;@$�ª© Å ¢v� Å ¡�¨�¤�¤���sGs ��sBt(¨(¡�­¯Ã Æ @$¤/nH��¢�z�« Å ­¯©ytlÃ Æ ¢»@$��À�­=@<«f@ÁÄ6«&¢?«�¢Ds®¢?©yt(à Æã¨cÀ�¨pz�¢�t(¡Ï�9z�¢¥¤_ª;¢?¡¦È�¨@¡?@$�[© Å ¢�È�¨(¡�Ã Æ ¢ºë��aÚ¬ê ® �(¤�¢�z#��sGt(¨@¡£­®Ã Æ @$¤�¿�­¯© Å ¡£¢[�@¤¦­¯©¥t´@碥�ª©$¡£¢[¤�ª;¨(©;¤�¢0ã­=@î¢[¤® ½é«¥ª�ã¨�ÀZ�£Ýf�[©az_@ç¢[�[©#©�¨@©�ê Å ¨9@¼ª&«�ã¢lã­=@î¢[¤ ® ½$«yª�Ã�¨��£ÝÅnDr @Ý��À�­=@0«f@æÄ6«&¢?«�¢,s®¢?©yt@Ã Æ ¨[ÈÕÀ�¨ª�¡�¨�§�­'z�¢[¤�@$�[¡]t(­®©;��sBsG½l¤¦«¥ª¸¢]¡£­¯¨@¡>ª;¢?¡�È�¨(¡?@Ý�ª© Å ¢WÈ�¨(¡WÃ Æ ¢�È�«ysBs¯ê���©&¨�¾as®¢�zMt@¢���sGt@¨(¡�­¯Ã Æ @$¤�¿@¾�­®Ã Æ @碥�ª©0©�¨@©�êÅ ¨7@¼ª�«�Ã�¢ãã­c@ç¢[¤1z�¢ Å ¡�¢[�(¤�­¯©ytÅs¯¢[¤�¤öÃ Æ �ª© À�ÝÅn �  H�a�rê ® �(¤�¢�zð��sGt@¨(¡£­®Ã Æ @ݤ��ª¡�¢³t@¡£¢?¢�z8½#­¯©à©;�[ã«�¡�¢<�ª©azÃ Æ ¢?¡£¢�È�¨@¡£¢ Æ ­Bt Æ sB½ç¤�«;¤ Å ¢Zª�ã­ ® s¯¢�Ã�¨w¡�¢�Ä�«�¢[¤¦Ãߤ¦ÃÏ�ª¡]§@�[ã­¯¨@©�n�ë�­c@ç­¯Ã�­¯©ytvÃ Æ ¢R©�«f@ ® ¢?¡W¨ªÈHª;¢?©az�­¯©yt0¡�¢�Ä6«&¢[¤¦ÃϤ§�­Ð¤¦­ ® s¯¢0Ã�¨�Ã Æ ¢Ý¤ Å½Æ ¢�z�«ys®¢?¡v¡£¢[¤�«ys¯ÃϤ�­¯©�­®© Å ¡£¢¥�(¤¦¢µz���t@¢?ê�¤�¢?©;¤�­¯Ã£­B§�­®Ã�½�¿�Ã Æ ¢?¡�¢ ® ½�¡£¢�z�« Å ­¯©yt$Ã Æ ¢¼ª;¨(Ã�¢?©�Ã�­Ð��sÈ�¨(¡Õ¤¦ÃÏ�ª¡�§(�[ã­®¨(©#¨[È Æ ­Gt Æ ª�¡£­®¨(¡�­¯Ã�½w¡�¢�Ä�«�¢[¤¦ÃϤ/n

�r­Gt@«�¡£¢¥¤�¨8n¯ÀZqé�[©az�¨Mn¯ÀZ¨xª�¡�¢[¤¦¢]©�Ã�Ã Æ ¢�ª;¢?¡¦È�¨@¡?@$�[© Å ¢�z��[ý�wÈ�¨(¡vÃ Æ ¢R�ªê�«;¤¦¢]¡³|bÛE}£��Ü�»�} Å ¨(©M¿ t@«�¡½�[êã­®¨(©;¤�nYr_t��[­¯©�¿Ì�´@$��À�­c@0«f@ Å ¨9@p@$�ª©azÅÄ6«�¢]«�¢,s®¢?©yt(Ã Æ ¨[È�À��E�³ª�¡£¨�§�­'z�¢¥¤çt@¨�¨�zÒª;¢?¡�È�¨(¡?@Ý�ª© Å ¢l� Å ¡£¨è¤£¤è+�� �-/.� W�Z�0�^%+$�(?��)� �2�.�$�����4H�'6¦70 �%�2�(���(y�3�@�?$�.E2� �2`6B�/7 é�.�$�$E����CYCD%+�E2=-/.� �.� �����4��?�/��êE4�.�71%+�0������(y����$3ëì6B��7 �?�/��(���(��0 ��E�?ë

*�����)D���0)� �7� ?!�"@ �7���C_ �����(�� í£������$� =��7�����;@ ��� ?ê@�9��(�4Z%'�3�� �2ç6B7��/Cä��)���(��/"�����CY��î�%'�������>���Y�0)���(X�?������ �!#�]�

Page 128: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(ÀZq

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2)ñ SPTFò ASPTF(6)ó SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

50

100

150

200

Mea

n R

espo

nse

Tim

e (m

s)

ö CQ = 16CQ = 128CQ = Infinity

« �£¬Æ÷#¢[�[©z��¢[¤�ª¸¨@©;¤¦¢T�­Gøç¢

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2)ñ SPTFò ASPTF(6)ó SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

ù CQ = 16CQ = 128CQ = Infinity

«�® ¬�÷#¢[�[©zÚ�¨(©�ê�§W¨@ø¼ª&«�ã¢��­Gøî¢

°�±É² jj³[´zk�µÉ¶8¤�·�|~Û@}£��Ü�»�}�¿�¡�ú�¤�¢?¡½¤� �6ÅÇÆ ¢µz�«ys¯­®©yt�r_sBt(¨(¡�­¯Ã Æ ø  r¢?¡�È�¨(¡�ø$�ª© Å ¢wÈ�¨(¡Åu¬­Ð¤���¤�¾�­¯Ã Æ U¡�¢[¤¦¢?¢Z�#§W¨@ø¼øÝ�ª©az¼w�«�¢?«�¢?­®©yt

Page 129: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(ÀZ¨

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

50

100

150

200

Mea

n R

espo

nse

Tim

e (m

s)

ö CQ = 16CQ = 128CQ = Infinity

« �£¬Æ÷#¢[�[©z��¢[¤�ª¸¨@©;¤¦¢T�­Gøç¢

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

ù CQ = 16CQ = 128CQ = Infinity

«�® ¬�÷#¢[�[©zÚ�¨(©�ê�§W¨@ø¼ª&«�ã¢��­Gøî¢

°�±É² jj³[´zk�µÉ¶8 �·�|~Û@}£��Ü�»�}�¿�¡�ú�¤�¢?¡½¤� �6ÅÇÆ ¢µz�«ys¯­®©yt�r_sBt(¨(¡�­¯Ã Æ ø  r¢?¡�È�¨(¡�ø$�ª© Å ¢wÈ�¨(¡Åu¬­Ð¤���¤�¾�­¯Ã Æ��«ysBsr§W¨Eø¼ø$�ª©Izxw�«�¢?«�¢?­®©yt

Page 130: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(À�o

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

100

200

300

400

Mea

n R

espo

nse

Tim

e (m

s)

ö CQ = 16CQ = 128CQ = Infinity

« �£¬Æ÷#¢[�[©z��¢[¤�ª¸¨@©;¤¦¢T�­Gøç¢

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

ù CQ = 16CQ = 128CQ = Infinity

«�® ¬�÷#¢[�[©zÚ�¨(©�ê�§W¨@ø¼ª&«�ã¢��­Gøî¢

°�±É² jj³[´zk�µÉ¶�ÚÌ·�|~Û@}£��Ü�»�}�¿Æ�Êú�¤�¢?¡½¤� �6ÅÇÆ ¢µz�«ys¯­®©yt�r_sBt(¨(¡�­¯Ã Æ ø  r¢?¡�È�¨(¡�ø$�ª© Å ¢wÈ�¨(¡Åu¬­Ð¤���¤�¾�­¯Ã Æ U¡�¢[¤¦¢?¢Z�#§W¨@ø¼øÝ�ª©az¼w�«�¢?«�¢?­®©yt

Page 131: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(ÀZ�

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

100

200

300

400

Mea

n R

espo

nse

Tim

e (m

s)

ö CQ = 16CQ = 128CQ = Infinity

« �£¬Æ÷#¢[�[©z��¢[¤�ª¸¨@©;¤¦¢T�­Gøç¢

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

ù CQ = 16CQ = 128CQ = Infinity

«�® ¬�÷#¢[�[©zÚ�¨(©�ê�§W¨@ø¼ª&«�ã¢��­Gøî¢

°�±É² jj³[´zk�µÉ¶8k�·�|~Û@}£��Ü�»�}�¿Æ�Êú�¤�¢?¡½¤� �6ÅÇÆ ¢µz�«ys¯­®©yt�r_sBt(¨(¡�­¯Ã Æ ø  r¢?¡�È�¨(¡�ø$�ª© Å ¢wÈ�¨(¡Åu¬­Ð¤���¤�¾�­¯Ã Æ��«ysBsr§W¨Eø¼ø$�ª©Izxw�«�¢?«�¢?­®©yt

Page 132: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À(ÀZ¢

Ã Æ ¢ç¡½�[©yt(¢ç¨[ÈÕ¤ Å½Æ ¢�z�«¥s¯­¯©¥t#��sGt@¨(¡£­®Ã Æ øݤ/nOû ©�ø$�[©M½ Å �@¤¦¢[¤�¿5ª;¢?¡�È�¨(¡]øÝ�ª© Å ¢pz�¢�t@¡½�7z�¢[¤�¾ Æ ¢?©�Ã Æ ¢¼ø$��À�ê­Gø<«yø Å ¨@ø¼øÝ�ª©az±Ä�«�¢?«�¢Rs¯¢]©yt(à ÆñÅÇÆ �ª©yt@¢[¤ãã¨c­¯©M¿;©&­¯Ã�½nO� Æ �ªÃ0­Ä¤�¿U­¯Ãv­Ä¤R¨ªÈ�Ã�¢?© ® ¢?ãÃ�¢?¡ã­DÈ�Ã Æ ¢$¤ Å½Æ ¢�z�ê«ys®¢?¡ Å ¨(©â¤¦­'z�¢?¡½¤¬¨@©ysG½$Ã Æ ¢�²]øç¨è¤¦Ã�¡£¢ Å ¢]©�ôµéÀZ�@�w¡�¢�Ä6«&¢[¤¦ÃϤ/na� Æ ¢]¡£¢0�[¡£¢0Ã�¾¨î�ª©&¨@ø$��s¯¨(«â¤çª;¨(­®©�ÃϤ�­®©#Ã Æ ¢t(¡Ï��ª Æ ¤åÃ Æ �ªÃ ® ¢¥�ª¡�È�«�¡£Ã Æ ¢?¡vz�­Ä¤ Å «â¤£¤¦­®¨(©�n9��¨(¡W§Wê�ë5�[���8¤ Å½Æ ¢�z�«ys¯­®©yt�¨ªÈäz�­Ä¤W�&¤ü¾�­®Ã Æ  U¡�¢[¤¦¢?¢Z� Å ¨@ø¼ø$�[©azÄ�«�¢?«�¢?­®©yt�¿�§Wêáë5�[���ô��ªyª;¢[�[¡½¤¬Ã�¨$� Å½Æ ­¯¢Z§�¢_ø<« Å½Æ ® ¢?ãÃ�¢?¡_ª;¢?¡�È�¨(¡�ø$�ª© Å ¢D¾�­¯Ã Æ �ª©c­¯©M¿â©�­¯Ã�¢ Å ¨@ø¼ø$�[©azÄ�«�¢?«�¢Ds®¢?©yt@Ã Æ nH��¨(¡ �y� �a�ñ¤ Å½Æ ¢�z�«ys¯­®©ytã¨[Èvz�­Ä¤W�&¤>¾�­¯Ã Æ ��«ysGs Å ¨@ø¼øÝ�ª©az�Ä�«�¢?«�¢]­¯©yt&¿ �y� �a�ñ��ªyª;¢[�ª¡Ï¤�Ã�¨� Å½Æ ­®¢�§�¢�¤¦«yª;¢?¡�­¯¨@¡aª¸¢]¡¦È�¨(¡�ø$�ª© Å ¢_¾�­®Ã Æ �,øÝ��À�­Gø0«yø Å ¨Eø¼ø$�ª©Iz�Ä6«�¢]«�¢Ds¯¢]©yt(Ã Æ ¨ªÈßÀ�¨8nHû © ® ¨@à ÆcÅ �@¤¦¢[¤�¿Ã Æ ¢¬©�«yø ® ¢]¡r¨[ÈY²£Ã½�@¤W�&¤]µ Å ¨@ø¼ª¥s¯¢?Ã�¢�z ® ¢�È�¨@¡£¢�Ã Æ ¢aª�¡£¨ Å ¢[¤£¤�êmý;¨�¾þøç¨�z�¢�s Æ ��s®Ã½¤U­Ð¤W� Šã«;��sGsG½�s®¨�¾¢?¡Zn5� Æ �ªÃ­Ð¤�¿�Ã Æ ¢Dª�¡�¨ Å ¢[¤£¤�¢[¤�¤¦­Bøw«¥sÐ�ªÃ�¢�z0­¯©çÃ Æ ¢ Æ ¨è¤¦Ãaøç¨�z�¢Zs�¢�À8ª;¢?¡£­®¢?© Å ¢�z<�ª©$«�©�«;¤�«;��s̨(¡wz�¢?¡£­®©yt<¤¦« Å½Æ Ã Æ �ªÃ�Ã Æ ¢øç¨�z�¢Zs Æ �9zçã¨O²½� ® ¨@¡£Ã+µ0¢[�[¡]s¯­®¢?¡UÈ�¨(¡bÃ Æ ¢[¤�¢v¤¦­Bøw«¥sÐ�ªÃ�­¯¨@©0¡£«�©;¤�n©ÿÅ� Æ ¢?¡�¢�È�¨(¡�¢�¿�Ã Æ ¢[¤¦¢ÕÃW¾b¨ Å ¨@©M¿ t@«�¡½�[ã­¯¨@©;¤¡£¢Zª�¡£¢[¤�¢?©�í¯©�È�¢?¡£­®¨(¡1z�¢[¤�­Gt@©xª;¨@­¯©�ý¤�¿ Å ¨(©�㡽�[¡]½çÃ�¨wÃ Æ ¢ªz�­Ð¤�ªysÐ��½�¢�zRª¸¢]¡¦È�¨(¡�ø$�ª© Å ¢Døç¢?Ã�¡£­ Å §@��s®«�¢[¤�n

�r­Gt@«�¡£¢¥¤z¨Mn®À�o �[©az�¨Mn¯ÀZ��¤ Æ ¨�¾ Ã Æ ¢�øç¢[�ª© ¡£¢[¤�ª¸¨@©;¤¦¢ñÃ�­Gøç¢[¤î�ª©azãøç¢[�[© ©&¨(©�ê Å ¨@øŪ�«�ã¢�ã­Gøî¢[¤È�¨(¡�¹W¾�_�b�Ç»��+� Å ¨(©M¿åt(«�¡Ï�ªÃ£­®¨(©;¤R¾�­¯Ã Æ  U¡£¢[¤�¢?¢����ª©azß�â«¥sGs Å ¨Eø¼ø$�ª©IzÊÄ�«�¢?«�¢]­¯©yt&¿�¡�¢[¤Wª;¢ Å Ã�­G§�¢�sB½n���¨@¡Ã Æ ¢<ë��aÚ¬ê ® �(¤¦¢µzð��sGt(¨@¡£­®Ã Æ ø$¤�¿~øÝ��À�­Gø<«yø Å ¨@ø¼ø$�[©az�Ä6«&¢?«�¢�s¯¢]©yt(Ã Æ ¤¬¨ªÈÕÀZ�@�#�[©az�­¯©M¿;©&­¯Ã�½�ª�¡£¨�z�« Å ¢¤Ws®­Gt Æ Ã�sG½�s¯¨�¾¢?¡ « s¯¢[¤�¤ãÃ Æ �[©8À�ݳ¬[ø碥�ª©�©�¨@©�ê Å ¨@ø¼ª&«�ã¢$ã­Bøç¢[¤�n���¨(¡<Ã Æ ¢ �  H�a�rê ® �@¤¦¢�z ��sGt@¨(¡�­¯Ã Æ ø$¤�¿Ã Æ ¢ Å ¨(©8§�¢?¡Ï¤¦¢ç­Ä¤Rã¡�«�¢È Å ¨(©8¿ t(«�¡Ï�ªÃ�­¯¨(©â¤É¾�­®Ã Æ �zø$��À�­Gø0«¥ø Ä�«�¢?«�¢¼s®¢?©yt@Ã Æ ¨[È0ÀZ¨ Æ ��§�¢$�zø$�ª¡�t(­®©;��sª;¢?¡¦È�¨@¡]ø$�[© Å ¢v�7zM§@�ª©�ý��t(¢0¨�§�¢?¡Ã Æ ¨�¤�¢,¾�­®Ã Æ s¯¨@©yt(¢?¡�Ä�«�¢?«�¢Ds®¢?©yt@Ã Æ ¤�n>� Æ ­Ä¤çøÝ�ªÃ Å½Æ ¢[¤UÃ Æ ¢ ® ¢ Æ ��§�­®¨(¡�¨ªÈÃ Æ ¢�¡@êɫ⤦¢?¡[|bÛ@}��Üö»'}T¾b¨(¡��Ms®¨��9zÌ¿qz�­Ä¤ Å «â¤£¤¦¢µzé� ® ¨�§�¢¦n· ������� ³[±�¸ ���� û�é±�¸ ��üÏý � ¸?´�þ������r´�þXj���± � ²�����² � ³ª±���� � ¸

��¨(¡çÀ�êɫ⤦¢?¡<�[©az��ªê�«;¤�¢?¡³|bÛE}£��Ü�»�}x¾b¨(¡]�8s¯¨è�9z�¤�¿W��sBs���sBt(¨@¡£­¯Ã Æ ø ® «�ÃT�å§�� � ª�¡£¨�§�­'z�¢<¢�Ä�«�­G§@��s¯¢?©�ê;¢?¡¦È�¨@¡]ø$�[© Å ¢n���¨@¡çÃ Æ ¢��[êɫ⤦¢?¡$ã¡Ï� Å ¢¥¤�¿�¤ ÅÇÆ ¢�z�«ys®­¯©yt�¾�­¯Ã Æ �å§�� � z�¢�t(¡Ï�9z�¢[¤¼ø碥�ª©ø©&¨(©�ê Å ¨@øŪ�«�ã¢Ã£­Bøç¢[¤ ® ½w«yªcã¨R�ݼnH��¨(¡�Ã Æ ¢[¡(ê�«;¤¦¢]¡�㡽� Å ¢[¤�¿�§Wê�ë5�[���ô¤ Æ ¨�¾�¤��<¤Ws®­Gt Æ Ã « À�Ýô¨@¡_s®¢[¤£¤+¬=ª;¢?¡�È�¨(¡]øÝ�ª© Å ¢�9z8§(�[©�ÃÏ��t@¢ç¨�§�¢?¡�Ã Æ ¢w¨@Ã Æ ¢?¡lë��aÚ¬ê ® �@¤¦¢�zà��sBt(¨(¡�­¯Ã Æ ø$¤��[©azðÃ Æ ¢ �  H�a�rê ® �@¤¦¢�z���sGt@¨(¡£­®Ã Æ øݤ/n���¨(¡vÃ Æ ¢�ªê�«;¤�¢?¡Uã¡Ï� Å ¢¥¤�¿ �y� �a�zª�¡£¨�§�­'z�¢[¤jÃ Æ ¢�s¯¨�¾¢[¤�Ã5øî¢[�ª©l©�¨(©�ê Å ¨Eø¼ª�«�Ã�¢Ã£­Bøç¢b��øç¨@©yt�Ã Æ ¢�ë��aÚ¬ê ® �@¤¦¢�z0��sGt(¨@ê¡£­®Ã Æ øݤ�¿�¢Z§�¢?©çÃ Æ ¨(«yt Æ §Wê�ë5�[��� Æ �(¤�Ã Æ ¢[s¯¨�¾b¢[¤¦Ãaø碥�ª©ç¡�¢[¤Wª;¨(©â¤¦¢0ã­Bøç¢n9�â¨@¡�|~Û@}£��Ü�»�}�¿�§Wêáë5�[�����ª¥ª;�ª¡�¢?©�Ã�sG½0­Bø¼ª�¡£¨�§�¢[¤jÃ Æ ¢Yª;¢?¡¦È�¨@¡]ø$�[© Å ¢�¨ªÈXs¯¨�¾ßª�¡£­®¨(¡£­®Ã�½0¡£¢�Ä�«�¢[¤�ý¤W�ªÃbÃ Æ ¢�¢ZÀMª;¢?©;¤�¢¬¨[È Æ ­Gt Æ ª�¡�­¯¨(¡�­¯Ã�½¡£¢#Ä6«�¢¥¤¦Ã½¤�n[��¨(¡�Ã Æ ¢�¹W¾�_�b�½»]�+�a¾¨@¡]�8s¯¨è�9z�¿���sGsW��sGt@¨(¡£­®Ã Æ øݤ ® «&Ã[�å§�� � ª�¡�¨�§�­'z�¢ã¡£¨@«yt Æ sG½�¢�Ä�«�­G§@��s¯¢?©�ê;¢?¡¦È�¨@¡]ø$�[© Å ¢n

· ������� ³[±�¸ ��� ¹<±����������j´�þ5j��ɱ � ² � �����j´z» � ¸���r� ® s¯¢�¨Mn3��ª�¡�¢[¤¦¢]©�ÃϤU��ªyª¥s¯­ Å �ªÃ£­®¨(©�êá¤Wª;¢ Å ­p¿ Å ª;¢?¡¦È�¨@¡]ø$�[© Å ¢1z��[ý�öÈ�¨@¡[²£¡£¢¥�(¤¦¨@©;� ® s¯¢�µ Æ ¨è¤¦Ã�ê ® �@¤¦¢�zî�ª©azz�­Ä¤W��ê ® �@¤¦¢�z Å ¢?©�Ã�¡½��s¯­G¶]¢�zç¤ Å½Æ ¢�z�«ys¯­®©ytw¨[ÈY|bÛ@}£��Ü�»�}<�ª©az�¹W¾�_�b�½»]�+��nY��¨(¡Ds®­Gt Æ ÃY¾¨(¡��Ms®¨��7z�¤ « ­1n ¢n®¿�Ã Æ ¢

À�ê�«;¤�¢?¡<�ª©az��ªê�«;¤¦¢?¡¼|~Û@}£��Ü�»�}éÃ�¡½� Å ¢[¤'¬Ï¿vz�­Ð¤���ê ® �@¤¦¢�z�¤ ÅÇÆ ¢�z�«ys®­¯©yt Æ �@¤0�#¤Ws®­Gt Æ Ãº�9zM§@�ª©�ý��t(¢nËr�¤RÃ Æ ¢¾¨@¡]�8s¯¨è�9zð­®©�Ã�¢?©;¤¦­®Ã�½é­®© Å ¡�¢[�(¤�¢[¤�¿�«;¤�­¯©yt Æ ¨è¤¦Ã£ê ® �@¤¦¢�zñ¤ Å½Æ ¢�z�«ys¯­®©ytç­GøŪ�¡£¨�§�¢[¤�Ã Æ ¢î��ª¥ªys¯­ Å �ªÃ�­¯¨(©&ê�¤�ª¸¢ Å ­p¿ Ū;¢?¡¦È�¨@¡]ø$�[© Å ¢Døî¢?ã¡�­ Å ¤ ® ½$��ªyª&¡£¨�À�­Bø$�ªÃ�¢�sG½Å�£ÝÅn�§W¨@ø¼ª;�[¡£­®©yt0ý� ® s¯¢[¤a¨8n��@�w�[©azz¨8n�� ® ¿¸Ã Æ ¢l�9zM§@�ª©�ý��t(¢¨ªÈ Æ ¨�¤�Ã£ê ® �(¤�¢�z÷¤ Å½Æ ¢�z�«ys®­¯©yt�s¯¢[¤�¤¦¢?©;¤î�(¤çÃ Æ ¢ Å ¨@ø¼ªys®¢�À�­¯Ã�½ð¨[ÈlÃ Æ ¢ðz�­Ä¤W� Å ¨(©�ã¡�¨@sGs®¢?¡<­¯© Å ¡�¢[�(¤�¢[¤ « È�¡£¨@ø U¡£¢[¤�¢?¢��<ã¨Å��«ysGs Å ¨@ø¼øÝ�ª©azRÄ6«&¢?«�¢?­®©ytM¬´n

�]V�)� ="�70�#�� �(�(����E�+*ÊCY��2� �$(0���/"�(� ?!� ��?.��0����4�%'(X(����/� %'(�����7� �%/��)� �(H%>(��1%'�� H*�)� �7� H�0)� �70 �%+70 H���aCY�/7� 5 �\� ����0(X�����)� 9�071%/�? =6B�/7X%>"�7����? �(0(X�0)E%+����(��1%/�?����\/ �Æ%'����)� ` ��E2_�+6y��)� H�071%/�? ��

Page 133: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À��E�

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

« �£¬Æ÷#¢[�[©z��¢[¤�ª¸¨@©;¤¦¢T�­Gøç¢

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

! CQ = 16CQ = 128CQ = Infinity

«�® ¬�÷#¢[�[©zÚ�¨(©�ê�§W¨@ø¼ª&«�ã¢��­Gøî¢

°�±É² jj³[´zk�µÉ¶ylÌ·ç¹W¾�_�b�½»]�+�� ��Å½Æ ¢�z�«ys®­¯©yt�r_sBt(¨(¡�­¯Ã Æ ø  r¢?¡¦È�¨@¡]ø$�[© Å ¢çÈ�¨(¡Ou¬­Ä¤W�&¤³¾�­¯Ã Æ  U¡£¢[¤�¢?¢��§W¨Eø¼ø$�[©azxw�«�¢?«�¢]­¯©yt

Page 134: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À���À

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

« �£¬Æ÷#¢[�[©z��¢[¤�ª¸¨@©;¤¦¢T�­Gøç¢

FCFS C-LOOKï LOOKï SSTFð VSCAN(0.2) SPTF ASPTF(6)SPCTFô ASPCTF(6)ôScheduling Algorithmõ

0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

! CQ = 16CQ = 128CQ = Infinity

«�® ¬�÷#¢[�[©zÚ�¨(©�ê�§W¨@ø¼ª&«�ã¢��­Gøî¢

°�±É² jj³[´zk�µÉ¶8{�·ç¹W¾�_�b�½»]�+�� ��Å½Æ ¢�z�«¥s¯­¯©¥t�r_sBt(¨(¡�­¯Ã Æ øf r¢?¡�È�¨(¡�ø$�ª© Å ¢�È�¨@¡Du¬­Ä¤W�&¤ç¾�­®Ã Æ ��«ysGsj§W¨@øçêøÝ�ª©azzw�«�¢?«�¢]­¯©yt

Page 135: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À��E�

�¬¨è¤¦Ã£ê1���(¤�¢�z « ��sGsHn4§H��n �y� �D¬ u�­Ð¤W��ê1���(¤¦¢µz§Wêáë5����� �  §��a� §Wêáë5�[�D� �  §��a�

�Ò¡Ï� Å ¢ §awÁ��� §awÁ�2À §aw��ôÀ��E� §aw��2ÀZ�@�� ½�© �#"�¢?© « À�¬ �@�EqMn3�@¢ �@�EqMn¯ÀZ¢ Ê;Ê;Ú̵G��Ê Ê;Ê¥ �µGk �� ½�© �#"�¢?© « �¬ ¡�E�Mn3��À ¡�E¨Mn¯À@À   ¤ ¤�µËÊ¥¤   ¤ ��µG� {� ½�© �#"�¢?© « ¡8¬ ¤ ¤  ÒµB� { �@�E¢Mn��o �E�@qMn®À�� ¤ ¤ {�µG��Ú� ½�© �#"�¢?© « �¬ ¤ { �ÒµB� � ¤�l~l̵Al¥  �E�@�Mn3��¡ �E�@q8n�¨@q§W¨@ø¼ª�¡�¢[¤£¤ ¶8��¶¸µB{�Ê ¶8�Ò¶;µB{ k ÀZ¢�¡yn^o�¡ ÀZ¢�¡¥npo�¨

« �¬� U¡£¢¥¤¦¢?¢��$§W¨@øÅø$�ª©az�w¬«&¢?«�¢?­®©yt

�¬¨è¤¦Ã£ê1���(¤�¢�z « ��sBsHn4§H��n �¥� � ¬ u¬­Ä¤W��ê?���@¤¦¢�z « ��sGsHn �y� ��n �y� �D¬§Wêáë5����� �  §��a� §Wêáë5�[�D� �  §��a�

�Ò¡Ï� Å ¢ §awÁ�Á� §aw���À §awÁ�ôÀ��E� §aw��2ÀZ�@�� ½�© �#"�¢?© « À�¬ �@�EqMn3�@� �E�@q8n¯À�¢ Ê;Ê¥ �µG��Ú Ê;Ê¥ �µËÚ¥k� ½�© �#"�¢?© « �¬   ¤�Ê�µB �Ê ¡¦�@¨8n¯À(À ¡¦�@�Mn3�@q   ¤ ��µG�  � ½�© �#"�¢?© « ¡8¬ �@�E¨Mn3�@� �E�@¢8n��£o ¤ ¤  �µËÚ l ¤ ¤ k�µG��l� ½�© �#"�¢?© « �¬ ¤�l l�µB��¶ ¤�l l̵ml¥  �E��¡yn3¨@� �E�@�8n��@�§W¨Eø¼ª�¡£¢¥¤£¤ ¶8� �ÒµB��Ú ÀZ¢�ÀEn��@¨ ÀZ¢@�Mn3¢@q ¶8� ��µG� �

«�® ¬���«ysGsU§W¨Eø¼ø$�ª©Iz�w�«�¢?«&¢?­¯©yt

¯ � °���´zk�µËÊÌ·[÷#¢[�[©¼Ú�¨(©�ê�§W¨@ø¼ª&«�ã¢[�­Bøç¢[¤ « ø$¤'¬j¨@¡ar_ªyª¥s¯­ Å �ªÃ£­®¨(©Å��«&©��­Gø碥¤ « ¤¦¢ Å ¬ÒÈ�¨@¡,²´��¢[�[ê¤�¨(©;� ® s¯¢�µç§W¢?©�ã¡Ï��s¯­B¶?¢�z ��Å½Æ ¢�z�«ys®¢?¡½¤

Page 136: Aggressive Centralized and Distributed Scheduling ofDisk Requests

À��E�

$YÌ&%>Ì(' Ñ_ÏDÖ Ö Ø`×8Ó*),+.-/)10YÙ�Ð]ÏYÔ32 )�0YÔ��¨(¡»z�­Ð¤���ê ® �(¤�¢�z Å ¢?©�ã¡Ï��s®­G¶?¢�zî¤ Å½Æ ¢�z�«ys®­¯©yt0«â¤¦­¯©¥tç¨(©ysB½ Æ �ª¡ÙzM¾��[¡£¢?êá¤Wª;¢ Å ­^¿ Å ��©�¨�¾as¯¢µzMt(¢�¿�§Wêáë5�[���

t(¢]©�¢?¡½��sGsB½Dª�¡£¨�§�­'z�¢¥¤ÒÃ Æ ¢>s®¨�¾b¢[¤¦ÃXøç¢[�[©v¡£¢[¤�ª¸¨@©;¤¦¢�Ã�­Gø碥¤���øç¨@©yt¬Ã Æ ¢�¤�¢?¢���êÉ¡�¢�z�« Å ­¯©ytÕ��sBt(¨(¡�­¯Ã Æ ø$¤/nX��«ysBs¯ê��©�¨�¾as¯¢�zMt@¢�¤ Å½Æ ¢�z�«¥s¯­¯©¥tv��sBt(¨(¡�­¯Ã Æ ø$¤�¿è¤¦« Å½Æ �(¤ �  §��a�¿ª�¡�¨�§�­'z�¢�Ã Æ ¢ Æ ­Bt Æ ¢¥¤¦ÃHs¯¢�§�¢ZsФ�¨ªÈ�ª;¢?¡�È�¨(¡�ø$�ª© Å ¢n��©�ê ® ¨è�ª¡Ùz Å � Å½Æ ¢[¤l�ª©azäª�¡£¢�È�¢]Ã Å½Æ ­¯©ytõ��sBt(¨(¡�­¯Ã Æ ø$¤0¤ Æ ¨(«ysÄz ® ¢c¢�À���øç­¯©&¢�z ® ¢�È�¨@¡£¢$«;¤�­¯©yt �  §��a�N¨@¡r �  §��a� « ¨£¬Ï¿��(¤ Å � Å½Æ ¢?êᤦ¢?©;¤�­¯Ã�­G§�­¯Ã�½ªz�¢�t(¡Ï�9z�¢¥¤ �  H�a�rê ® �(¤¦¢µzé��sGt@¨(¡£­®Ã Æ ø ª;¢?¡¦È�¨@¡]ø$�[© Å ¢�È�¨(¡ß¤¦¨@ø¨@©�ê® ¨��[¡wz Å � ÅÇÆ ¢ Å ¨(©M¿åt(«�¡Ï�ªÃ£­®¨(©;¤�nYû ©�ª;�[¡£Ã�­ Å «ysÄ�ª¡]¿;�ª«�Ã�¨@ø$�[ã­ Å ª�¡£¢�È�¢]Ã Å½Æ ­¯©yt0¨@©éÈ�«ysBs�¡�¢[�9z Æ ­¯ÃϤ Å �ª© Å �ª«;¤�¢¢�À Å ¢[¤�¤¦­G§�¢Õ� Šã«;�[ã¨(¡Yøç¨@ã­¯¨@©c�(¤>¾¢ZsGs��@¤çs®¨�¾¢?¡�¨@©�ê ® ¨è�ª¡wz Å � Å½Æ ¢ Æ ­®Ã�¡½�ªÃ�¢[¤/n

� ¢�Ä�«�¢?©�ã­Ä��sW¤ ÅÇÆ ¢µz�«ys¯­®©ytç¨[È�¡£¢¥�9zð¡�¢�Ä6«&¢[¤¦ÃϤ¬­Gø¼ª&¡£¨�§�¢[¤�Ã Æ ¢Rª;¢?¡¦È�¨@¡]ø$�[© Å ¢0¨ªÈ÷z�­Ð¤���ê ® �@¤¦¢�z Å ¢?©�Ã�¡½��s¯ê­G¶]¢�zw¤ ÅÇÆ ¢�z�«ys®¢?¡½¤rÈ�¨(¡ß¤¦¨Eøç¢a¾¨@¡]�8s¯¨��7z�¤ « ¤�« Å½Æ �@¤Ã Æ ¢[|b}�ͪÎ�»bã¡Ï� Å ¢@¬´n � ¢#Ä6«�¢]©�Ã�­Ð��s̤ ÅÇÆ ¢µz�«ys¯­®©yt�¨[È=¾�¡�­¯Ã£¢¡£¢#Ä6«�¢¥¤¦Ã½¤�ª�¡�¨�§�­'z�¢[¤U�_ø$�[¡]t@­¯©;��sª¸¢]¡¦È�¨(¡�ø$�ª© Å ¢­Bø¼ª�¡£¨�§�¢�ø<¢?©�Ã;­4Èb¾�¡£­®Ã£¢>ª&¡£¢ ® «8v�¢]¡£­¯©¥t�­Ð¤�¢?©;� ® s¯¢�zbn`��Ã Æ ê¢?¡�¾�­Ð¤¦¢è¿�­¯Ã1z�¢�t(¡Ï�9z�¢[¤aª;¢?¡¦È�¨@¡]ø$�[© Å ¢ ® ½ç­®© Å ¡£¢¥�(¤¦­®©yt,øî¢[�ª©$¡£¨@ý�[ã­¯¨@©;��s�sÄ�ªÃ�¢?© Å ­®¢[¤/n

u¬­Ð¤���¤X¾�­¯Ã Æ øÝ��À�­Gø0«yø Å ¨@øÅø$�ª©az�Ä6«�¢]«�¢>s®¢?©yt(Ã Æ ¤r¨[ÈUÀZ�@��¨ªÈ�Ã�¢?©�ª�¡�¨�§�­'z�¢>ª;¢?¡¦È�¨@¡]ø$�[© Å ¢b©�¢[�ª¡íÃ Æ �[èªÈ÷z�­Ð¤���¤Y¾�­¯Ã Æ «&© ® ¨(«&©az�¢�z Å ¨@øÅø$�ª©az�Ä�«�¢?«�¢¥¤/n�û ©à¤�¨@øç¢ Å �(¤�¢[¤�¿j�³¿;©�­®Ã£¢ Å ¨@ø¼øÝ�ª©azOÄ6«�¢]«�¢,s®¢?©yt(à ÆÆ ¢�sBª;¤Ã£¨<¡£¢µz�« Å ¢�Ã Æ ¢l¤¦ÃÏ�ª¡]§@�[ã­¯¨@©#¨[È Æ ­Gt Æ ª�¡£­®¨(¡£­®Ã�½w¡�¢�Ä6«&¢[¤¦ÃϤ/n

u¬­Ð¤���ê ® �@¤¦¢�z Å ¢?©�㡽��s¯­B¶?¢�z�¤ ÅÇÆ ¢µz�«ys¯­®©yt�­Ð¤0��¡£¢¥�(¤¦¨@©;� ® s¯¢���s¯Ã�¢?¡£©;�[ã­B§�¢çã¨àã¡Ï�9z�­®Ã£­¯¨@©;��s Æ ¨è¤¦Ã£ê ® �@¤¦¢�z¤ Å½Æ ¢�z�«ys¯­®©ytyn9�â¨@¡b¤¦¢�§�¢?¡Ï��s;¨ªÈjÃ Æ ¢�uDç �ª©az��� ðÃ�¡½� Å ¢[¤W�ª©az$¤�¨@øç¢�¨[ÈH|bÛ@}£��Ü�»�}v㡽� Å ¢[¤=¾�­¯Ã Æ ¡ã«â¤¦¢?¡Ï¤¨(¡�s¯¢[¤�¤�¿�z�­Ð¤���ê ® �(¤�¢�z�¤ ÅÇÆ ¢µz�«ys¯¢]¡½¤¬¨@«�Ã]ª;¢?¡�È�¨(¡]ø Æ ¨�¤�Ã£ê ® �(¤�¢�zñ¤ Å½Æ ¢�z�«ys®¢?¡½¤�¨ªÈ Å ¨Eø¼ª;�ª¡Ï� ® s®¢ Å ¨@ø¼ªys®¢�À�­¯Ã�½@n� Æ ¢Oª¸¢]¡¦È�¨(¡�ø$�ª© Å ¢c�9zM§@�ª©�ý��t(¢�¨[Ȫz�­Ð¤���ê ® �@¤¦¢�z ¤ Å½Æ ¢�z�«ys®­¯©yt�­®© Å ¡�¢[�(¤�¢[¤É¾�­®Ã Æ Ã Æ ¢c��øî¨(«�©�Ãw¨[Èv­¯©�ã¢]¡£ê¡£¢#Ä6«�¢¥¤¦Ã Å ¨@© Å «�¡�¡£¢?© Å ½ç��§@�ª­BsÐ� ® s¯¢v�[ì¢[� ÅÇÆ z�­Ä¤W�bn46587 9;:=<?>[email protected]?G HID�JK< L�F?MONQP,R STJKDUNVF W;PXNVR Y1Z*[/NA\�>A] S^F.@

Y=_`>ACUNTHa]

�,b3c�d.d eEfhg&cjilkme�À3n�ø�cjkoeEdVgpboeqi�§Oe r8n�sGssdW½odtg&e�ø ª�e r uvilr�ø6nwk�f�eqe/vxeEfhgydziwu{n}|3|~c�kyt�dW½odtg&e�ø���sje�§Oe�s��k3i�¾asjeE|Mt}eVg&i.|~c�dW��� ® nldte�|qfhe k�gpryn�sjcB¶ eE|.d&f�b3e�|~�ysjc�kytyn¼��boe k�dpf8b3eE|��ysjc�kyt6gpb3e{|~c�d��.rpe�ÄO�3eEd g�g&r8nlf�eEdh�gpboeDs�n}f'��iwu�dW½odtg&e�ø���sje�§Oe�s�cjk�uvilr]ø�nwgpc�ilkRª3rpeZ§Oe k~gyd�gpb3eT��d e�iwu�n�sBtlilr&cjg&byø6dKg&b�nwg�iEª3gpcBø�cG¶Ue,uvilr�d�½3d gpe�øª�e rtuvi}r]ø6nEk�fheRø�e g&rpc�fUd/nO�#i�¾,e�§Oe rU��n.dpf8b3eE|~�ys�e rsf nwk�dtgpcBsGs=nwg&gpe�øŪ3g�g&izª3r&e�§Oe k�gAg&b3e6d g8nwr�§}nwgpc�ilk�iwub3cBtlb3��ª3rpc�ilr&cjg�½.rpe�ÄO�3eEd g8d ® ½±ø�cjk3cBø�cG¶�cjk¥tVg&b3eVr&e�ÄO�3eEdtgTr&eEdWª�ilk�dte6gpcBø�e,§}nwr&c�nEk�fhenO�3ilr�eZÀMª�e r&cGø�e k�g8d��d cjkyt6gpboe^uv�ysBsXdW½odtg&e�ø*gprynlfhe�dh��gpb3e�b3i�dtg,ø{i�|~e�sXª�nld&dteEdsn;dtcBø¼ªys�eAboc���s�i�ª3rpc�ilrpc�g�½xýxn�t;gpi?gpb3e�|�c�dW�dt� ® dW½odtg&e�ø�ø�i�|�e�s3n�sji}kyt[¾�cjgpbQe�nlf8bQrpe�ÄO�3eEd g�n=�,boc�d�n�sGsji�¾�d�nT|~c�dW��� ® nldte�|Qdpf8b3eE|~�ys�e r�gpi[tlcB§Oe>ª3r&cjilr&cjg�½gpi�gpcBø�e ��fhrpc�gpc�f n�s�nwk�|6gpcBø�e ��sjcGø�cjg eE|Qrpe#Ä��3e�dtg8d�n

$YÌ?ÍYÌ&% ��2�Ô3���ÂÕ��_ÏYÕ5Ô����R×yØHÙ�Õ5Ô� eEfhg&cji}k¼¨8nj�@n���d b3i�¾�dKgpb�nwg,g&b3e�r ��  �a� « ¨¬XnEk�|¼r �� ,¡ �a� « ¨£¬�n�sGt}ilr&cjgpb¥ø6d�b�n�§OeYø�eEnwkQr&eEdWª�i}k�dte

gpcBø�eEd�e�ÄO�3cG§}n�sje k�g « ¾�cjgpbocjk�n;uve�¾�ª�e r8f�e k~g�¬Tgpi ��  �a�¢nwk�| �� ,¡ �a�,��r&eEdWª�eEfhg&cG§Oe�sB½n±�,b3c�dQdteEf�gpcji}k|~e�ø{ilk�d gpr8nEgpeEd,g&b�nwg�gpb3e£n�tleU�(d e k�dtc�gpcB§Oe ��  �a��n�sBtlilr&cjg&byø6d>ª3r&i�§�c�|�e�ø���f8b ® e gpg&e r�dtg8nEr]§}nwg&cji}k.rpeEd c�dt�g8nEk�fheO��¾�b3c�f�b�sje�nl|3d�gpi?gpb3e{fhi}k�f/sj��dtcji}k¤g&b�nwgsn}|3|~cjk¥t.n�t}e ��dte k�d cjg&cG§�cjg�½;g&i.|~c�dW��� ® n}dteE| ��  �a��n�sGtli}�rpc�gpbyø�d,c�d_t}e k3e ryn�sGsB½?nl|M§�c�d&n ® s�en[�3�3rpg&b3e r]ø{ilrpe��¥n�tle ��dte k�dtcjg&cG§Oe ��  �a��n�sGt}ilr&cjgpb¥ø6d1��dt��n�sGsG½Oª3rpi�§�c�|~e® e gpg&e r�dtgynwr�§lnEgpc�ilk;r&eEdtc�dtgynwk�fheTg&b�nwk§¦�¨aÚ#� ® nldte�|zn�sGt}ilrpc�gpbyø�d/n

��cGt}�3rpe�d`¨8nj�Z¢#Þ8¨8n���¡�ª3rpeEd e k�gKg&b3e�d]ÄO��nwr&eE|Vf�iOeh©6f�cje k�g8d�iEuX§}nwrpc�nwg&cjilk{fhi}rprpe�dWª�ilk�|�cjkytQg&iAg&b3eYø�eEnwkrpe�dWª�ilk�d e�g&cGø�eEdHtlcB§Oe k6cjk¼¿ tl�orpeEdY¨Mn��'Þ8¨8n�¨8nar�d,e�À8ª�eEfhgpe�|¥� ¡ �(¦5�[����ª3r&i�§�c�|�eEd,gpb3e ® eEd g�d g8nwr�§}nwgpc�ilk

Page 137: Aggressive Centralized and Distributed Scheduling ofDisk Requests

����¡

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

5

10

15

20

25

30

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

« n¬   rpe�dte e�� ¡ i@øÅø6nwk�|�w#�oe �3e c�kyt

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

5

10

15

20

25

30

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

«�® ¬��3�ysGs ¡ iEø¼ø6nwk�|�w��3e �oe cjkyt

°�±�² j�³w´Ok�µ�¶8��·Q¸,¹8º�º¼»l���Enpo#qw½Q¾ � e#Ä��3eUk~g&c�n�s � f8b3eE|~�ys�cjkytTr_sGt}ilr&cjgpb¥ø   e r uvilr]ø�nwk�fhe

Page 138: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���Eq

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

10

20

30

40

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

« n¬   rpe�dte e�� ¡ i@øÅø6nwk�|�w#�oe �3e c�kyt

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

10

20

30

40

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

«�® ¬��3�ysGs ¡ iEø¼ø6nwk�|�w��3e �oe cjkyt

°�±v² j�³E´Ok¿µ�À¥��·ç|b}oÁwÂO¹8���En��@qE½Q¾ � e�ÄO�3e k�gpc�n�s � f�boeE|~�ys�cjkytTr_sGt}ilrpc�gpbyø   e r uvilr�ø6nwk�f�e

Page 139: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���E¨

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

10

20

30

40

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

« n¬   rpe�dte e�� ¡ i@øÅø6nwk�|�w#�oe �3e c�kyt

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

10

20

30

40

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

«�® ¬��3�ysGs ¡ iEø¼ø6nwk�|�w��3e �oe cjkyt

°�±v²~j�³E´zk�µ�À¥¶�·#Ã�ÄA�8Å0�Y�UÆh� �Mn3qw½Q¾ � e�ÄO�3e k�gpc�n�s � f�b3e�|~�ysjc�kyt�rYsGtli}rpc�gpbyø   e rtuvi}r]ø6nEk�fhe

Page 140: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���o

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

20

40

60

80

100

120

140

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

Sat

urat

edS

atur

ated

Sat

urat

ed¯

« n¬   rpe�dte e�� ¡ i@øÅø6nwk�|�w#�oe �3e c�kyt

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

20

40

60

80

100

120

140

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

Sat

urat

ed

«�® ¬��3�ysGs ¡ iEø¼ø6nwk�|�w��3e �oe cjkyt

°�±�² j�³w´Ok�µ�À�Àx·_|xÇ ÄjÅUÈ�|����8n�qE½Q¾ � e�ÄO�3e k�gpc�n�s � f8b3eE|~�ys�cjkytRrYsGtli}rpc�gpbyø   e r uvilr]ø�nwk�fhe

Page 141: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���E�

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

2

4

6

8

10

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

Sat

urat

edS

atur

ated

Sat

urat

ed¯

« n¬   rpe�dte e�� ¡ i@øÅø6nwk�|�w#�oe �3e c�kyt

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

20

40

60

80

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

«�® ¬��3�ysGs ¡ iEø¼ø6nwk�|�w��3e �oe cjkyt

°�±�² j�³w´Ok�µ�À¥¤�·QÉa�&Ê~¹����x�@n3�w½Q¾ � e#Ä��3eUk~g&c�n�s � f8b3eE|~�ys�cjkytTr_sGt}ilr&cjgpb¥ø   eUrtuvilr�ø6nwk�fhe

Page 142: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���E¢

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

2

4

6

8

10

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

ed¯

Sat

urat

ed

Sat

urat

ed¯

Sat

urat

edS

atur

ated

Sat

urat

ed¯

Sat

urat

edS

atur

ated¯

Sat

urat

edS

atur

ated

Sat

urat

ed¯

« n¬   rpe�dte e�� ¡ i@øÅø6nwk�|�w#�oe �3e c�kyt

C-LOOKª LOOKª SSTF« VSCAN(0.2) SPTF ASPTF(6) SPCTF¬ ASPCTF(6)¬Scheduling Algorithm­

0

2

4

6

8

10

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

® No Opt.SSR.SSW.SSR

Sat

urat

ed¯

Sat

urat

edS

atur

ated

Sat

urat

edS

atur

ated

Sat

urat

ed¯

«�® ¬��3�ysGs ¡ iEø¼ø6nwk�|�w��3e �oe cjkyt

°�±�² j�³E´zk�µ�À¥ �·_��¹?�o»��Ëv�¥�En��w½£¾ � e�ÄO�3e k�gpc�n�s � f�boeE|~�ys�cjkytTr_sGt}ilrpc�gpbyø   e rtuvi}r]ø6nEk�fhe

Page 143: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���E�

rpe�dtc�d g8nEk�fhe�uvilr�gpb3e?¦�¨aÚ#� ® n}dteE|�n�sGt}ilr&cjgpb¥ø6d/nä�,b3e§n�t}e �(d e k�d cjgpcB§Oe ��  �a�Ìn�sGt}ilrpc�gpbyø�d�b�n�§Oexs�i�¾,e rd]ÄO��nErpeE|?fhiOeh©�fhcje k�g8dXiwuH§}nErpc�nEgpc�ilk;g&b�nwk ¡ �(¦5�[���Íuvilr�gpb3e[ø6nwÎ i}rpc�gW½�iwu�gpb3es|~c�dW��� ® n}dteE|?dpf8b3eE|~�¥sje rcGøŪysje�ø�e k�g8nEgpc¼ilk�d�n>�3i}rD�3�ysBs�fhi@ø¼ø�nwk�|¼ÄO�3e �oe cjkytQcBø¼ªys�e�øVeUk~gynwgpc�ilk�d�iEu#Ã�ÄA�8Å0�Y�UÆ#nEk�|Ò|xÇUÄjÅ È�|��¥g&b3ed]ÄO��nErpeE|?fhiOeh©�fhcje k�g8dXiwuH§}nErpc�nEgpc�ilkzuvi}r�gpboe�n�tle ��dteUk�dtc�gpcG§Oe ��  �a��n�sGt}ilr&cjgpb¥ø6d�nwr&e,sje�dpd,gpb�nwk�q@�ÝÏiwugpboe.fhi}rprpe�dWª�ilk�|�cjkytä§}n�s��3eEd�uvilr ¡ ��¦5�[�D��naû(k�n�sGs�f n}dteEd��_r ��  �a� « ¨¬�nwk�|Âr �� ,¡ �a� « ¨¬�ª3rpi�§�c�|~e® e gpg&e r�dtgynwr�§lnEgpc�ilk�rpeEd c�d g8nwk�fhe6gpb�nEk ��  �a�¢nEk�|âr �� Ð¡ �a�=��rpe�dWª�eEfhg&cG§Oe�sB½n±�3ilrQg&b3ez|b}3ÁwÂ�¹Qgpr8n}fheO�n�t}e ��dte k�d cjg&cG§�cjg�½�|�eEfhrpe�nldte�d,gpb3esd]ÄO��nErpeE|6fhiOeh©�fhc�e k~g=iwu9§}nwrpc�nwg&cjilk ® ½�nldaøV��f8b{nldDo�¨£ÝÅn

· ������� ³E±�¸ ��� ¹�±��EÑ��ÓÒwÑ�´�Ô5j���± � ² � ���EÑ�´z» � ¸����n ® sjeR¨8n���d b3i�¾�d�gpb3e�ø�eEnwk?rpeEd�ª�ilk�d eQgpcGø{eEd�nwk�|Õd]ÄO��nErpeE|.fhiOe�©6fhc�e k�g8d,iwu�§}nwr&c�nEgpcji}k;uvilr¼²&rpeEnE�

dti}k�n ® sje�µcBø¼ªysjeZøVe k�g8nEgpc�ilk�dViEu�b3iOd gp� ® nld eE|ÍnEk�|¢|~c�d��~� ® n}dteE|¢fhe k�gpryn�s�cG¶ eE|�d&f�boeE|~�ys�e r8d6��dtc�kytg&b3er �� ,¡ �a� « ¨£¬�n�sBtli}rpcjg&byø±n��,boe³ø�e�nwk;r&eEdWª�i}k�dte�g&cGø�e�d#|~c�dWªys�n�½OeE|;nErpeQuvilrsfhilk8¿ tl�3rynwg&cjilk�dAgpb�nwgQ|�ik3i}g,nE�3gpiEø6nwg&c�f n�sGsB½�ªorpehuve gyf�b£|3nwgyn�ilkQuv�ysGs3r&eEnl|Qb3c�g8d/n9�,b3e�g8n ® sje�|�iOeEdKk3i}g=fhilk�g8nEcjkRr ��  �a� « ¨£¬Xª�e rp�uvilr�ø6nwk�fhes|3nwgyn~�xdtcjk�fhe�r �� ,¡ �a� « ¨¬aª3r&i�§�c�|�eEd�dt�yª�e r&cji}r_ø�e�nwk6rpeEd�ª�ilk�d eQgpcGø{eEd�uvilrTfhi}kM¿ t}�3r8nEgpcji}k�d¾�cjg&b�ª3rpehuveUg8f8b3cjkytsilk6uv�ysGsxrpeEn}|zb3c�g8d�|~c�dpn ® sjeE|�n

�3ilr�gpb3esgW¾=i¼�   gpr8n}fheEd���|~c�d��~� ® nld eE|.dpf8b3eE|��ysjc�kytQilkysB½6rpeEd �ysjgyd1c�kxs�i�¾,e raø�e�nwk6rpeEd�ª�ilk�d eQgpcGø{eEduvilr��3�ysGs�f�i@ø¼ø6nEk�|¼ÄO�3e �3eUcjkyt�fhi}kM¿ t}�3r8nEgpcji}k�d/n��3ilr�gpb3e�uvil�or[uDà ¡ gprynlfhe�dh�x|~c�d��~� ® nld eE|;d&f�boeE|~�ys�cjkytc�d�d �yª�e rpc�ilr,uvi}r ® ilg&b   rpe�dte e��{nwk�|z�3�ysGsÓfhi@øÅø6nwk�|RÄO�3e �3e c�kytynH��n ® sje�¨Mn3� ® dtb3i�¾�d�gpb�nEg�|�c�dW��� ® nld eE|dpf8b3eE|��ysje rydÖuvi}r¼�3�ysBs�fhiEø¼ø6nwk�|ÊÄO�3e �3eUcjkytÕfhi}kM¿ t}�3r8nEgpcji}k�d³t}e k3e ryn�sGsB½¤b�n#§Oe{gpb3e ® e�dtg « i}rVr&il�yt}bysG½e�ÄO�3cG§}n�sje k�g/¬�d g8nEr]§}nwg&cjilk¢r&eEdtc�dtg8nEk�fhen �3ilr   r&eEdteUe���fhilk8¿ tl�3rynwg&cjilk�dh��uvil�3r?iwu�g&b3e�dtcBÀ¾,i}r]�8sjiOn}|3dnlf8b3c�e�§Oe_s�i�¾,e r�r&eEdWª�ilk�dte�g&cGø�eY§}nwr&c�nwk�fheEd>¾�cjg&b6b3iOd gp� ® nld eE|.dpf8b3eE|~�¥sjcjk¥tyn

$YÌ?ÍYÌ?Í ÎDÏYÐ�ÐÒÑ�ÓYÔ~�yÕ=Ö �R×yØHÙ�ÕXÔ�,b3e�eZÀMª�e r&cGø�e k�g8d�c�k;gpboc�d�dte�fhgpc�ilk.n}dpd �yø�eTgpb�nEg#e�nlf8bzr&e�ÄO�3eEdtg�nErpr&cG§�cjkyt{nwg�nV|�c�dW�6b�n}d#n�sjr&eEnl|M½

® e e käø6nEr]�OeE|¤bocGtlb�ilrRsji�¾ ª3rpc�ilrpc�g�½ « en©t¥nj� ® ½�nEk�n�ªyªysjc�f nwg&cji}k×i}rÉ¿åsje?dW½odtg&e�ø nwg�gpboezboiOdtg�¬+nßr|~c�dW��� ® n}dteE|6d&f�b3e�|~�ysjeUr,��d cjkyt�n��wØn�sGt}ilr&cjgpb¥øÙg&b3e k�tlcB§OeEd`ª3r&eEfheE|�e k�fhe�gpi�gpb3e�b3cGt}bxªorpcji}rpc�gW½ « g&cGø�eU�fhr&cjgpc�f n�sÚnwk�|;gpcGø{e �0s�cGø�cjg&e |~¬Xr&e�ÄO�3eEdtgyd/n ¡ i@ø¼ø{ilk�ª�e rpcBª3b3e ryn�s ® ��d ªorpilg&i�fhi@s�d « dt��f�bÕn}d �o¡a� û(�?�¬�|�ik3i}g�k3eEfheEd&dpnErpcGsB½�ª3rpi�§�c�|~e�uvilr>ª�nldpd cjkyt�gpboc�dKg�½8ª�e�iwu�fhilk�gpr&i@sxcjk~uvi}r]ø6nEgpcji}k�n=��i�¾=e�§Oe rU�lgpb3eÖf n�ª�n ® cGs�cjg�½fhi}�ys�|�eEn}dtcGsB½ ® escjk�fhi}r]ª�ilrynwg&eE|zc�k~g&i�dt� ® d e�ÄO�3e k�g>§Oe rydtcji}k�d « i}r1uv�ogp�3r&e ® ��dçªorpilg&i�fhi@s�d'¬´n

�3ilrQ������d e r�|bÛ@}��ÜÖ¹'}Vgpr8n}fheEd���nl|3|�cjkytO�£wÛdpf8b3eE|��ysjc�kyt�rpe�|~��fheEdaø�eEnEk;k3i}k3��fhi@ø¼ªo�3gpesgpcGø{eEd ® ½sje�dpdAg&b�nwk���ÝIuvilrT� ¡ � � � ¡ ��¦5�����Q� �y� �a�=� ��  �a�,�Únwk�| �� ,¡ �a�>nH�3ilrT�w�v��dteUrQgpr8n}fheEd���gpb3e�ª�e rp�uvilr�ø6nwk�fheQiwu�� ¡ � � cGø¼ª3r&i�§OeEd1�¥ªqgpiË�Mn�qÝÜnwk�|Õgpb3e{¦�¨aÚ#� ® nld eE|qn�sBtli}rpcjg&byø6d�cGøŪ3rpi�§Oe��'Þ£�£ÝIuvi}rø6n�À~cBøV�yøÏf�i@ø¼ø6nEk�|zÄO�3e �oe,sjeUkytlg&b�d#iwuÖ���E��i}rDtlr&eEnwg&e r�n�r�ø6n�À~cBøQ�yø ÄO�3e �oe�sje kyt}gpb.iEu��Z¨¼ª3rpe �§Oe k�g8d�d i@ø�e�bocGtlbOª3rpc�ilr&cjg�½Vr&e�ÄO�3eEdtgydKuvrpiEø ÄO�3c�f'�8sG½Qr&eEnlf8b3cjk¥tQgpb3es|~c�dW��� ® n}dteE|?dpf8b3eE|~�¥sje rZnHu#il� ® sjcjk¥tgpboe�k~�¥ø ® e r�iEu���dte ryd,n�ª¥ª3rpi�À�cGø6nEgpe�sB½Q|~i}� ® sje�d,gpb3eDª�e r uvilr�ø6nwk�f�e#cBø¼ª3rpi�§Oe�ø�e�k~g�iwuì�£wmdpf8b3eE|��ysjc�kytyn÷;eEnEk;rpe�dWª�ilk�d eQgpcBø�eEdKuvilr�� ¡ � � |~r&i@ª.�yª.g&i¼qÝÙuvi}r�fhi}kM¿ t}�3r8nEgpcji}k�dD¾�cjg&bzø6n�À~cBøV�yøÏf�i@ø¼ø6nEk�|ÄO�3e �3e�s�e kytlg&b�d�iwu����E�zi}r�t}rpeEnEgpe rZnR÷;eEnwk.r&eEdWª�ilk�dte�gpcGø{eEdÐuvi}rs¦�¨aÚ#� ® nldte�|¤nEk�| ��  �a��� ® n}dteE|/n�sj�tli}rpc�gpbyø6dQ|�eEfhrpe�nldte ® ½/�yªg&iä�£ÝÅnÂ�3ilr�|bÛ@}��ÜÖ¹'}ʾ,ilr��Ms�iOn}|3d^iEus�yªg&iÊ¡q��dte rydh��|~c�dW�odɾ�c�gpb�nø6n�À~cBøV�yømfhiEø¼ø6nwk�|,ÄO�3e �3eas�e kytlg&bViEuX�Z�@��ªorpi�§~c�|~e,g&b3e�dpn�ø{easje�§Oe�sOiEu�ª�e r uvilr]ø�nwk�fhe�n}d,|~c�dW�od5¾�cjg&b�3k ® il�3k�|�eE|;fhiEø¼ø6nEk�|³ÄO�3e �oeEd/n

��cGt}�3rpe�dD¨Mn3�@q�nEk�|±¨Mn3�@¨³ª3r&eEdteUk~gYª�e rtuvi}r]ø6nEk�fheQ|onwg8nQuvilrT¦�¨aÚ#� ® n}dteE|±�wÝd&f�b3e�|~�ysjc�kytQiwuÆ�E����d e r|bÛE}£��Ü�¹�}gpr8n}fheEd6��dtc�kyt   rpeEd e e���nwk�|��3�ysBsQfhiEø¼ø6nEk�|ÂÄ��oe �3e c�kyt3�TrpeEd�ª�eEfhgpcB§Oe�sG½¦n ��cGt}�3rpeEdO¨Mn3�£onwk�|º¨8n��E�Òª3r&eEdteUk~g£fhilr&rpeEd�ªÞi}k�|~c�kytq|onwg8n;uvilr ��  �a��� ® n}dteE|ß�£wßdpf8b3eE|~�ys�cjkyt¥n�r_sGsXiwu�gpboez�w�n�sGtli}�

Page 144: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�����

�#i�dtg&�(¨�n}dteE| u#c�dW���(¨�n}dteE|� f n�sje r �� ,¡ �a� « ¨¬+n ¡ ��n ¡ � r �� ,¡ �a� « ¨£¬´n �y� �T� ¡ w��Ý�Z�@�

��r8nlf�e �Þn}fhgpi}r ¡ w��Û�   rpeEd e e�� ���¥sGs¡ eZsGsji �@npo#q �l�ZqMn3�@� �}���8n©¡� ���E�Mn3¨@¨� k�n��Oe �@n��Eq �@�8n�¢@� ��¡yn3¢@� �EqMn���¡r#c�rp�1�#d�§ �Mn3q �@�8nj��� �@�Mn3q@� ���@nj�Z�� fhc��?� � �Mn3q ��q8n�q@� �/¡yn3¨�¡ �Z�Mnpo#¢�#ry|~e r �@n3� �@�8n�¢�¡ ���Mn3�@¢ ��onpo#q��e�ª�ilr&g �@n3� �£o¦n�¨@¨ �@�Mn3¢@¨ �E�Mn©¡¦q

« n£¬Æ÷;eEnwkO��eEdWª�i}k�dteT�,cGø�eEd « ø6d+¬

�#i�dtg&�(¨�n}dteE| u#c�dW���(¨�n}dteE|� f n�sje r �� ,¡ �a� « ¨¬+n ¡ ��n ¡ � r �� ,¡ �a� « ¨£¬´n �y� �T� ¡ w��Ý�Z�@�

��r8nlf�e �Þn}fhgpi}r ¡ w��Û�   rpeEd e e�� ���¥sGs¡ eZsGsji �@npo#q ���8n��@� ���Mn3¨�¡ �Z�Mnpo��� k�n��Oe �@n��Eq �/¡¥nj��� ��¨Mn3�@� �8n��E�r#c�rp�1�#d�§ �Mn3q �Mn3¨�¡ �Mn3¨@¢ �En��E�� fhc��?� � �Mn3q �Mn3�@� ¨Mn��/¡ �8n��Eq�#ry|~e r �@n3� �Mn3�@¨ �@n���� �Enj�Z���e�ª�ilr&g �@n3� �Mn3¢@� �@n3�@q �En��E�

«0® ¬ � ÄO��nwr&eE| ¡ iOeh©�fhcje k�g8dXiwuXà=nErpc�nEgpc�ilk

¯ � °��v´zk�µG¤�·   eUrtuvilr�ø6nwk�fhe�÷;e gpr&c�f dQuvilrâ²´�1e�nldti}k�n ® sje�µÂr_t}e � � e k�d cjgpcB§Oe ¡ e k�gpr8n�sjcB¶ eE| � f8b3eE|~��ys�e r8d�n�á�â ãpä�ã8å&ætçlè¼éOê£ëwè�ì í îlï¼ã�ë^ä�ðEâ�ä�ñlïòï¥â ã�íEë�çlè¼å&ì8ó

Page 145: Aggressive Centralized and Distributed Scheduling ofDisk Requests

���E�

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�øÆ÷;eEnEk;ù�eEd úÞi}k�dte£û,cGø�e

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 16CQ = 128CQ = Infinity

÷vü ø�÷;eEnEk;ý�ilk3� ¡ i@ø�úo�3gpesû,cGø{e

°�±�²�þ�³E´;ÿ�µ�À��x·���������¹��~�� Oú�dteUr8dh¾��� ¦�¨�ý#��¨�nldte�|���f8b3eE|����jc�k��������}ilrpc�gpbyø   e rtuvi}r]ø6nEk�fheuvi}r���c�d��od ��cjg&b   r&eEdteUe!� ¡ i@øÅø6nwk�|"���3e �3eUcjk��

Page 146: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#$#

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�øÆ÷;eEnEk;ù�eEd úÞi}k�dte£û,cGø�e

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 16CQ = 128CQ = Infinity

÷vü ø�÷;eEnEk;ý�ilk3� ¡ i@ø�úo�3gpesû,cGø{e

°�±�²�þ�³E´;ÿ�µ�Àoÿ�·���������¹��~�� Oú�dteUr8dh¾��� ¦�¨�ý#��¨�nldte�|���f8b3eE|����jc�k��������}ilrpc�gpbyø   e rtuvi}r]ø6nEk�fheuvi}r���c�d��od ��cjg&b�%��&��� ¡ iEø¼ø6nEk�|'���3e �3eUcjk��

Page 147: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#)(

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

100

200

300

400

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�øÆ÷;eEnEk;ù�eEd úÞi}k�dte£û,cGø�e

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 16CQ = 128CQ = Infinity

÷vü ø�÷;eEnEk;ý�ilk3� ¡ i@ø�úo�3gpesû,cGø{e

°�±�²�þ�³E´;ÿ�µ�À�+x·���������¹��~�, äú�d e r8d�¾-��.%3���/�j�10�k3i)�2�jeE|3�}e4��f8b3eE|~����cjk��������}ilrpc�gpbyø   e r uvilrp�ø�nwk�fhe�uvilr5�#c�d��od6��c�gpb   rpeEd e e!� ¡ i@ø¼ø6nEk�|'���3e �oe cjk��

Page 148: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#$7

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

100

200

300

400

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�øÆ÷;eEnEk;ù�eEd úÞi}k�dte£û,cGø�e

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

CQ = 16CQ = 128CQ = Infinity

÷vü ø�÷;eEnEk;ý�ilk3� ¡ i@ø�úo�3gpesû,cGø{e

°�±�²�þ�³E´;ÿ�µ�À&8�·���������¹��~�, äú�d e r8d�¾-��.%3���/�j�10�k3i)�2�jeE|3�}e4��f8b3eE|~����cjk��������}ilrpc�gpbyø   e r uvilrp�ø�nwk�fhe�uvilr5�#c�d��od6��c�gpb�%3����� ¡ i@ø¼ø6nEk�|'���3e �oe cjk��

Page 149: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#$9

rpc�gpbyø�d�dtb3i)�¢d cGø�c/��nwr=ú�e rtuvi}r]ø6nEk�fheTcGø�úorpi):Oe�ø�e k~g���b3eUk;gpboe,ø6n);~cBøV�yøÏf�i@ø¼ø6nEk�|¼ÄO�3e �3e,��e k��lg&bc�d�c�k�fhrpe�nldte�|=<�÷;eEnwk/rpeEd úÞi}k�dte{gpcGø{eEd#rpc�dte>��cjg&b¤g&b3e"�lr&i)��cjk��§dtg8nEr?:}nwg&cji}k×iEu�g&cGø�e �vk3i}k�fhrpc�gpc�f n@��rpe �ÄO�3eEdtgydh�XnEk�|ºø�e�nwkÕk3ilk3��fhiEø�ú3�3g&ezg&cGø�e�dA|�eEfhrpe�nldteA��cjgpb/gpb3e6cGø{ú3rpi):Oe�ø�e kOg�c�kd e r?:�c�f�eVg&cGø�eEd#uvi}rgpcBø�e ��fhrpc�gpc�fhn)�¥nEk�|zg&cGø�eU�B��cGøQcjg&eE|�rpe#Ä��3e�dtg8d�<

û(k6fhilk�gprynld g,gpiQg&b3eTd cjk��$�je �1Ä��oe �3e�dpf8b3eE|~����e r8dX|~c�dpfh��dpdte�|Vcjk6d eEfhg&cjilkC93<j�$<D���3n@�/��iwuÚgpb3eT|�c�d���� ü nld eE|�� d&f�b3e�|~���jeUr8dAú�e r uvilr�ø ü eEd gE��cjg&bq�3k ü il�3k�|�eE|�fhi@ø¼ø�nwk�|±ÄO�3e �3e�dF<O÷;eEnwkqkoilk3��fhi@ø{ú3�3gpe{gpcGø{eEd|~r&ilúHGFIJKL��b3eUk�gpb3e�ø6n@;�cGøQ�yøØfhiEø¼ø6nEk�|�Ä��oe �3e���e k��lg&b�f8b�nEk��leEdKuvr&i@øÜ�!�$ �gpiQcjkNM�k3cjgPOQ<R%�c�k3cjg&e ��jeUk��lg&b�fhi@øÅø6nwk�|�ÄO�3e �3eEdTcGø�ú�nwcjrÖn.|~c�dP�~� ü nld eE|�dpf8b3eE|~�&�je rTS d_ý�e!;�c ü c/�jc�g�O?|~�orpcjk&� ü �3r8d g8d�iEu�b3e�nU:NOnlf�gpc�:�cjgPOQ<WV�k�fhe�nQ|~c�d���fhiEø¼ø6nwk�|�Ä��3eU�3e�rpe�nlf8b3eEd�cjgyd`ø6n);~cBøV�yøX�je k��}gpb��onwkNO�d � ü d e�Ä��oe k~gXr&e�Ä��oeEdtgydø���dtg���nEcjgÐnwg�gpboe�b3iOd g ÷ eQ<Y��<���c�k6nZ% ¡ %[��|~e!:�c�f�e�|~r&c�:Oe r�ÄO�3e �3e}ø��3k�gpc/�Þg&b3e�i}k3� ü i�nwr8|±ÄO�3e �oe���e k��lg&b|~r&ilú�d ü e!�ji)��g&b3e[ø6n@;�cGø��yø\<Xû�u�b3c/�lb?ú3rpc�ilrpc�gPOVr&e�Ä��oeEdtgyd#nErpe ü �ji�f]�OeE|�nEg#g&b3e�boiOdtgU�3i):Oe r8n)����dPO3d gpe�øú�e rtuvi}r]ø6nEk�fhe=ø�nUO�dt�N^¥eUr!<W%3i}r�dti@ø{eKiEu3g&b3e_ w�v��dteUr�g&r8nlf�eEdh�}n#|�c�d��Öfhi@ø¼ø�nwk�|YÄ��oe �3eW��e k��lg&b�iEu=GU`�`#i}rø�i}rpe�c�d,k3eEfheEd&dpnEr?O�g&iVú3r&e!:Oe k�g�Ä��3eU�3e cjk&�QiwuÚrpe�ÄO�3eEd g8d�nwg�gpboeAboiOdtgT<

%3ilrÕn@�/�Qfhi}k3M��}�3r8nEgpcji}k�dh���� d&f�boeE|~����cjk��a��cjgpbmgpb3e-% ¡ %[����¦�¨�ý#� ü nld eE|¥�Tilr;uv���/�j�b�~k3i)�2��eE|3�len@�/�li}rpcjg&byø6d�cBø�ú3rpi):OeEd�úÞeUrtuvilr�ø6nwk�fhe6i@:OeUr�gpboe;d cjk��$�je �1ÄO�3e �3e�cBø�ú���e�ø�e�k~gynwgpc�ilk�dT|~c�dpfh��dpdte�|�c�k�dteEfh�gpc�ilk>9N<j��<c�3<cdZ%�i}rXn_ø6n);~cBøQ�yø Ä��3eU�3e ��e k��lg&b�iEuX�!�$ ~�N���dpf8b3eE|����jc�k���|�eEfhrpe�nldte�düø�e�nwk�koilk3��fhi@ø{ú3�3gpegpcBø�eEd ü OeGFI��!`KA<

%3ilrR w�v��d e r[��������¹��,gprynlfhe�dh������û2%�ú3r&i):~c�|~eEd¥gpboeW�ji)�,e�dtg�ø�eEnEk#koilk3��fhi@ø{ú3�3gpeXg&cGø�eEd�< ¡ ��¦fV,Vg0ilrZ�   û2%�� ü n}dteE|qd&f�boeE|~����cjk���r&eEdt�&�jg8d�cjk/nwú3ú3r&i);~cBø6nwg&e!��O.�$<D7QKh�jilk&�le r[ø�eEnEk;k3i}k3��fhi@ø�úo�3gpeQg&cGø�eEd����cjg&b�% ¡ %[��g&r8nwc/�jc�k�� ü O{nwk§nl|3|�cjgpc�ilk�n)�,�$<D7QK"<

û,b3e ü e k3eFM�gydziEu\�Q� dpf8b3eE|����jc�k���nwrpe-��eEdpd?dtc��}k3ciMÞf nwk�gzuvi}r;gpboe͸X»Qj�kml8¹?n]n"�=ilro�3��iOnl|m<p%�c��l��3r&eEd,93<D�$JUI93<D#$�;ú3rpe�dte k�gTúÞeUrtuvilr�ø6nwk�fhe�|3nwgyn�uvi}r�¦�¨�ý�� ü n}dteE|/nwk�|;uv�������B��k3i)�2�je�|3�le>�Q�`d&f�boeE|~����cjk����cjg&b   rpe�dte e!��nwk�|�%��&����fhiEø¼ø6nwk�|³ÄO�3e �3eUcjk��{fhilkNM��l�3rynwg&cjilk�dF<Y÷;eEnwk6r&eEdtú�ilk�dteQgpcBø�eEdXcjk�fhr&eEnld esn@�j�ø�i�dtgXnEkVi}r8|~e rXiEu�ø�n@�lkocjgp��|~e�nld�gpboeaø6n@;�cGø��yømfhi@ø¼ø�nwk�|�Ä��3eU�3e2�je k&�lgpbQr&eEnlf8b3eEd�cjk3M�kocjgPOQ<Xú#k���c��Oe�m�$����¹��~��gpb3e§¸X»Qj�kml�¹?n]n=gprynlfheEd5�Onwc�ke��cjgpgo�je ü e k3eFM�g1uvr&i@øÜn³ø6n);~cBøQ�yøÏfhi@øÅø6nwk�|�ÄO�3e �3e,��e k��lg&b�lr&eEnwg&e rQgpb�nwk��!�$ 3<aqr:OeUk4��cjg&bs% ¡ %[�/dpf8b3eE|����jc�k��3��gpb3e�ø6n);~cBøV�yø�k��yø ü eUr�iwu�il�og8dtgynwk�|�cjk��Õrpe �ÄO�3eEdtgydTnwgQnEk3O.ú�i}cjk�gAc�k¤g&b3e/¸X»Qj�kml�¹?n]n�gprynlfhe�dÖc�d�ilk��/O��!9�# ÷ uvilrTgpboeVcBø�ú��jeZøVe k�g8nEgpc�ilk�d�dtg&��|~cje�|Þø]<��Ød&f�boeE|~����cjk�����cjgpb?n�ø6n@;�cGø��yøÛfhi@ø¼ø�nwk�|RÄ��oe �3e,�je k&�lgpb6iEu��T�� Vú3r&i):~c�|~eEd,n�d���c��}b~g ÷ �tIN�QKVøÐ|~e �fhr&eEnld e#c�k�gpi}g8n@�xrp�3k{gpcGø{eEdÓuvi}r,g&b3eTfhiEø�ú3rpe�dpdtc�ilk>�,i}r?�N�jiOn}|=<Xû,b3e�r&�3k�gpcGø{eEd¿uvilr ü ilgpbH�   û2%�� ü n}dteE|n@�/�li}rpcjg&byø6dTnwr&e��3úÕgpiu#K�u�nldtg&e r�g&b�nwk�% ¡ %[�§nwk�|�g&b3e{¦�¨�ý#� ü nldte�|qn@�/�lilr&cjg&byø6dF<A���jg&b3il�&�lbqg&b3enl|N:lnEk~gyn@�}e#iEuf�   û2%�� ü n}dteE|�n@�/�li}rpcjg&byø6d�c�d5ø{cjk3cBø�n)����b3e k�d&f�boeE|~����cjk���uvilrT¸X»Qj�kml8¹?n]n��Egpb3e!Osú3rpi):�c�|~en�øV��f8b�b3c��}b3e raø6nEr?�lc�k�iwu�úÞeUrtuvilr�ø6nwk�fhe�cGø{ú3rpi):Oe�ø�ehk�g�uvi}r#b3e�nU:�cjeUr �,i}r?�N�ji�nl|3d�<

v ������� ³E±bw ���yx ±��EÑ��ÓÒwÑ�´�Ô�þ���± � ² � ���EÑ�´ez � w��û�n ü �jeg93<Y(�ú3r&eEdteUk~gyd�nwú3ú&�jc�fUnwgpc�ilk3��dtú�eEf�ciMxf�ú�e rtuvi}r]ø6nEk�fhe�|3nEg8nÖuvi}r,{prpe�nldti}k�n ü �je)|�b3i�dtg&� ü n}dteE|{nwk�|

|~c�d���� ü n}dteE|.f�e k~g&r8n)�jc�}UeE|"��Ûdpf8b3eE|����jc�k��Qiwu~ w�v��d e rE�m�$����¹���nwk�|�¸X»Qj�kml8¹?n]n�<2%3ilr��m������¹����Þg&b3eb3i�dtgp� ü n}dteE|.d&f�b3e�|~���jeUr8d,ú3r&i@:�c�|�e�gpb3e ü eEdtg�ú�e rtuvi}r]ø6nEk�fhe ü eEf nE��dtesiwuXg&b3e,�jcBø�cjg&eE|Vf�i@ø¼ø6nEk�|¼ÄO�3e �3e�jeUk��lg&b;cGø{úÞi�dteE|�i}k;gpboeQ|~c�d���� ü n}dteE|.d&f�boeE|~����e r8d�<[��c�gpb;�ok ü il�ok�|~eE|.fhiEø¼ø6nEk�|¼ÄO�3e �3eEd��3gpb3e£|~c�dP�~�ü n}dteE|Õdpf8b3eE|~�&�je ryd1i ü g8nEcjk/n³ø6nwro�lc�k�n@��ú�e r uvilr�ø6nwk�f�eQnl|N:lnEk~gyn@�}eQ<Qû,b3eÕ¸X»Qj�kml8¹?n]n�gprynlfhe�d�nwr&e ü eEd gdteUr?:OeE| ü O�nQ|�c�d���� ü nld eE|�dpf8b3eE|����je rU�Odtc�k�fhe�g&b3e�úÞeUk�|~cjk&�Qrpe�ÄO�3eEd g>ÄO�3e �oeEd�uvilr�¸X»Qj�kml�¹on]n�nErpe���dt��n)����Odtboilrpg�e k3i}���lb?gpi{fhi@ø{ú��je g&e!��O,M�g�cjk�gpiQg&b3eTilk3� ü iOnEr8|.fhiEø¼ø6nwk�|³ÄO�3e �3e�dF<�����/�P���]�$�B�)�m�B�D�)���D�(�b�F�)�P�)���B�c�2�@���t�b�D���f�b�)�@�&�@�b�)�!�$���R�t�)�����]�D���@�Q�b�P�B�)�D�b�o�F�D�_�B�$�]�����b�g�t�D�c���Q�T�@�2�$�P���t�m�b���]�b�!�B�

�]�B�5�������)�D�P�b�?�E�$�������b�2�B�)�5�@�b�)���P�B� ��¡$�]�-�5�)�!���&���]�D�b�?¢g£!���2�$�]�F�,¤�¤o¥��D�Z�b�?���b�D���>¦@¢D¤�¢¨§ �/�F�_���!�P�����b�D�)�B�c�F�>�t�©�B�)�D��)�)���)�����P�)���3¢

Page 150: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#QG

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

100

200

300

400

500

600

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�ø~ª;eEnEk;ù�eEd úÞi}k�dte£û,c�«�e

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

¬ CQ = 16CQ = 128CQ = Infinity

÷vü ø_ª;eEnEk;ý�ilk3� ¡ i�«�úo�3gpesû,c�«{e

°�±�²�þ�³E´;ÿ�µ�À&­�·�¸X»Qj�kml8¹?n]n�¾���Û¦�¨�ý#��¨�nld eE|e��f�boeE|~����cjk��>���/�li}rpcjg&b�«   eUrtuvilro«6nwk�fhe#uvilrg�#c�d��od��c�gpb   rpeEd e e!� ¡ i$«"«6nEk�|C���3eU�3e cjk&�

Page 151: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#$

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

100

200

300

400

500

600

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�ø~ª;eEnEk;ù�eEd úÞi}k�dte£û,c�«�e

FCFS C-LOOKô SSTFõ 2Q FCFS 2Q C-LOOK 2Q SSTFõScheduling Algorithmö

0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

¬ CQ = 16CQ = 128CQ = Infinity

÷vü ø_ª;eEnEk;ý�ilk3� ¡ i�«�úo�3gpesû,c�«{e

°�±�²�þ�³E´;ÿ�µ�®�¯�·�¸X»Qj�kml8¹?n]n�¾���Û¦�¨�ý#��¨�nld eE|e��f�boeE|~����cjk��>���/�li}rpcjg&b�«   eUrtuvilro«6nwk�fhe#uvilrg�#c�d��od��c�gpb�%3����� ¡ i$«"«6nEk�|C���3eU�3e cjk&�

Page 152: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�!#$J

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�ø~ª;eEnEk;ù�eEd úÞi}k�dte£û,c�«�e

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

¬ CQ = 16CQ = 128CQ = Infinity

÷vü ø_ª;eEnEk;ý�ilk3� ¡ i�«�úo�3gpesû,c�«{e

°�±�²�þ�³E´;ÿ�µ�®�¶�·�¸X»Qj�kml8¹?n]n�¾4�Q�.%3��������0�k3i)�2��eE|3�le°��f8b3eE|~����cjk��±���/�lilr&cjg&b�«   eUrtuvilro«6nwk�fhezuvi}r��c�d��od ��cjg&b   rpe�dte e!� ¡ i�«A«6nwk�|\�#�oe �3e c�k��

Page 153: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�F(²`

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 16CQ = 128CQ = Infinity

÷ n�ø~ª;eEnEk;ù�eEd úÞi}k�dte£û,c�«�e

C-LOOKô 2Q C-LOOK SPTF SPCTF* 2Q SPTFõ 2Q SPCTF

Scheduling Algorithmö0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

¬ CQ = 16CQ = 128CQ = Infinity

÷vü ø_ª;eEnEk;ý�ilk3� ¡ i�«�úo�3gpesû,c�«{e

°�±�²�þ�³E´;ÿ�µ�®¥Àx·�¸X»Qj�kml8¹?n]n�¾4�Q�.%3��������0�k3i)�2��eE|3�le°��f8b3eE|~����cjk��±���/�lilr&cjg&b�«   eUrtuvilro«6nwk�fhezuvi}r��c�d��od ��cjg&bH%3���/� ¡ i�«A«6nwk�|\�#�oe �3e c�k��

Page 154: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�F(o�

³#i�dtgp��¨�nld eE| ��c�d�����¨�nldte�|¥� ¡ �L´Û�!�� û�r8n}fhe ¡ �µ´Ï�   rpe�dte e!� %3�����

�&��û2% < ¡ �¶<·����ù ����û2% ����û2% <·����ù,<i���²� E��¸�d e r ®�®�®�µ �oÿ #�7$#3<c9�� #�7��N<D#)(�QO�k�ù�¹�e k �  ,¡ û2% < ¡ �¶<·����ù �  ,¡ û2% �  ,¡ û2% <·����ù,<i���²�

®�®ÓÀxµ/¯=� #�7QGQ<cJ�7 #�7�9N<j�T7¡ ��¦fV,V�0Z< ¡ �¶<i����ù ¡ ��¦fV�Vg0 ¡ �(¦fV,Vg0Z<i����ù,<i�&�Q�

�!J$#3<DJ)( ¶N­�¯¿µ/®�8 ¶38�8�µ +�¯¡ i$«�ú3rpe�dpd �  ,¡ û2% < ¡ �¶<·����ù �  ,¡ û2% �  ,¡ û2% <·����ù,<i���²��!J$`3<iGU� ¶N8=�¥µ/®�¶ ¶38�ÿ�µ/8ÓÀ

º »�¼R½v´;ÿ�µ�¾�·,ª;eEnEk�ý�ilk3� ¡ i�«�úo�3gpeTû,c/«�eEd ÷ «6d�ø�i}r2�#ú3ú&�jc�fUnwgpc�ilk{ù1�ok6û,c�«�e�d ÷ dteEfEø¿uvi}rE{yù1eEnE�d ilk�n ü �je)| ¡ e k�gpryn@�jc/} eE|>��L��f8b3eE|����je ryd

¿5À�Á5À� Ã�Ä�ÅÆÅÈÇ[ÉNÊÌË ÍHαË6Ï5Ð�Ñ?Ä5Ò�ÓPË2Ï5Ò��|3|~c�k��{n@�leU�(d e k�dtc�gpc/:~c�g�O{gpi\�   û2%�� ü nldte�|.n@���}ilr&cjgpb&«6d1c/«�ú���e!«Ve�k�gpeE|Qcjk§|~c�dP�~� ü nld eE|;d&f�boeE|~����e r8d

c�«{ú3rpi):OeEd�dtgynwr?:}nEgpcji}kqrpe�dtc�d g8nEk�fhe ÷ c1< eQ<��Þr&eEdtú�i}k�dte�g&c�«�e�:}nwrpc�nwk�f�elø]<�¨ O.f�ilrpr&eEfhgo��Os{o�,e c/�lb�gpc�k��Q|6n@�}�cjk&�qcjk~uvi}r?«6nEgpc�ilk���gpboe.c�«�ú3r&i):Oe!«VeUkOgQcjk�dtgynwro:lnEgpc�ilk�rpeEd c�dtgynwk�f�eÕ|~iOeEd�k3ilg�dtc��}k3ciMÞf nwk�g?�/O�|~e!�}r8n}|~eú�e rtuvi}r?«6nEk�fheQ<RÔ(k{dti�«{e�f nld eEdh��n@�}e ��dte k�d cjg&c�:�cjgPOQn}fhgp��n)���/O�c�«{ú3rpi):OeEd=«�e�nwkQrpe�dtú�ilk�d e�gpc/«�eEd ü O�«6nwc�k3�g8nEcjk3c�k��;g&b3e�ilr8|�e rpc�k��;iEu�dte�ÄO�3e k�gpc�n@��r&e�Ä��oeEdtgydÖc�dpd �3eE|¤c�kÕ��i��lc�f n@�/��O§nldpf�e k�|~c�k��;i}r8|~e rT<\�#c�dP�~� ü n}dteE|�   û2%d&f�boeE|~����e r8d���cjgpb?n)�le ��dte k�dtcjg&c�:�cjgPO���dt��n)���/O�il�3g&ú�e rtuvi}r?«`g&b3e cjr�boiOdtg&� ü nldte�|.fhil�3k�gpeUrpú�nErpg8d�<

%3ilr6e!;�úÞeUrpc�«{e k~gyd���dtc�k��qg&b3e uv�&����d�OodtgpeT« gprynlfhe�dh���Q� dpf8b3eE|����jc�k��¤c/«�ú3r&i@:Oe�d�i@:OeUr8n@�/��dPO3d gpe!«ú�e rtuvi}r?«6nEk�fhe ÷ n}d�«�eEn}dt�3r&eE| ü O?nEú3ú��jc�f nwg&cji}k3�(d ú�eEfhciMÞfÖú�e r uvilro«6nwk�f�e�«{e gpr&c�f d8ø]<=û,b3c�d#c/«�ú3r&i@:OeT«Ve�k~grpe�dt����g8d1uvr&i�«Ö�}c�:�cjk���ú3r&cjilr&cjgPO6gpi6gpc/«�e ��fhrpc�gpc�f n)��nwk�| g&c�«�e �b�jc/«Qcjg&eE|Vrpe#Ä��3e�dtg8d�<Tû,c�«�eU��k3i}k�fhr&cjgpc�f n@�xrpe �ÄO�3eEdtgyd�nwr&e�iwuvg&e k?dtgynwr?:Oe�|¥�~r&eEdt����gpc�k��Qcjk\«���f�b�b3c/�lb3e r2«{eEnwk�r&e�ÄO�3eEdtg�r&eEdtú�i}k�dtesgpc�«{eEdF<

%�cjkocjgpe{fhi$«"«6nwk�|ÊÄO�3e �3eA�je k��}gpb�dTc�«�ú�nwcjrTg&b3e�×�e!;�c ü c��jc�gPO;iwuÖ|~c�d���� ü n}dteE|-�Q��dpf8b3eE|����je rydF<H%3i}rb3eEn!:NOÕ�=ilro�3��iOnl|odh�,b3c/�lb�ú3r&cjilr&cjgPOÕrpe�ÄO�3eEd g8d�«�nUOÕb�n!:Oe�g&iH��nwc�g�nwgQg&b3e6b3iOd g ü eEf nE��dte6iEu#uv���/�,i}k3�ü iOnEr8|Qfhi$«"«6nwk�|_ÄO�3e �3e�dF<R�#c�dP�~� ü n}dteE|����d&f�boeE|~����e r8d¥i}k���O�i}�3gpú�e r uvilro«ÌboiOdtg&� ü nldte�|E���d&f�boeE|~����e r8d��b3e k?gpb3e�«6n@;�c�«Q�&«Ýk~��« ü e r,iEu=il�3gydtg8nEk�|~c�k���rpe#Ä��3e�dtg8d�|~iOeEd�k3i}g��lr&eEnwgo��O�e!;ofhe e�|�g&b3eE«�n@;�c�«Q��«fhi$«"«6nwk�|³ÄO�3e �3e,��e k��lg&b�<

Page 155: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ØÆÙ ZÛÚÝÜÈÞàß á

â ã@ä©åWæ ã [Õç åWè,é êeë ì�è�é çHí ã)î�ï

�#c�d gpr&c ü �3g&eE|d&f�boeE|~����cjk��.c/«�ú��jc�eEd�gP�,iÕilr>«�ilr&ezeUk~g&cjgpc�eEdQn@��ilk��ÕgpboeHÔp��V�ú�nEgpb�fhiOi}ú�e r8nEgpc�:OeT��OrpeUilr8|�e rpc�k���|~c�dP�#r&e�ÄO�3eEdtgydF<�û,b3c�d�f8b�nwúogpe rxe!;3n)«�cjkoeEd�|~c�d gprpc ü �3g&eE|�dpf8b3eE|����je rxc�«�ú&�je!«�e k�g8nwg&cji}k�d3��b3e r&eb3i�dtgp� ü n}dteE|.d&f�b3e�|~���jeUr8d ÷ eQ<ð�&<j��cjkÕVT�$��|�e!:~c�fheT|~r&c�:Oe ryd�ø=fhiOi}ú�e r8nEgpeE��c�gpb?|~c�d���� ü n}dteE|?dpf8b3eE|~�&�je ryd ÷ c�k|~c�d��sfhilk�gpr&i��/�je ryd�ø]<ñª;iOd g�iwuxgpboe�nl|N:lnEk~gyn@�}eEd�iwuxb3iOd gp� ü nld eE|�nEk�|Q|~c�dP�~� ü n}dteE|QfheUk~g&r8n@��c�} e�|Ad&f�boeE|~����cjk��nwr&e�n)��d iAuvil�ok�|Vcjk{|~c�dtgpr&c ü �ogpeE|Qd&f�b3e�|~���jc�k���<ñqXnlf8b�fhi$«�ú�ilk3eUk~gXd&f�boeE|~����e r�b�n}dKeEn}d�O�nwk�|Vc�«"«{e |~c�nwg&enlfUfheEdpd�gpi"��i�f n@�Xd&f�boeE|~����cjk���cjk~uvi}r?«6nEgpc�ilk�<Tû,b�nEgTc�dh��gpboeQb3iOd gp� ü nld eE|qdpf8b3eE|����je r�b�nld��~koi@�2��eE|3�}eQiwud�Oodtg&e!«¶�li�n@��dXnEk�|ò�}��nwrynwk�gpe e�dh�Q��b3c���e,eEn}f�b£|~c�dP�~� ü n}dteE|Qd&f�b3e�|~���jeUr�b�n}dXnlf fh�or8nwg&e�|~c�d��£fhilk3Mó�l�3rynwgpc�ilknwk�|�dtgynwg&eKc�k~uvilro«6nwg&cji}k�<�û,b3eXb3iOd gp� ü nld eE|�fhi$«�ú�ilk3eUk~g�f nEkTúÞeUrtuvilro«¢dpf8b3eE|����jc�k���ilú3g&c�«�c/}Enwg&cji}k�d�dt��f8bnld�r&e�Ä��oeEdtgTf�ilk�f nEgpe k�nwgpc�ilk�����b3c/�jeQeEn}f�bÕ|�c�d���� ü nld eE|¤f�i�«�ú�ilkoe k~g�f nEkÕ«6n);~c/«�c�}�eTgpb3e�f�ilk�fh�orprpeUk�fFOü e gP�,e eUkzr&e�ÄO�3eEdtgyd,rpeEf�e c�:�cjk��£dte ro:~c�fheQ<�ª;i�dtg�iwu�gpb3e£|~c�d&nl|3:}nwk�g8n)�leEd�iwu�b3iOd gp� ü nld eE|.nwk�|.|�c�d���� ü nld eE|fhe k�gpryn@��c�} eE|Td&f�b3e�|~���jc�k��TnErpe�i ü :~c�nwgpe�| ü O£fhiOilú�e rynwgpc�ilk ü e gP�=e e k�g&b3e�|~c�dtgpr&c ü �ogpeE|Qfhi$«�ú�ilk3eUk~gydF<W%3i}re!;on@«�ú&�jeO�lboiOdtg&� ü nldte�|.dpf8b3eE|~����e r8dXf nEk6g8n@�Oesd gpe ú�d,g&iQrpeE|���fhe�g&b3e�k3e!��nwg&c�:Oe�c/«�ú�nlf�gKiEu��jc/«�cjg&e |Q|�c�d��fhi$«"«6nwk�|³ÄO�3e �3e,��e k��lg&b�d ÷ d e esdteEf�gpcji}kHGQ<D�N<D�Oø]<

û,b3eTilk��/O�|�c�dpn}|3:}nwk�g8n)�le�iEuX|�c�dtg&rpc ü �3gpe�|Vd&f�b3e�|~���jc�k���c�d,gpb3e�k3e eE|Vg&iZ«�i�|~c¼ubOQe!;~c�dtg&cjk��sú3rpi}gpi�fhi$��dgpi�n@����i)��gpb3esk3eEfhe�dpdpnEr?O\�jeT:Oe!��dXiwuÐfhiOilú�e rynwg&cjilk ü e gP�=e e k.d&f�boeE|~����cjk���fhi$«�ú�ilk3eUk~gydF<5��d2��cjgpb§|~c�dP�~�ü n}dteE|�fhe k�gpr8n)�jc/} eE|Õdpf8b3eE|~����cjk��o��nÕd�«6n)���=n@«{il�3k�gQiwuÖd�Oodtg&e!«��b�je!:Oe!��cjk�uvilr?«�nwgpc�ilk4«���d g ü e6ú�nld&dteE|ü e gP�,e eUkAg&b3e,boiOdtg�nwk�|�eEn}f�b£|~c�dP�~� ü n}dteE|Qd&f�b3e�|~���jeUr�gpi�e!;~ú�eE|�cjgpeXb3c/�lbQú3r&cji}rpcjgPO�r&e�ÄO�3eEdtgydF<ñÔ�uogpboe,b3i�dtgdpf8b3eE|����je r�c�d,gpi�r&e ilry|~e r�r&e�Ä��oeEdtgyd ü n}dteE|6ilk.b�nEr8|3�Ðnwr&e �(d ú�eEfhciMÞfÖc�k~uvilro«6nwg&cji}k���dti$«�esfhilk3Mó�l�3rynwgpc�ilknwk�|;dtgynwg&eE��k3i)�2�jeE|3�}e,«V��d g ü e�eT;~g&r8nlf�gpeE|�nEk�|zg&r8nEk�d uve r&rpeE|6gpi�gpb3eTb3i�dtg�nld2�,e!�/��<�³#i)�=e!:Oe r �Oc¼u�g&b3en@«{il�3k�g�iEu�fhilk�gpr&i��,c�k~uvilro«6nwg&cji}k¤r&e�Ä��ocjrpe�| uvilr£fhiOilú�e rynwgpc�ilk�c�d�«{cjk3c/«Vc/} e |x�¥ilk��/OqdP�jc/�lb�g�ú3r&ilgpi�f�i��«�i�|~c·Mxf nEgpcji}k�d�dtboil����| ü esk3eEfheEd&dpnEr?OQ<

�����Ú|~c�dtgpr&c ü �ogpeE|.d&f�b3e�|~���jc�k���e!;~ú�e r&c�«�eUk~gyd,nld&dt��«{eQgpb�nEg�gpb3eQboiOdtg&� ü nldte�|qdpf8b3eE|~�&�je r�b�nld�c�k�dt�~uv�Mxfhc�e k�g6fhi�«{ú3�3g8nEgpc�ilk�rpe�dtil�or8fheEd���b�nwry|3��nErpe ��dtú�eEf�ciMxfH�~koi@�2��eE|3�}eO��nEk�|Þ� i}r.b�nwry|3��nErpe/dt�3úoúÞi}rpg.g&ifhi$«�ú3�3g&e�úÞi�dtc�gpcji}k3cjk&��gpc/«�eEd¿uvi}r�nsdte g=iwu�ú�e k�|~c�k���r&e�ÄO�3eEdtgydF<ñ³#iOd gp� ü nld eE|�dpf8b3eE|����je ryd�cjk�gpb3c�d,f8b�nwú3�gpeUrKg&b3e r&ehuvilr&e#��d e�d cjk��$�je �1ÄO�3e �3e�nEk�|"��ô:Oe rydtc�ilk�d�iwu�g&b3e ¡ �(¦fV,Vg0Z< ¡ �¶<i�&��ù�nwk�|\����û2% < ¡ �¶<i����ùdteUe!�~�vrpe�|~��fhc�k���n)���}ilrpc�gpb�«�dF< ¡ b�nwú3g&e r�7�|~eEd&fhrpc ü eEd#b3i)�Íg&b3eEd eQg��=i6n@�/�li}rpcjg&b�«6d��}e k3e ryn@�/��O6ú3rpi):�c�|~egpboe ü eEdtg�ú�e rtuvi}r?«6nEk�fhe6uvilr{¦�¨�ý#� ü nldte�|�dpf8b3eE|~����cjk��ÕnEgVg&b3e;boiOdtgT<�û,b3e§|~c�d gpr&c ü �3g&eE|d&f�boeE|~����cjk��e!;�ú�e rpc/«�e k�g8d#c�k�fF�j��|~e6|~c�d���� ü n}dteE|�d&f�b3e�|~���jeUr8d���c�gpb�¦�¨�ý#� ü nld eE|�nwk�|quv�������B��k3i)�2�je�|3�le6d&f�boeE|~����cjk��n@�/�li}rpcjg&b�«6d�<2�#c�dP�~� ü n}dteE|?dpf8b3eE|~����e r8d ��c�gpb6uv�������B��k3i)�2�jeE|N�lesn@�/�lilr&cjg&b�«6d�nwr&eQn}dpdt�&«�eE|zg&iVb�nU:Oe£dt�~uv�Mxfhc�e k�g�rpe�dtil�or8fheEd�nwk�|×b�nEr8|3�Ðnwrpe?cjk~uvi}r?«6nEgpc�ilk�gpi/fhi�«{ú3�3gpe{úÞi�dtc�gpcji}k3cjk&�¤g&c�«�eEd�uvilrZM�k3c�gpe �b�je k&�lgpbÄO�3e �3eEd�iwu�ú�e k�|~cjk��?rpe�ÄO�3eEd g8d�<Qû,b3e�e!;~ú�e r&c�«�eUk~gyd,cjk.gpboc�dTf�b�nwú3g&e rTnwr&eVú�nwrpg&cjg&cjilkoeE| ü nldte�| i}k¤g&b3egPO~ú�eTiwuÚcjk�uvilr?«�nwgpc�ilk���dteE| ü O�g&b3esdpf8b3eE|~�&�je rydF<

�F(²�

Page 156: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�F(²#

á"õ!ö êeë_ì�è�é çHí ã)î�ï ÷Öã�å[ì øfî�ùQúZæ û ü,å[ãTú�î ýeæ�ú�û þ _ è í ú,÷ ]û,b3c�dsdteEf�gpcji}kqe!;on@«�c�k3eEd�gpb3e{úÞeUrtuvilro«6nwk�fheViEu�|~c�d gpr&c ü �3g&eE|Õdpf8b3eE|~����e rTc�«�ú&�je!«�ehk�g8nEgpc�ilk�d#��dtcjk&�

|~c�d���� ü n}dteE| ¡ ��¦fV�Vg0Q�f����û2%,�f�  ,¡ û2%,��nEk�|°���  ,¡ û2% ÷ 9Oø]<s¨,ilg&b.gpb3eQb3i�dtg&� ü n}dteE|/nwk�|;g&b3e�|~c�dP�~�ü n}dteE|Õdpf8b3eE|~�&�je ryd#nErpe�gpb3e r&ehuvilr&e�nwg&gpe!«�úogpcjk&�Vg&i'«{cjk3c/«Vc/}he�«{eEnwk.r&eEdtú�ilk�dte�gpc�«{eEd ÷ nEk�| r&eEdtú�i}k�dtegpc/«�e5:lnErpc�nwk�fhe�dh�3cjk6g&b3esf nld eAiEuXgpboe�n)�le ��dteUk�dtc�gpc�:Oe��  ,¡ û2%n@�/�li}rpcjg&b�«;øÿ<

� À�� À�� � ÓPÒ3��������Ä��fÒ����>É�Ç�Ð��fÒ��� �]¼R»�w ´�Ô��ÓÒEÑ�´�Ô�þR½v±���²Õ»����EÑ�´��6±bw��

û,b3eQe!;�ú�e rpc/«�e k�g8d�rpe ú�i}rpgpe�| ü eT�ji)��e!;on@«�c�k3e�g&b3eQú�e rtuvi}r?«6nEk�fheTeF^xeEfhgyd1iEu�d e�ÄO�3e k�gpc�n)��dpf8b3eE|~�&�j�cjk&��iwuÚrpe�nl|�nEk�|"��rpcjg&e#r&e�ÄO�3eEdtgydKi}k;|�c�d���� ü nld eE|'����û2%qc/«�ú��jeT«Ve kOgynwg&cjilk�dF< ¡ �(¦fV,Vg0Ìc�dK�3k�nU^xeEfhg&eE|ü OQgpb3eTd e�ÄO�3e k�gpc�n)�xdpf8b3eE|~����cjk��Ti}ú3gpc/«�c�}EnEgpc�ilk��Od cjk�f�e#c�g,n)�jr&eEnl|3O{dpf8b3eE|����jeEd�r&e�Ä��oeEdtgydKcjk>�ji$�lc�f n@�/��O�nld �fhe k�|~cjk���ilry|~e rT< �Oe�ÄO�3e k�gpc�n)��dpf8b3eE|~�&�jcjk&�#iEu¥r&eEnl|�r&e�ÄO�3eEdtgyd�nEgXgpb3eÐ|~c�dP�Qfhi}k�dtc�dtgpeUk~go��O�c/«�ú3rpi):OeEdf�&��û2%ú�e rtuvi}r?«6nEk�fheO�}eEdtú�eEfhc�n@�/��O�uvilr=fhi}k3M��l�or8nwg&cji}k�d[��c�gpbZ��nEr?�}e�«6n);~c/«V�&«�fhi$«"«6nEk�|,ÄO�3e �3e2��e k��}gpb�d�<[�Oe �ÄO�3e k�gpc�n)�3d&f�boeE|~����cjk���iwum��rpc�gpe�r&e�Ä��oeEdtgydf«6nwro�lc�k�n@�/��OT|~eT�lr8n}|~eEd�ú�e rtuvi}r?«6nEk�fheXuvilrX|~c�d��odf��cjg&b   rpeEd e e!�fhi$«"«6nwk�|³ÄO�3e �3eUcjk���nEk�|�c�«�ú3r&i):OeEd�úÞeUrtuvilro«6nwk�fhe#uvilr�|�c�d��od ��cjg&b�%��&����f�i�«"«6nEk�|RÄ��3eU�3e cjk&��<Xû,b3c�d«6nEg8f8b3eEd�gpb3eQú3r&e!:�cjil��d#i ü d e r?:}nEgpcji}k¤g&b�nwgsd e�Ä��oe k~g&c�n)��d&f�b3e�|~���jc�k���iwu2��r&cjg&eEd�nl|N:Oe r8d e!��O?nU^xeEf�g8d#g&b3eú�e rtuvi}r?«6nEk�fhesiwuÐ|~c�dP�3d5��cjgpboil�3g���r&cjg&eQú3rpe ü �3^xe rpc�k�� ÷ d e e�ú�n@�leA7~�Qc�k.dte�fhgpc�ilk°73<���<c�^uvilrTnVuv���/��|�c�dt�fh��d&dtc�ilk;iEu�g&b3c�d ü e b�nU:�cji}rhøÿ<

%�c��}�3rpe�dCG²<j�tI&GQ<c9q|~c�d ú���n!O-«�eEnEkqrpe�dtú�ilk�d e.gpc/«�eEdÖuvi}r6|~c�dtgpr&c ü �ogpeE|�dpf8b3eE|����jc�k��.iwusgpboe.dtc/;-³  nwk�|à�gq ¡ �,i}r?�N�ji�nl|3d�< û,boeEdteÕMó�l�3r&eEd.dtb3i)� gpb3e/c�«�ú3r&i):Oe!«VeUk~g ÷ i}rÕ|~e!�lrynl|3nEgpc�ilk¥ø?f nE��dte�| ü Onl|o|~cjk���dte�ÄO�3e k�gpc�n@��dpf8b3eE|~����cjk��Õiwusr&eEnl|3d{nwk�|s��r&cjgpe�d^g&i�n�|~c�dP�~� ü nld eE| ����û2%Ýd&f�boeE|~����e r!<ôqXnlf8b�lrynwú3b dtb3i)��d6|3nwgyn�uvi}r�uvi}�3r?fhilkNM��l�3rynwg&cjilk�dh�Tfhi$«�ú�nwr&cjk��±«6n@;�c�«���« fhi�«"«�nwk�|ßÄ��3eU�3eH�je k&�lgpb�diwu��T9znEk�|q�!�$ VuvilrT|~c�d��od���cjg&b;e c�gpb3eUr   rpe�dte e!�6i}r,%3�����Úfhi�«A«6nwk�|�ÄO�3e �3eUcjk��&<���cjg&b.n�b3i�dtgp� ü n}dteE|¡ ��¦fV�Vg0Z< ¡ �¶<·����ùÝd&f�b3e�|~���jeUr �xdte�ÄO�3e k�gpc�n@�Údpf8b3eE|~����cjk��{iwu�r&eEnl|.rpe#Ä��3e�dtg8d ü O§nz|�c�d���� ü nld eE|��&��û2%dpf8b3eE|����je rs|~e�fhrpeEn}dteEd,«�eEnEkqrpeEd ú�ilk�d ezg&c�«�e�d ü OÕ�3úqgpi°�)(3K nEk�|-#�7QKIuvilrZ«6n);~c/«V�&«If�i�«"«6nEk�|ÄO�3e �3e>�je k&�lgpb�dAiwu£�!9?nwk�|��T�� ~�Xrpe�dtú�eEfhg&c�:Oe!�/O ÷ ��dtc�k��;g&b3e6d e!�jeEf�gpeE|.gprynlfhe{dpf n)�jc�k��zu�n}fhgpi}r8d�øÿ<e��cjg&bn¤b3i�dtg&� ü n}dteE| ����û2%_< ¡ �¶<i�&��ùId&f�b3e�|~���jeUr �,g&b3ee«�e�nwkr&eEdtú�i}k�dte.g&c�«�eEdQ|�eEfhrpe�nldte ü O��3ú�g&ia#�`Knwk�| #$9KA<Ý%3i}rzeT;~ú�e r&c�«�e k�g8d���dtcjk&�s%3���/�Tfhi$«"«6nwk�|âÄO�3e �3e c�k��3��d e�Ä��oe k~g&c�n)����O�d&f�b3e�|~���jc�k��4��r&cjgperpe#Ä��3e�dtg8dKuv�orpgpboe r�|~eEfhr&eEnld eEd «�eEnEk�rpe�dtú�ilk�d e�g&c�«�eEd ü O��3ú6gpi?��<c7KA<

��dKg&b3e,�m�3ÁwÂO¹��,i}r?�N�ji�nl|Vc�d ü e gpg&e r=dte ro:OeE| ü O�nTb3iOd gp� ü nld eE|6dpf8b3eE|~����e rXgpb�nEg�fhi}k�f nEgpe k�nEgpeEdXrpeEn}|rpe#Ä��3e�dtg8d ÷ rynwg&b3e r�g&b�nwkÕd e�Ä��oe k~g&c�n)����O{dpf8b3eE|����jc�k��Vg&b3e!«;øy�M��}�3rpe"G²<iGQúorpi):~c�|~eEd�nl|3|�cjgpc�ilk�n)��|onwg8nVuvi}r|~c�dtgpr&c ü �ogpeE|�dpf8b3eE|~����cjk��/��dtc�k��qb3i�dtgp� ü n}dteE| ¡ ��¦fV,Vg0ò< ¡ �¶< ¡ ùÜnwk�| ����û2% < ¡ �¶< ¡ ù,<,û,boeH«�eEnwkrpe�dtú�ilk�d e�gpc/«�eEd1uvi}rTgpb3e6f�ilk3M��}�3r8nEgpc�ilk�d,��cjgpb�nC«�n@;�c�«���«�fhi$«"«6nwk�|±Ä��3eU�3eZ�je k&�lgpb/iwuT�T9;|~r&ilúnwúoú3rpi);�c�«6nEgpe!�/OZJKÈ��b3e k�g&b3e�b3i�dtgp� ü n}dteE|?dpf8b3eE|~����e r=fhilk�f nwg&e k�nwg&eEd,rpe�nl|3d,c�k�dtg&eEnl|ViEuXd e�ÄO�3e k�gpc�n)���/Odpf8b3eE|����jc�k���gpb3eT«H< ¡ ilkNM��l�3rynwg&cjilk�dr��c�gpb£n6«6n);~c/«Q��«þÄO�3e �3e��jeUk��lg&b�iwu¿�!�� 5�Onwc�kE��cjgpgo�je ü e koeFM�g�uvrpi�«gpboc�dTf�b�nwk��}eO��n}dAgpboeVb3i�dtgsilk��/OÕfhilk�fUnwgpeUk�nwg&eEdAr&e�Ä��oeEdtgyd���b3e kqg&b3e{|~c�dP�Õdt� ü dPO3d gpe!«*c�d�e!;~g&rpe!«{e!��Oü ��dPO ÷ c1< eQ<��3��b3eUk'«{ilrpe�gpb�nEkq�!�$J^r&e�ÄO�3eEdtgyd�nwr&eAi}�3g8d g8nEk�|~cjk&�Vuvilr�n�dtc�k�����e�|�c�d���ø]<

°�þR½B½�������� x ½�´�Ô�²Þ´���ÒEÑ�´~Ô�þR½�± ��²°»!�"�EÑ�´��6±Bw#��  ,¡ û2%�nEk�|H���  ,¡ û2% ÷ 9�ø�e!;�ú�e rpc�e k�fheTgpboe�dpn@«{eE�leUk3e r8n)��r&eEnlf�gpcji}k.gpi6d e�ÄO�3e k�gpc�n)��d&f�boeE|~����cjk��

iwu�rpe�nl|�nwk�|-��rpc�gpe�r&e�Ä��oeEdtgydF<4%�c��l�orpeEd�G²<D UI&GQ<��F(/|~c�d ú���n!O°«�eEnwk/rpeEd úÞi}k�dte?gpc/«�eEd#uvilr�|~c�dtg&rpc ü �3gpeE|c�«{ú��je!«�e k�g8nEgpc¼ilk�d���d cjk��s|~c�d���� ü n}dteE|\�  ,¡ û2%¤d&f�b3e�|~���jc�k���<Úû,b3e!O£dtb3i)��gpb�nwg=dte�ÄO�3e k�gpc�n@��d&f�boeE|~����cjk��

Page 157: Aggressive Centralized and Distributed Scheduling ofDisk Requests

�F($(

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

25

50

75

100

125

150

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

25

50

75

100

125

150

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBA<C +ED�FHG�IJLKMK:NPORQ$<iGU7TS�U��*VW+���/;1 ' +32<4e����û2%YXB2�Z3[ )\Z?« '<]H^ 2

Page 158: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QF(²7

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBATCH+ED`_EG��m�baTc,J�OBQ�<D�$7TS�U���V�+���/(1 ' +3254u�&��û2%dX�2#Z3[ )PZo« 'T]e^ 2

Page 159: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QF(²9

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?> @�þ�A<C +ED/®�G*fhg ljib��n#klO��N<D7<S�U��*VW+���/;1 ' +32<4H����û2%mX�2�Z.[ )PZo« 'T]H^ 2

Page 160: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QF(NG

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBA<C +ED�¾�G��on�gMi È=�HOm�3<c7TS�U��*VW+���/;1 ' +32<4e����û2%dX�2�Z.[ )PZo« 'T]H^ 2

Page 161: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QF(²

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

50

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

50

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?> @ÞþBA<C +ED �pGrq2l0s!J�l�Q�<D`<S�U���V�+���/(1 ' +3254 ����û2%mX�2#Z3[ )PZo« 'T]e^ 2

Page 162: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QF(²J

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?> @ÞþBA<C +ED�ÿtG5�uJ�kbNQl�v�OEQ�<D`<S�U���V�+���/(1 ' +3254 ����û2%mX�2#Z3[ )PZo« 'T]e^ 2

Page 163: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$`

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø_³*)w+3-0/(1 ' +.2<4x68/(9fV,Vg0ò<:6��¶<y6=ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<y6=ù

=?>�@�þBATCH+ED +EG��m�baTc,J�OBQ�<D�$7TS�U���V�+���/(1 ' +3254u�&��û2%dX�2#Z3[ )PZo« 'T]e^ 2

Page 164: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7�Q

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

20

40

60

80

100

120

140

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

20

40

60

80

100

120

140

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBA<C +ED�8�GzIJ�KMK{NPORQ�<·G)7TSrU��*V�+P�!/(1 ' +.2<4e��X6=û2%dX�2�Z.[ )PZo« 'T]H^ 2

Page 165: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$�

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?> @ÞþBA<C +ED/­tG5�m�|aTc,J�OBQ�<c��7<S�U��*V�+P�!/(1 ' +.2<4 �}X~6=û2%mX�2#Z3[ )PZo« 'T]e^ 2

Page 166: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$#

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

5

10

15

20

25

30

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

5

10

15

20

25

30

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBA<C +ED�FN¯�G*fhg l�iB�5n#klO��N<D7TSrU��*V�+P�!/(1 ' +.2<4e��X6=û2%dX�2�Z.[ )PZo« 'T]H^ 2

Page 167: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7)(

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

5

10

15

20

25

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

5

10

15

20

25

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBA<C +ED�FHFHG��En#gMi È=�HOm�3<D7<S�U��*VW+���/;1 ' +32<4e��X6=û2%dXB2�Z3[ )\Z?« '<]H^ 2

Page 168: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$7

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

5

10

15

20

25

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

5

10

15

20

25

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?> @�þ�A<CH+pD F|_EG�q2l0s!JtljOEQ�<D`<S�U��*VW+���/;1 ' +32<4e��X6=û2%dXB2�Z3[ )\Z?« '<]H^ 2

Page 169: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$9

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø~³*),+.-0/(1 ' +3254768/(9fV,Vg0ò<:6��¶<i����ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<i����ù

=?>�@�þBATCH+ED�FN®�G��uJ1k|NQl�v OoQ$<D`<S�U��*V�+P�!/(1 ' +.2<4e��X6=û2%dX�2#Z3[ )PZo« 'T]e^ 2

Page 170: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7QG

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷(' ø_³*)w+3-0/(1 ' +.2<4x68/(9fV,Vg0ò<:6��¶<y6=ù

CQ = 16 CQ = 128 CQ = 16 CQ = 128

Maximum Command Queue Length$0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

No Opt.SSR.SSW.SSR

Preseek% Full&

÷�ü ø_³�),+3-�/;1 ' +32<4H����û2% <:6��¶<y6=ù

=?>�@�þBATCH+ED�FN¾�G��m�|aTcwJ�O�Q$<D�$7TS�U��*VW+���/;1 ' +32<4H��X6=û2%mX�2�Z3[ )\Z?« '<]H^ 2

Page 171: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$

)T[�Z�2 ' 4�Z�2�Ä}�b2<+3-L+6�?V�-0� ' 4!VW+���/ üe' +3254Õ��XXû2%�+ ^ �|2<4!����2�Z?V�«{ú 'P^ -L+ «�2 '<] Z025+túH) ] +.2�-0V/«�2<+ ü O�Q)K�)\Z�M25+0+F<,�,2�Ä,�|2 ] -0V ' ��+ ^ �|2<4!����V ] �")T[_�?Z�VM-02zZ02�Ä,�|2<+.-�+�4!2!�\Z ' 4�2<+#úH2�Z3[ )\Z?« '<]H^ 2 ü O �3ú�-�)\�3<Y(3K�[ )\Z�4!VW+��b+�?VM-���XRZ02<+.2�2!� ^ )�«A« 'T] 4�Ä,�|2��|2#V ] �&<��*VW+��b+��?VM-��°%e�&��� ^ )�«"« 'T] 4�Ä,�|2��|2�V ] �"2!;~úH2�Z�VM2 ]e^ 2,�M2<+�+�-�� 'T]' Q)K ^ � '<] �P2uV ] úH2�Z3[ )\Z?« '<]H^ 22�?V�-0� +.2�Ä}�b2 ] -�V ' �p+ ^ �b2<4!����V ] ��)T[R�?Z�VM-�2<+F<ñ%�V��\�|Z02<+2GQ<cJ 'T] 4uG²<MQ�(�+3�b)@�' QT`K�4!2 ^ Z�2 ' +.2uV ] «�2 '<] Z�2<+túH) ] +32u-�V�«�25+t[ )PZ5�m�|aTc,J ^ ) ] Mó�P�|Z ' -0V�) ] + �?V�-0� ' « ' ;�V�«��&« ^ )�«"« '<] 4Ä,�|2��|22��2 ] �P-���)T[�Q!9��?�b2 ] -��|2?�|)w+3-0/ üH' +32<4�+ ^ �b2<4!����2�Z ^ � '<] �P2<+�[ Z�)�«�+32#Ä}�|2 ] -�V ' �b+ ^ �|2<4����MV ] �u)T[�Z02 ' 4Z02#Ä}�|25+3-�+-�) ^ ) ]e^�' -�2 ]H' -�VM) ] )T[�+32�Ä,�|2 ] -0V ' �pZ�2 ' 4b+F<

%|)PZ ü )\-0� 9�1�ý*/ üH' +32<4 '<] 4�[ ������/B� ] ))�2�M2543�P2�+ ^ �|254!���MV ] �|O,V�-�VW+ ü 2 ] 2FM ^ V ' �H-0)r+32�Ä,�|2 ] -0V ' �/��Oz+ ^ �|2<4!/����2�Z02 ' 4�Z�2�Ä,�|2<+3-L+ ' -u-0�b2�4!VW+���[ )\Zu4�V�+3-�Z0V ü �|-0254�+ ^ �|2<4����MV ] ��)<[8-0�b2"4!V�+P��Z�2�Ä,�|2<+3-?-�Z '\^ 2<+F<g%|�|Z0-��|2�Z0/«�)\Z02,O<+.2�Ä}�b2 ] -�V ' �,+ ^ �|2<4����MV ] �?)T[��?Z�VM-�2�Z�2�Ä,�|2<+3-L+�+3)$«�2�-0V/«�2<+3ú|Z�)@:�V�4�2<+ ' úH2�Z.[ )PZo« 'T]H^ 2�V/«�ú|Z�)@:,2T«�2 ] -�?�|2 ] �e+3V ] �,+R4!VW+��b+f�?VM-��>%|����� ^ )$«"« '<] 4[Ä}�|2#�|2�V ] ��<�û�b2�Z02l[ )\Z02,O ' �/�!Z�2!« ' V ] V ] �*2T;~úH2�Z�V�«�2 ] -�+HV ] -0�|VW+^ � ' ú|-�2�Z?�H+.V ] ��-��|2�³uX '<] 4e��q6�-�Z '\^ 2<+?+3-��H43O 4�V�+���/ üH' +.2<4�+ ^ �|254!���MV ] � ' ���\)PZ0V�-0��«�+[�?VM-���+32�Ä,�|2 ] /-0V ' �8+ ^ �b2<4!����V ] ��)<[?Z�2 ' 4|+�<"���/��2T;~úH2�Z�V�«�2 ] -�+ «�)�4!2!�MV ] � 4!VW+��b+��?VM-0�°%|���/� ^ )$«"« 'T] 4zÄ,�|2��|2�V ] ���H+.2+32#Ä}�|2 ] -�V ' ��+ ^ �|2<4!�&�MV ] ��)T[r�?Z0VM-�2<+ ' +2�2T����<

�¶»!�B> �¤þB� vz�H�m�-»|���d��þBC�þ�C��C���@|�<�%�V��\�|Z025+�G²<MQT7UI�G²<D�$`�+3�b)@�L«�2 'T] Z02<+ úo) ] +32�-0V�«�2<+~[ )\Zz4!V�+.-0Z0V ü �|-�2<4�+ ^ �|2<4!�&�M2�ZuV/«�ú���2!«�2 ] - ' -�VM) ] +

�?VM-���« ' ;�V�«"��« ^ )$«"« 'T] 4,Ä,�|2��|25�M2 ] �P-0�e+�)<[R(|OEQ!9!O 'T] 4�Q!�� N< ª�)\Z02�)T[ -�2 ] -�� 'T]�] )P-#O ' « ' ;�V�«���«^ )$«"« 'T] 4�Ä,�|2��b2 �M2 ] �P-���)T[�Q!9uZ025+3����-�+�V ] «�2 '<] Z�2<+túH) ] +32?-0V/«�2<+p-�� ' - ' Z�2 ü 2�-0-�2�Z�)\Z8Z0)P�&�P���/O�2�Ä,�|V�:�/' ��2 ] --0)"-0�b),+32u[ )\Z ^ ) ] M��\�|Z ' -0VM) ] +2�?VM-0�\« ' ;!V/«��&«�Ä,�|2��b2���2 ] �\-0�H+)<[W(")PZ�QT�� 3<~ª�),+3-?2T; ^ 2Uú|-0V�) ] +-0)z-0�|VW+[�\2 ] 2�Z ' �MV/} ' -�VM) ] ' Z�2uV ] -0�|Z�2�2 ' Z02 ' +F<�%�V�Z�+3-#O ' « ' ;�V�«"��« ^ )$«"« '<] 4�Ä}�b2��|2���2 ] �P-���)T[R(sú|Z0)\/:�V�4!2<+�#!IN9Kµ�M))��2�ZW«�2 '<] Z02<+ úH) ] +.2�-�V�«�25+�[ )\Z?+ ^ �|2<4����MV ] � IJ�K�K:N �?V�-0�A%|����� ^ )�«"« '<] 4�Ä,�|2��|2�V ] � ÷(' +^ )$«�ú ' Z�2<4�-�) ' « ' ;!V/«��&« ��2 ] �P-���)<[RQT9�øÿ< �,2 ^ ) ] 4pOT[ )\Z �En�gMi È=� 'T] 4�q2l�s!J�l�O ' « ' ;!V/«���« ^ )�«"« '<] 4Ä,�|2��|2���2 ] �\-0� )T[~Q!�$ ^ú|Z�)):!VW4!2<+��oú�-�)"7N<D9QK ��)@��2�Z «�2 'T] Z�2<+túH) ] +32z-0V�«�2<+�[ )PZ�+3)$«�2 ^ ) ] M��\�|Z ' -0VM) ] +)T[t4!V�+P�!/ üH' +32<4�68/(9fV,Vg0�+ ^ �b2<4!����V ] �&<�û�bVMZ�4 'T] 4�«�),+.-8V�«�úH)PZ�- '<] -#O ' « ' ;�V�«"��« ^ )$«"« '<] 4,Ä,�|2��|2�M2 ] �P-���)<[8Q!9uVW+�V/����/ ' 43:!VW+32<4�[ )\Z�4!V�+.-0Z0V ü �|-�2<4�+ ^ �|2<4!�&�MV ] �u)T[�-0�|2,�uJ�kbNQl�vQ�)PZo�3��) ' 4��H+.V ] �r9�1�ý*/ üH' +.2<4+ ^ �|2<4����MV ] ��) ] 4!V�+P�|+��?VM-�� XRZ02<+.2�2!� ^ )$«"« 'T] 4�Ä}�|2#�|2�V ] ��<Wª ' ;!V/«��&« ^ )�«"« '<] 4�Ä,�|2��|2���2 ] �\-0�H+8)T[2�V�-0�|2�Z_(�)\Z�Q!�$ Vú|Z0)):�V�4!2g«�� ^ � ü 2#-0-02#Z�úo2#Z3[ )PZo« 'T]e^ 2*[ )PZ�-0�b2<+32 ^ ) ] M��P�bZ ' -�VM) ] +F<

�u+[�m�baTc,J ü 2 ] 2FMe-�+W«�)PZ�2�[ Z�)�« ^ ) ]H^�' -�2 ]H' -0VM) ] )T[t+32�Ä,�|2 ] -0V ' ��Z02 ' 4�Z�2�Ä}�b2<+3-L+�-0� '<] [ Z�)�«�+32�Ä,�|2 ] /-0V ' �E+ ^ �|2<4����MV ] ��)T[�Z02 ' 4|+lOQM��P�|Z�2EGQ<c�!Qh+3�|))��+,úH2�Z3[ )\Z?« '<]H^ 2h4 ' - ' [ )\Z�4!V�+.-0Z0V ü �|-�2<4�V/«�ú���2!«�2 ] - ' -�VM) ] +�H+.V ] �m68/;9fV,Vg0Z<y6��¶<:6=ù 'T] 4 ����û2%_<y6��¶<y6=ù ' -�-��|2��|)w+3-T<�68)$«�ú ' Z02<4-�?VM-0�4M��\�|Z024G²<MQT9!O-��|2«�2 '<] Z02<+ úH) ] +.2�-�V�«�25+�[ )PZ ^ ) ] Mó�P�|Z ' -0V�) ] +E�?V�-0�°« ' ;�V�«"��« ^ )�«"« '<] 4±Ä,�|2��|2>�M2 ] �P-0�e+�)<[5(�4!Z�)lúü O ' úoú|Z0));�V�« ' -02!�/O\#�`QK"<>�u+ ' Z�2<+3����-�Op-��|2Z«�2 '<] Z�2<+túH) ] +32"-0V�«�2<+~[ )\Z�-0�|2<+.2 ^ ) ] M��P�|Z ' -�VM) ] + ] ))�)P�b-púH2�Z3[ )\Z?«�-0�|)w+32��H+.V ] ��« ' ;�V�«"��«�Ä,�|2��|2g�M2 ] �\-0�H+8)T[�QT9 'T] 4�QT�� N<,û���H+lO ü )P-0��IJ�K�K:N '<] 4'�m�|aTcwJ' Z�2 ü 2<+3-8+.2�Z?:,254 ü O�4�V�+3-�Z0V ü �|-0254�+ ^ �|2<4!����2�Z�V�«{ú��M2!«"2 ] - ' -0VM) ] +o-�� ' - ' ���M))� -��|2?�|)w+3-0/ üH' +32<4"+ ^ �|2<4!�&�M2�Z-0) ^ ) ]H^�' -02 ]e' -02 ' +6« '<] O�Z�2�Ä,�|2<+3-L+ ' +,úH),+�+3V ü �M2,O��?�bV��M2 ' ����))�?V ] � ' +P« ' �/� ' «�)P� ] -�)T[�V ] -02�Z�/�Z�2�Ä}�b2<+3-^ ) ]H^ �|Z�Z02 ]H^ O ' -"2 'P^ ��4�V�+��m<�û�|274 ' - ' V ] - 'wü ��2H93<�Q�+.�3ú3úH)PZ�-�+�-��|V�+�) ü +32�Zo: ' -0V�) ]�¡ +32 ^ -�VM) ] 93<�Q�<�Q+3�b)@��+?-0� ' -h9�1�ý*/ üe' +3254�+ ^ �b2<4!����V ] � ' -�-0�|2��|)w+3- ' ��� ' O|+)\�|-púH2�Z.[ )PZ?«�+?9�1�ý*/ üe' +3254�+ ^ �b2<4!����V ] � ' --0�b2�4�V�+��"[ )PZ"IJ�K�K:N 'T] 4H�m�|aTc,J]<

vz�H�m¢f»|A<>bw��H�d�|£h��>bwl�<A<>b¼�þ��<C��d��¤<�BC!��þf½ > ��@ ¥A½�@H�HA<>`�<�B�-w� ^ Z�),+0+ ' �/��+3V/;���)PZo�3��) ' 4b+lO<-0�|2~4!Vi^E2�Z�2 ]H^ 2RV ] úH2�Z.[ )PZ?« 'T]H^ 2�4!�|2-�)u+P�?VM- ^ �|V ] � ü 2�-P�2�2 ] 68/(9fV,Vg0

'T] 4C����û2%x�|)w+3-�/ üH' +32<4"+ ^ �|2<4����M2�ZL+R4!2 ^ Z02 ' +32<+f�?V�-0��-��|22« ' ;�V�«"��« ^ )�«A« 'T] 4[Ä,�|2��|22��2 ] �\-0��<ñ%e)\Z '

Page 172: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q!7$J

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

20

40

60

80

100

120

140

160

Mea

n R

espo

nse

Tim

e (m

s)

ª CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

20

40

60

80

100

120

140

160

Mea

n R

espo

nse

Tim

e (m

s)

ª CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<C�¶pD F|·EG�IJ�KMK{NPO�Q\¸y¹<º<S�UH»*VW+3-0Z�V ² �b-02<4�¼ ^ �|2<4!�b´MV ]b±�½ ´ ± )PZ�VM-���«¾X�2�Z.[ )PZo« 'T]H^ 2

Page 173: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\À

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<Cx¶ED F�ÁtG?ÂEÃ|aTcwJ�ORQP¸ÅÄPº<S�UH»*V�+.-0Z�V ² �|-�2<4�¼ ^ �|2<4!�|´�V ]|±r½ ´ ± )PZ�VM-0�&«�X�2#Z3[ )PZo« 'T]e^ 2

Page 174: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿�Q

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?>�@HµBA<Cx¶ED�F|¶EG*fhg l�i�Æ�Ç#klOHÄ!¸ÅºTS�Ub»*V�+.-0Z0V ² �|-�2<4�¼ ^ �b2<4!�|´�V ]|±r½ ´ ± )PZ0V�-0��«ÈX�2�Z3[ )\Z?« '<]H^ 2

Page 175: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\Ä

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

25

30

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

25

30

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<C�¶pD F�É�G*ÂEn�gMi ÈpÂeOpÄ�¸ÊºTSrUH»*V�+.-0Z0V ² �|-�2<4�¼ ^ �|2<4!�b´MV ]b±"½ ´ ± )PZ0V�-0��«ËX�2�Z.[ )PZo« 'T]H^ 2

Page 176: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\Ì

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<C�¶pD FN­�G�q2l0s!JtljOEQP¸ÊÀ<S�UH»*VW+3-0Z�V ² �b-02<4�¼ ^ �|2<4!�b´MV ]b±�½ ´ ± )PZ�VM-���«�XB2�Z3[ )\Z?« '<]H^ 2

Page 177: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿<Í

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

20

40

60

80

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?>�@HµBATC�¶ED`_&¯�G*ÆuJ1k|NQl�v OpQP¸ÅÀTS�Ub»*V�+.-0Z�V ² �|-�2<4�¼ ^ �|2<4!�|´�V ]|±r½ ´ ± )PZ�VM-0�&«¾X�2�Z.[ )PZ?« 'T]H^ 2

Page 178: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\º

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.CR (Host)« SSTF.CW.CR¬

­;',® XRZ025+32�2�¯ 68)�«A« 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.CR (Host)« SSTF.CW.CR¬

­ ²p®�³ �|´M´R68)$«"« 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<Cx¶ED�_EFoG?ÂEÃ|aTcwJ�ORQP¸ÅÄPº<S�UH»*V�+.-0Z�V ² �|-�2<4�¼ ^ �|2<4!�|´�V ]|±r½ ´ ± )PZ�VM-0�&«�X�2#Z3[ )PZo« 'T]e^ 2

Page 179: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\¿

« '<Î V/«���«�Ï}�|2#�|2?´M2 ]b± -0�")T[�Q#¿!O�-0�|2 ^ � 'T]b± 2uV ] «�2 'T] Z025+3ÐH) ] +.2*-�V�«�2?Z ' Z�2�´MÑz2 Î|^ 2�2<4|+Q<ÒÓ[ )PZ�Ô)PZ�¯!/´M) ' 4|+?)P-��|2�Z�-0� '<] IJ�KMK{NP¸*Õ�b2E«�)w+3- ] )\-0V ^ 2 'T² ´�2�2 Î|^ 2�Ð|-0V�) ] VW+�-��|2z¿}Ò�ÐH2�Z3[ )\Z?« '<]H^ 2 ' 4�Ö '<] - 'T± 2�)T[�|)w+3-0/ ²H' +32<4�68/(9�×�×hØÙ)<Ö,2�ZR�|)w+3-0/ ²H' +32<4�¼b¼�Õ ³ Ô?�b2 ] + ^ �|2<4!�b´MV ]b± ÆuJ�kbNQl�v,�H+3V ]|± 4!V�+.¯|+�Ô?V�-0��XRZ02<+.2�2�¯^ )$«"« 'T] 4�Ï,�|2��|2�V ]|± ¸ ³ )PZ ' « 'TÎ V�«��&«ÚÏ,�|2��b2*´�2 ]|± -���)<[�Q�Ä\Û!O!-��|2 ^ �|)\V ^ 2�)T[��|),+.-0/ ²H' +.2<4 + ^ �|2<4!�b´M2�Z'5Ü 2 ^ -�+�«�2 'T] Z02<+.ÐH) ] +.2�-0V/«�2<+ ² ÑmQTÒÝ)PZz´M2<+�+l¸\Ô ] -�2�Z?«�+*)T[�V ] 4!VMÖ�V�4�� ' ´8Ô)\Z0¯�´M) ' 4|+ÞO�IJ�KMK:N�V�+u-��|2«�)w+3-�+32 ] +.VM-�VMÖ,2-�)�-0�|2��|),+.-0/ ²H' +.2<4�+ ^ �|2<4��|´MV ]|±u' ´ ± )PZ0V�-0��«7¸ ³ )\Z[«�),+3- ^ ) ]!ßH± �bZ ' -�VM) ] +lO ' 4!� ' ´t¼b¼�Õ ³+ ^ �|2<4��|´M2�Z�V/«�Ð|´M2T«�2 ] - ' -�VM) ] ÐbZ0)<Ö!VW4!2<+u-0�b2�´M)<Ô25+3- ­ )\Z�2<Ï}�bVMÖ ' ´�2 ] - ® «�2 '<] Z�2<+3ÐH) ] +32 -0V/«�2<+ ' «�) ]b±-0�b2�9�1?à�/ ²H' +32<4 ' ´ ± )PZ�VM-���« +�Ô?�b2 ] + ^ �|2<4!�|´�V ]|± -��|2�IJ�KMK{Nr-�Z '\^ 2,¸

Õ�|2 ^ �|)PV ^ 2 ² 2#-3Ô�2�2 ] 68/(9�×�×hØ '<] 4�¼|¼�Õ ³ [ )\ZR4�V�+3¯�/ ²H' +.2<4�+ ^ �|2<4!�b´MV ]b± VW+tÔ�)PZ0¯�´M) ' 4�4!2#Ðo2 ] 4!2 ] -�¸68/(9�×�×hØ ± 2 ] 2�Z ' ´�´MÑ�Ð|Z0)<Ö�V�4!25+�´M)<Ô2#Zf«�2 'T] Z�2<+3ÐH) ] +32�-0V/«�2<+p[ )PZÂEn#gMi Èp 'T] 4�q2l�s!J�l�OTÔ?�|2#Z02 ' +~¼b¼�Õ ³± 2 ] 2�Z ' ´M´�Ñ�Ð|Z�)TÖ�V�4�2<+R´M)<Ô2�Zñ«�2 'T] Z�2<+3ÐH) ] +32u-�V�«�25+�[ )\Z�IJLKMK:N 'T] 4 fhg lji�Æ�Ç#kl¸8¼|¼�Õ ³ ' ´�+3)�)\�|-0ÐH2�Z.[ )PZ?«�+68/(9�×�×hØÙ[ )PZ�ÂEÃ|aTc,J '<] 4�ÆhJ�kbNQljv�Ô?�|2 ] �e+3V ]b± XRZ�2<+32�2#¯ ^ )�«"« 'T] 4zÏ}�|2#�|2�V ]b± ¸RÕ�bV�+ ² 2�� ' Ö!V�)PZ~4!2�Ö�VM/' -�2<+t[ Z�)�«Ú-�� ' -�)T[ ^ 2 ] -0Z ' ´MV�á�2<4�+ ^ �|2<4��|´MV ]|± O<Ô?�|2�Z�2*68/(9�×�×hØÙ)\�|-0ÐH2�Z.[ )PZo« +�¼b¼�Õ ³ [ )PZ ' ´M´�Ô)\Z0¯�´M) ' 4|+2 Îb^ 2�Ð|-�IJ�KMK:NP¸?¼,V ]H^ 2�-0�|2h+32<Ï,�|2 ] -0V ' ´H+.-0Z�2 ' «â)\Ð|-0V/«�VMá ' -0V�) ] +�V/«�Ð|Z�)TÖ,2�¼|¼�Õ ³ «�)PZ02?-�� 'T] 68/;9�×�×hØ�OVM-zV�+ ] )\-"+3�|Z�Ð|Z0VW+3V ]|± -0� ' -�-0�|2 -.Ô) ' ´ ± )PZ0V�-0��«�+�ÐH2�Z3[ )\Z?«ã2<Ï,� ' ´�´MÑ�Ô?VM-0�m-.Ô)�´M2�Ö,2#´�+u)T[�+32<Ï,�|2 ] -0V ' ´+3-�Z02 ' «â)PÐ|-�V�«�V�á ' -�VM) ] +�V ] Ð|´ 'P^ 2,¸�Õ� ' -�V�+ÞO}Ô?V�-0� ¼|¼�Õ ³ +.2�Z0Ö�V ^ V ]|± +.2<Ï,�|2 ] -0V ' ´|Z025Ï}�|25+3-�+RV ]"' « '<]|] 2�Z+3V/«�VM´ ' ZR-�)�-�� ' -�)T[�68/;9�×�×hØ�O!-0�b2�+3�|)\Z0-�2�Z «�2 'T] +32�2�¯�-�V�«�25+�V ]H^ �|Z0Z�2<4 ² Ñ�¼|¼�Õ ³ [ Z�2<Ï}�b2 ] -�´MÑzZ02<+.�|´M-V ] +.�|ÐH2�Z0V�)PZ5«�2 'T] Z02<+.Ðo) ] +32z-0V/«�2<+l¸

³ )PZ�4!V�+.-0Z�V ² �|-�2<4"+ ^ �|2<4!�|´�V ]|± )T[�-��|2h4!V�+.¯�Z025Ï}�|25+3-R-�Z 'P^ 2<+lO|¼�X8Õ ³ / ²H' +.2<4 ' ´ ± )\Z0V�-0��« +R)\�|-0ÐH2�Z.[ )PZ?«9�1?à*/ ²H' +.2<4 ' ´ ± )PZ�VM-0�&« + ' - -��|2�4!V�+.¯p¸ ½ +�Ô ' +�-0Z0�b2x[ )\Z ^ 2 ] -0Z ' ´MV�á�2<4�+ ^ �|2<4!�|´�V ]|± O ' 4|4!V ]|±�'T± 2�/+32 ] +3V�-0VMÖ�VM-.Ñ"-0) ¼�X6�Õ ³ V�«�ÐbZ0)<Ö,2<+�)\Zu4�2 ± Z ' 4!2<+�Ðo2#Z3[ )PZo« 'T]e^ 2�4!2�ÐH2 ] 4!V ]|± ) ] -��|2�Ô�)PZ�¯!´�) ' 4E¸�³�)TÔ?/2�Ö,2�Z#O|-0�|2 '<² +3)\´M�|-�2 ^ � '<]|± 2zV ] «�2 '<] Z02<+.Ðo) ] +32�-�V�«�2hV�+?Z ' Z�2�´MÑ ± Z02 ' -02#Z*-�� 'T] Q�ä�Ä}Ò�¸u¼,2 ^ -�VM) ] ¹,¸ÅÄ!¸�Q^ )$«�Ð ' Z�2<+�-��|2z+3- ' Z0Ö ' -0VM) ] Z02<+.V�+.- 'T]e^ 2�)T[�-0�|2�Ö ' Z�VM)P�e+*4!VW+3-�Z0V ² �|-02<4 + ^ �|254!�|´M2#ZV�«�Ð|´M2!«"2 ] - ' -0V�) ] + ­(' +«�2 ' +3�|Z�2<4 ² Ñ�-0�b2�+�Ï}� ' Z0254 ^ ),2lå ^ VM2 ] -�+8)T[8Z�2<+3ÐH) ] +32�-�VMæ�2�Ö ' Z�V ' -�VM) ]p® ¸

çz�H�m¢f»|A<> è��H�Yé">��<�ÙçzC��o�<A)»�½ >�ê,C�����¤<��C��Bµf½ >��B@Õ '<² ´M2�¹w¸MQ�+3�b)TÔ�+?ÐH2�Z3[ )\Z0æ '<]H^ 2h4 ' - ' [ )\Z?-0�|2�ë ² 2<+3-Lì�9�1?à�/ ²H' +32<4 ^ 2 ] -0Z ' ´MV�á�2<4 '<] 4�4!VW+3-�Z0V ² �|-02<4

+ ^ �|2<4��|´M2�Z�VMæ�Ð|´M2�æ"2 ] - ' -0V�) ] +�[ Z�)PæÝ-0�|2�2 Î ÐH2�Z0V�æ�2 ] -�+ ^ )<Ö,2�Z�2<4 ² Ñ�-0�|VW+u4!VW+0+32#Z0- ' -0V�) ] ¸ ³ )PZ ^ ) ]!ßH± �|/Z ' -0V�) ] +�Ô?VM-0�íXRZ02<+.2�2�¯ ^ )\æ�æ '<] 4�Ï,�|2��|2#V ]|± O�4�V�+3-�Z0V ² �|-0254�+ ^ �|2<4!�|´�V ]|± � ' +��|Ð�-0)7Ì}ÒÝ�|V ± �|2�Z�ÐH2�Z0/[ )PZ�æ 'T]e^ 2�[ )PZ ' ´�´�+3V Î ³uX '<] 4d»hî~6�-0Z '\^ 2<+Þ¸ ï��|2 ]�³ �|´�´ ^ )\æ�æ '<] 4 Ï,�|2��|2�V ]|± VW+�2 ]H'<² ´M2<4EO�-��|24!VW+3-0Z�V ² �b-02<4 'T] 4 ^ 2 ] -0Z ' ´MV�á�2<4�VMæ�Ð|´�2�æ�2 ] - ' -�VM) ] +�ÐbZ0)<Ö!VW4!2�Z0)\� ± �|´�Ñ 2<Ï}�bVMÖ ' ´�2 ] -?ÐH2�Z.[ )PZ�æ 'T]H^ 2*[ )PZ ' ´M´Ô)\Z0¯�´M) ' 4|+�2 Îb^ 2�Ðb-�IJ�K�K:NPOÔ?�|2�Z�2�-0�b2��b),+3-�/ ²e' +3254 ^ 2 ] -0Z ' ´�VMá�2<4�+ ^ �|2<4��|´M2�Z�� ' + ' º,Òð´�)<Ô2�Zzæ�2 'T]Z025+3ÐH) ] +.2�-�VMæ�2,¸BÕ�|2#Z02l[ )\Z02,O�-0�|2 ^ �|)PV ^ 2u)T[ '�^ 2 ] -�Z ' ´�VMá�254�Ö,2�ZL+3�H+ ' 4�V�+3-�Z0V ² �|-0254�V�æ�Ð|´�2�æ�2 ] - ' -0V:) ] VW+] )\- ^ Z�� ^ V ' ´p-�) 'P^ �|VM2#Ö!V ]|±�± ),)�4�9�1?à*/ ²H' +32<4 + ^ �|2<4��|´M2�Z�ÐH2�Z3[ )\Z0æ '<]H^ 2,¸

Õ '<² ´M2�¹,¸ÊÄ +.�|)<Ô�+�Ðo2#Z3[ )PZ�æ 'T]e^ 2"4 ' - ' [ )\Z�-0�b2�ë ² 25+3-�ì ^ 2 ] -�Z ' ´MVMá#2<4 '<] 4 4!VW+3-0Z�V ² �b-02<4�+ ^ �|2<4!�b´M2�ZVMæ�Ð|´M2�æ"2 ] - ' -0V:) ] +u�H+.V ]|± -��|2�¼�X6�Õ ³ [ �|´�´M/ ¯ ] )<Ô?´�2<4 ± 2�+ ^ �|2<4!�|´�V ]|±7' ´ ± )PZ�VM-��|æ�¸ ³ )PZ"XRZ�2<+32�2#¯ 'T] 4³ �|´M´ ^ )\æ�æ 'T] 4�Ï}�b2��|2�V ]|±�^ ) ]!ßH± �|Z ' -0V�) ] +ÞO�4�V�+3-�Z0V ² �|-0254�+ ^ �|2<4��|´MV ]|± ÐbZ0)<Ö!VW4!2<+?2<Ï,�|VMÖ ' ´�2 ] -?)PZ�+.�|ÐH2�/Z0V�)PZzæ�2 'T] Z02<+.Ðo) ] +32 -�VMæ�2<+*[ )\Z ' ´M´~+3V Î 4!VW+3¯�Z02<Ï,�|2<+.-�-�Z 'P^ 2<+l¸ ³ )\Z�-��|2�ÂEÃ|aTc,Jz-0Z '\^ 2,O84!VW+3-�Z0V ² �|-02<4+ ^ �|2<4��|´M2�ZL+�Ð|Z0)�4�� ^ 2mQlÍ<äHQ#Û}Ò ´M)<Ô�2�Z�æ�2 'T] Z025+3ÐH) ] +.2�-0V�æ�2<+l¸ ³ )\Z ^ ) ]!ßH± �bZ ' -�VM) ] +�Ô?VM-0�ñXRZ02<+.2�2�¯^ )\æ�æ 'T] 4�Ï}�b2��|2�V ]|± OH4!VW+3-�Z0V ² �|-02<4 + ^ �|254!�|´MV ]|± )T[�-0�|2�³uXY-�Z 'P^ 2<+ ' ´�+.)�� ' + ' +3V ±\] V ßo^�'T] - ^ )Pæ�Ð|´�2 Î /VM-.Ñ ' 4!Ö '<] - 'T± 2w¸�Õ�|2 ² 2<+3- ^ 2 ] -0Z ' ´MV�á�2<4�´�) ^�' -�VM) ] [ )\Z�-��|2<+.2�-�Z '\^ 2<+�V�+�-0�b2��b),+3-#O 'T] 4Y�|)w+3-0/ ²H' +32<4¼�X6�Õ ³ + ^ �|2<4��|´MV ]|± Z�2<Ï,�|VMZ�2<+ ' +3V ±P] V ßE^�'<] -u2 Ü )\Z0- ¡�' ´�´R4!VW+3¯�/;+.ÐH2 ^ V ßo^ V ] [ )PZ0æ ' -0V�) ] Z02#´ ' -�2<4�-�) 4 ' - '´ ' Ñ,)\�|-�O<æ�2 ^ � 'T] V ^�' ´ 'T] 4�)TÖ,2#Z0�|2 ' 4�4!2#´ ' Ñ|+ÞO ^#'P^ �|2 ^ ) ] -�2 ] -�+lO 'T] 4 ^ �|Z0Z�2 ] -�Z�)P- ' -0V�) ]H' ´|ÐH),+3V�-0V�) ] æ"�H+3-² 2�2 Î -0Z 'P^ -�2<4 '<] 4�-0Z 'T] +;[ 2�Z0Z�2<4�-�)�-0�b2��|)w+3-0/ ²H' +32<4�+ ^ �|254!�|´M2#Z�¸ï�V�-0��4�V�+3-�Z0V ² �|-0254�+ ^ �|2<4��|´MV ]|± O|-��|2

Page 180: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿,¹

ÕtZ 'P^ 2 ³�),+3-u¼ ^ �|254 »*VW+3¯�¼ ^ �|254 ò�2 'T]�ó 2<+3м ^�' ´M2 ­;' ´�´R¸:68ï ® ­;' ´M´8¸:¼|¼ óu® 6?° ÕV�æ�2 ­ æ + ®682�´M´�) 682 ] -0Z ' ´ ¼|¼�Õ ³ ¸y¼|¼ ó Ä Q#ÌPÌ!¸�Q�ôQ\¸y¹5º »*VW+3-0Z�V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼b¼�Õ ³ Q�¿ FN®�¯�D�F�Á

¼ ]H' ¯,2 682 ] -0Z ' ´ 68/;9�×�×hØ�¸y6 ó Ä Ä\Ì!¸:¹<ºQ\¸ÊÄ\º »*VW+3-0Z�V ² 68/;9�×�×hØ�¸y6 ó 68/(9�×�×uØ Í Ä\Ì!¸Å¿PÛ

½ VMZ0/ ó +3Ö 682 ] -0Z ' ´ 68/(9�×�×uØ Q�Ä\Û Ä\ô!¸ÅºPÄÄ!¸Êº »*VW+3-0Z�V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼b¼�Õ ³ Q�¿ _|É�D�É�¾

¼ ^ VM/(Õ*¼ 682 ] -0Z ' ´ 68/;9�×�×hØ�¸y6 ó Ä Ä\À!¸Å¿PÌÄ!¸Êº »*VW+3-0Z�V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼b¼�Õ ³ Q�¿ _�¯�D�_EF

×�Z�4!2#Z 682 ] -0Z ' ´ 68/(9�×�×uØ Q�Ä\Û Ä\Ì!¸ÅÄP¿QP¸ÊÀ »*VW+3-0Z�V ² ¼|¼�Õ ³ ¸y¼|¼ ó 68/(9�×�×uØ Q�Ä\Û Ä\Ì!¸ÅÄPº

ó 2#Ðo)\Z0- 682 ] -0Z ' ´ 68/;9�×�×hØ�¸y6 ó Ä ÍwÀ!¸Åº!QQP¸ÊÀ »*VW+3-0Z�V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼b¼�Õ ³ Q�Ä\Û ®�­�D/®�®

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

Õ�Z '\^ 2 ³*),+.-u¼ ^ �|2<4 »*VW+3¯�¼ ^ �|254 ò�2 'T]7ó 2<+.м ^#' ´M2 ­;' ´M´�¸y68ï ® ­(' ´M´�¸y¼|¼wïõ¸y¼|¼ óu® 6?° ÕVMæ�2 ­ æ�+ ®682�´�´M) 682 ] -�Z ' ´ ¼|¼�Õ ³ ¸y¼|¼ ó Ä FN¯tFHD/­HÁQP¸:¹<º »�V�+3-�Z0V ² 68/(9�×�×uØ�¸:¼|¼ ó 68/(9�×�×uØ Í Q�À,¹,¸Ê¿\Ä

¼ ]H' ¯,2 682 ] -�Z ' ´ 68/(9�×�×uØ�¸:6 ó Ä ÄPÄ�¸Ê¿\ÛQP¸ÅÄPº »�V�+3-�Z0V ² 68/(9�×�×uØ�¸:6 ó 68/(9�×�×uØ Í _H_ED�®HÁ

½ VMZ�/ ó +3Ö 682 ] -�Z ' ´ ¼b¼�Õ ³ Q#ÄPÛ ÄPº�¸y¹5¿Ä!¸Åº »�V�+3-�Z0V ² 68/(9�×�×uØ�¸:¼|¼ ó ¼b¼�Õ ³ Q�¿ ÄPº�¸Ê¿\Ì

¼ ^ VM/(Õ*¼ 682 ] -�Z ' ´ 68/(9�×�×uØ Q#ÄPÛ Q�¿�¸y¹5ôÄ!¸Åº »�V�+3-�Z0V ² ¼|¼�Õ ³ ¸y¼|¼ ó 68/(9�×�×uØ Q#ÄPÛ Q�¿�¸y¹5¿

×�ZL4!2�Z 682 ] -�Z ' ´ 68/(9�×�×uØ Q#ÄPÛ Ä!Q\¸Ê¿\ÌQP¸ÅÀ »�V�+3-�Z0V ² 68/(9�×�×uØ�¸:¼|¼ ó 68/(9�×�×uØ Q#ÄPÛ Ä!Q\¸Ê¿\Ì

ó 2�ÐH)PZ�- 682 ] -�Z ' ´ 68/(9�×�×uØ Q#ÄPÛ ÌPÌ�¸ÊÌ\ºQP¸ÅÀ »�V�+3-�Z0V ² 68/(9�×�×uØ�¸:¼|¼ ó 68/(9�×�×uØ Q#ÄPÛ ÌPÌ�¸ÊÌ\º

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

º »&¼f½ C�¶ED�FHG�ò�2 'T]7ó 2<+.ÐH) ] +.2�ÕV�æ�2<+R[ )PZ"ë ó 2 ' +.) ]H'<² ´M2<ì"9�1?à*/(1 ' +.2<4�¼ ^ �b2<4!�|´�2�Z�+

Page 181: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\Û

ÕtZ 'P^ 2 ³*),+.-�¼ ^ �|254 »*VW+3¯�¼ ^ �|254 ò�2 'T]�ó 2<+3м ^#' ´M2 ­;' ´M´8¸:68ï ® 6?° ÕV�æ�2 ­ æ�+ ®682�´�´M) 682 ] -�Z ' ´ ¼}X~6�Õ ³ ¸y6 ó Q Q\Q�¿!¸:¹<ÄQP¸:¹<º »�V�+3-�Z0V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�¿ FHFN¾�D�FN®

¼ ]H' ¯,2 682 ] -�Z ' ´ ¼}X~6�Õ ³ ¸y6 ó Q Ä\¿!¸ÅôTÍQP¸ÅÄPº »�V�+3-�Z0V ² 68/(9�×�×uØ�¸:6 ó ¼�X6�Õ ³ ¸:¼|¼ ó Í _o_ED�¶H·

½ VMZ�/ ó +3Ö 682 ] -�Z ' ´ ¼}X~6�Õ ³ Q�Ä\Û Ä<Í|¸ÅºPÄÄ!¸Åº »�V�+3-�Z0V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�¿ _�®�D/­�­

¼ ^ VM/(Õ*¼ 682 ] -�Z ' ´ ¼}X~6�Õ ³ Q�Ä\Û Q#Û!¸:¹<ôÄ!¸Åº »�V�+3-�Z0V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�¿ Fe¶ED/¾�¯

×�ZL4!2�Z 682 ] -�Z ' ´ ¼}X~6�Õ ³ Q�Ä\Û Ä\À!¸�QPQQP¸ÅÀ »�V�+3-�Z0V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�Ä\Û Ä\À!¸�Q�º

ó 2�ÐH)PZ�- 682 ] -�Z ' ´ ¼}X~6�Õ ³ Q�Ä\Û Ì\À!¸�Q�¿QP¸ÅÀ »�V�+3-�Z0V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�Ä\Û Ì\À!¸�QlÍ

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

Õ�Z '\^ 2 ³�),+3-�¼ ^ �|2<4 »*VW+3¯�¼ ^ �|254 ò�2 'T]�ó 25+3м ^�' ´�2 ­;' ´�´8¸y68ï ® 6?° ÕVMæ�2 ­ æ + ®682#´M´M) 682 ] -�Z ' ´ ¼�X6�Õ ³ Q�ÄPÛ Q�ÀPô�¸öÍwºQP¸:¹<º »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸:¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Í F3¯p·ED/¾oÉ

¼ ]H' ¯,2 682 ] -�Z ' ´ ¼�X6�Õ ³ Q�ÄPÛ ÄPº�¸MQPQQP¸ÅÄPº »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸:6 ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Í _EFHDMÁp_

½ V�Z0/ ó +.Ö 682 ] -�Z ' ´ ¼�X6�Õ ³ Q�ÄPÛ Ä!Q\¸ÊÌPÀÄ�¸Êº »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸:¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q#¿ Ä!Q\¸ÊÌPº

¼ ^ V�/;Õ*¼ 682 ] -�Z ' ´ ¼�X6�Õ ³ Q�ÄPÛ Q�Ì�¸öÍ,ôÄ�¸Êº »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ Q�Ì�¸öÍ,º

×*ZL4!2�Z 682 ] -�Z ' ´ ¼�X6�Õ ³ Q�ÄPÛ Q�Û�¸ÊÌPºQ\¸ÊÀ »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:68ïõ¸y¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ Q�Û�¸öÍ,À

ó 2�ÐH)PZ�- 682 ] -�Z ' ´ ¼�X6�Õ ³ Q�ÄPÛ ÄTÍb¸Êº!QQ\¸ÊÀ »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:68ïõ¸y¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ ÄTÍb¸ÊºPÀ

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

º »�¼R½�C�¶ED�_EG?ò�2 'T]�ó 2<+3ÐH) ] +32rÕVMæ�2<+�[ )\Z�ë ó 2 ' +3) ]H'T² ´�2<ì�¼�X6�Õ ³ ¼ ^ �|2<4!�b´M2�ZL+

Page 182: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�¿\ô

[ �|´�´M/ ¯ ] )<Ô?´�2<4 ± 2z+ ^ �|254!�|´M2#Z?Z02<+.V�4!2<+ ' -h-0�|2r4!V�+.¯ ­ Ô?V�-0� [ �|´M´ '\^�^ 2<+�+*-0)�-��|2 ] 2 ^ 2<+�+ ' Z�Ñ ^ ) ]!ße± �|Z ' -0V�) ]'T] 4�+3- ' -�2�V ] [ )PZ�æ ' -�VM) ]p® ¸

� À�� À�Á ÷�Ä5ÑPÑ Ã_Ê5Ò!ø|�WÅ ù>É�Ç�Ð��RÒ³ )PZB´MV ± �!-BÔ)\Z0¯�´M) ' 4|+ÞO,4!V�+.-0Z�V ² �|-�2<4�+ ^ �|2<4!�b´M2�Z�V�æ�Ð|´M2#æ�2 ] - ' -�VM) ] +oÐ|Z�)TÖ�V�4�2�-��|2?+ ' æ�28ÐH2�Z.[ )PZ0æ 'T]H^ 2

' +z4!V�+.¯!/ ²H' +32<4 ^ 2 ] -0Z ' ´MV�á�2<4�+ ^ �|2<4!�|´�2�Z�+ÞOB+3V ]e^ 2 ' ´�´�ÐH2 ] 4!V ]|± Z�2<Ï}�b2<+3-L+�-.Ñ�Ð|V ^#' ´M´�Ñ ß -�Ô?VM-0�bV ] -0�b2�) ] /² ) ' Z�4 ^ )\æ�æ 'T] 4�Ï}�b2��|2<+Þ¸ ½ +-0�b2�Ô)\Z0¯�´M) ' 4�V ] -�2 ] +.VM-.Ñ�V ]e^ Z02 ' +32<+ÞO|) ] / ² ) ' Z�4�Ï}�|2#�|2<+) ^�^�' +3V�) ]H' ´M´MÑZ02 'P^ ��-0�b2�VMZ?æ '<Î V�æ��bæâ´M2 ]|± -0�H+ 'T] 4�-0�|2��|)w+3-�/ ²H' +32<4�+ ^ �b2<4!�|´�2�Z�+ ² 2 ± V ] -0)�- ' ¯,2 'T]7'P^ -�VMÖ,2�Z0)\´M2�V ])PZL4!2�Z�V ]|± Z�2<Ï}�b2<+3-L+l¸

³ V ± �|Z025+�¹w¸ÊÄPÄ 'T] 4�¹,¸ÊÄ\Ì�Ð|Z�2<+32 ] -"æ�2 'T] Z�2<+3ÐH) ] +32�-�VMæ�25+ 'T] 4mæ�2 'T]m] ) ] / ^ )Pæ�Ðb�|-02�-0VMæ�2<+�[ )\Z-0�b2�ÛT/ �H+32�Z�ÂEú\Ã}ÆzûuJÞÃ�-0Z 'P^ 25+l¸üÕ�|2�ÐH2�Z.[ )PZ�æ 'T]H^ 2�VMæ�Ð 'P^ -�)<[�-��|2�æ 'TÎ VMæ"�|æ ^ )Pæ�æ 'T] 4mÏ,�|2��|2´M2 ]|± -��YÖ ' Z0VM25+�[ Z0)Pæ V�æ�Ð|´M2#æ�2 ] - ' -�VM) ] -0)�VMæ�Ð|´M2�æ"2 ] - ' -0V�) ] O ² �|-"-0�|2 ´�)TÔ�2<+3-zæ�2 '<]Y] ) ] / ^ )Pæ�Ð|�|-02-0V�æ�2<+�Z02<+.�|´M-"Ô?�|2 ] -0�|274!V�+.¯!/ ²H' +.2<4d+ ^ �b2<4!�|´�2�Z��H+325+ 'T] ¼|¼�Õ ³â' ´ ± )\Z0VM-��|æý[ )PZ�+ ^ �|2<4!�b´MV ]b± +3�|)\Z0-­ V(¸ö2,¸�O!Í"Z02<Ï,�|2<+.- ®�^ )\æ�æ '<] 4�Ï,�|2��b2<+l¸ ³ )PZh4!V�+.¯|+Ô?V�-0��XRZ�2<+32�2#¯ ^ )\æ�æ '<] 4�Ï,�|2��|2�V ]|± O ' �|)w+3-0/ ²H' +32<468/(9�×�×hØ�+ ^ �|2<4!�b´M2�Z?� ' + ' æ ' Z ± V ]H' ´�ÐH2�Z.[ )PZ0æ 'T]H^ 2 ' 4!Ö 'T] - 'T± 2,¸uï��|2 ]�³ �|´�´ ^ )Pæ�æ 'T] 4 Ï,�|2��|2#V ]|±V�+2 ]H'T² ´�2<4pO�VM-?� ' + ' æ ' Z ± V ]H' ´�4!V�+ ' 4!Ö 'T] - '<± 2,¸

³ V ± �|Z025+�¹,¸ÅÄTÍ '<] 4�¹,¸ÅÄPº�+.�|)<ÔÙæ�2 'T] Z025+3ÐH) ] +.2�-0VMæ�2<+ 'T] 4 ' Ð|Ð|´�V ^�' -0VM) ] Z0� ] -0V�æ�2<+t[ )\Z-0�b2 I8NQj�ikmljJ�Ç�ÇHÔ)PZ�¯!´�) ' 4p¸ ³ )PZ ^ ) ]!ßH± �|Z ' -0V�) ] +�Ô?VM-���XRZ�2<+32�2#¯ ^ )\æ�æ '<] 4*Ï,�|2��b2�V ]|± O�-0�|28æ '<Î V�æ��|æ ^ )Pæ�æ '<] 4Ï,�|2��|2�´M2 ]|± -�� '�Ü 2 ^ -�+�+3Ñb+3-�2�æ�/ ´M2�Ö,2#´oÐH2�Z.[ )PZ�æ 'T]H^ 2 ² Ñ�´M2<+�+-0� '<] QTÒ�¸Õ�|2�´�)TÔ�2<+3-?Z�� ] -�VMæ�25+�) ^�^ �bZÔ?VM-�� ' æ 'TÎ VMæ"�|æ ^ )\æ�æ '<] 4�Ï,�|2��|2�´M2 ]|± -���)T[hQ#¿ 'T] 4 ' 4!VW+3¯�/ ²H' +32<4�+ ^ �|2<4!�b´M2�Z?�H+.V ]|± ) ] 2z)T[8-��|2^�'\^ �|2#/;+.2 ] +3V�-0V�Ö,2�¼�X8Õ ³�' ´ ± )PZ�VM-0�bæ +l¸

çz�H�m¢�þ|A<> è��H�Yé">��<�ÙçzC��o�<A<þ|ÿ >�ê,C�����¤<��C��Bµ�ÿ >��B@Õ '<² ´M25+x¹,¸ÅÌ 'T] 4�¹w¸öÍ ' ´M´�)<Ô ^ )\æ�Ð ' Z�V�+.) ] ² 2#-3Ô�2�2 ] -��|2Ùë ² 2<+3-Lì ^ 2 ] -0Z ' ´�VMá�2<4 '<] 4Ó4!VW+3-�Z0V ² �|-02<4

+ ^ �|2<4��|´M2�ZL+l¸�Õ�|2*´�VMæ�V�-02<4 ^ )\æ�æ '<] 4�Ï,�|2��|2�´M2 ]|± -��H+RVMæ�ÐH),+.2<4�) ] -0�|2h4!V�+.¯!/ ²H' +32<4�+ ^ �b2<4!�|´�2�Z�+�æ ' ¯,2�|)w+3-0/ ²H' +32<4 ^ 2 ] -0Z ' ´�VMá�2<4�+ ^ �|2<4!�b´MV ]b± -0�|2 ² 2<+3- ^ �b)PV ^ 2�[ )PZ�+ ^ �|2<4!�b´M2�Z�V�æ�Ð|´�2�æ�2 ] - ' -0V�) ] +�Ô?VM-��|)P�b-+3Ñb+3-�2�æ�/ ´M2�Ö,2#´p¯ ] )<Ô?´M2<4 ± 2,¸��*),+.-0/ ²H' +.2<4�+ ^ �|2<4!�|´�2�Z�+�Ð|Z0)�4!� ^ 2��bÐ�-�)�Ä,Ò ² 2�-0-�2�ZuÐH2�Z3[ )\Z0æ '<]H^ 2�)<Ö,2�Z4!VW+3¯�/ ²H' +32<4�+ ^ �|2<4!�b´M2�ZL+�)PZ�4�V�+3-�Z0V ² �|-0254�+ ^ �b2<4!�|´�2�Z�+R[ )PZ�-0�|2�ÂEú\Ã}ÆzûuJÞà 'T] 4�I8NQj�kmljJ0Ç�Ç8Ô�)PZ0¯�´M) ' 4|+Þ¸

��� � ��� ����� ������������������ ��!#"$����!»*V�+.-0Z�V ² �|-�2<4�+ ^ �|254!�|´M2#Z�V�æ�Ð|´�2�æ�2 ] - ' -�VM) ] + ±,' V ] -0�b2�+ ' æ�2*ÐH2�Z.[ )PZ�æ 'T]H^ 2 ² 2 ] 2 ß -L+�[ Z�)PæË+32<Ï,�|2 ] /

-0V ' ´B+.-0Z02 ' æ�)\Ð|-0V�æ�VMá ' -0V�) ] + ' +?-0�|2�V�Z ^ 2 ] -0Z ' ´MV�á�2<4 ^ )P� ] -�2�Z0Ð ' Z0-L+l¸ ³ )\Z*V�æ�Ð|´�2�æ�2 ] - ' -0V:) ] +�Ô?V�-0� æ 'TÎ /VMæ"�|æ 4!VW+3¯ ^ )\æ�æ 'T] 4�Ï}�|2#�|2�´M2 ]b± -0�e+�)T[�Q#¿Y)\Z��|V ± �|2�Z#O*æ�2 'T] Z02<+.Ðo) ] +32í-0VMæ�2<+ ' Z02 ± 2 ] 2�Z ' ´�´MÑ� ]H'�Ü 2 ^ -0254 ² Ñ�-0�|2 ^ �|)PV ^ 2 ² 2�-.Ô2�2 ] 68/(9�×�×hØ '<] 4�¼b¼�Õ ³ �b),+3-�/ ²e' +3254Ù+ ^ �|254!�|´MV ]|±í' ´ ± )PZ�VM-0�bæ +l¸Õ�|2z)PÐ|-�VMæ ' ´�4!VW+3¯�/ ²H' +32<4�+ ^ �b2<4!�|´�V ]|±"' ´ ± )\Z0V�-0�|æ�VW+�Ô�)PZ�¯!´�) ' 4�4!2�ÐH2 ] 4�2 ] -#O ² �|-u4�V�+3-�Z0V ² �|-02547¼b¼�Õ ³+ ^ �|2<4��|´M2�ZL+ ' Z02�æ�)\Z02 ^ ´M)w+32�´�Ñ�æ ' - ^ �|2<4 Ô?VM-���4!V�+.-0Z0V ² �|-�2<4x68/(9�×�×uØË+ ^ �|2<4!�|´�2�Z�+?-0� 'T] V�+*-��|2 ^�' +.2[ )PZ ^ 2 ] -0Z ' ´�VMá�2<4í+ ^ �|2<4!�|´�V ]|± ¸ ³ �|´M´�/�¯ ] )<Ô?´M254 ± 2�4!VW+3-0Z�V ² �b-02<4�+ ^ �|2<4!�|´�2�Z�VMæ�Ð|´M2�æ"2 ] - ' -0V�) ] +�Ð|Z0)<Ö�V�4!2-0�b2�´�)TÔ�2<+3-hæ�2 'T] Z025+3ÐH) ] +.2�-�VMæ�25+ ­ Ô?�|2 ] -��|2�) ] / ² ) ' ZL4Y4 ' - '�^�'P^ �|2<+u� ' Ö,2�Ð|Z�2l[ 2�- ^ �|V ]|± ) ] Z02 ' 4�|V�-�+?4!VW+ 'T² ´M2<4 ® ¸

³ )PZ�æ�),+.- ^ ) ]!ße± �|Z ' -0V�) ] +ÞO ' æ 'TÎ VMæ"�|æ ^ )\æ�æ '<] 4�Ï,�|2��|2�´�2 ]|± -0��)T[�Q#¿�Ð|Z�)<Ö!VW4!2<+u-0�|2"´M)<Ô�2<+3-æ�2 '<] Z02<+.ÐH) ] +.2u-0V�æ�2<+l¸BÕ�|VW+R´M2 ] 4b+ ' 4|4!V�-0VM) ]H' ´E+.�|Ð|ÐH)PZ�--0)z-0�|2 ^ ´ ' VMæü-0� ' -�4!V�+.-0Z0V ² �|-�2<4�+ ^ �b2<4!�|´�V ]|±Ð|Z�)TÖ�V�4�2<+ ² 2#-0-02#Z�)<Ö,2�Z ' ´M´8ÐH2�Z3[ )\Z0æ '<]H^ 2,¸&%�[�-��|V�+�Ô2�Z�2 ] )\-�-0�|2 ^�' +.2,O�æ�)w+3- ^ ) ]!ße± �|Z ' -0V�) ] +�Ô�)P�|´W4

Page 183: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5À

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

50

100

150

200

250

300

350

Mea

n R

espo

nse

Tim

e (m

s)

ª CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;'}® ò�2 '<]�ó 2<+.Ðo) ] +32rÕVMæ�2

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

' CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p® ò�2 '<] à�) ] /.68)Pæ�Ðb�|-02zÕVMæ�2

=?>�@HµBA<Cx¶ED`_H_EG�ÂoúPÃ}ÆzûuJÞÃ!O8Û�(h+32�ZL+lU"»*V�+.-0Z�V ² �|-�2<4Y¼ ^ �|2<4��|´MV ]|±�½ ´ ± )\Z0VM-��|æãX�2�Z.[ )PZ�æ 'T]H^ 2�[ )\Z»�V�+3¯b+Ô?VM-���XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

Page 184: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹wQ

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

50

100

150

200

250

300

350

Mea

n R

espo

nse

Tim

e (m

s)

ª CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;'}® ò�2 '<]�ó 2<+.Ðo) ] +32rÕVMæ�2

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

100

200

300

400

500

Mea

n N

on-C

ompu

te T

ime

(ms)

' CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p® ò�2 '<] à�) ] /.68)Pæ�Ðb�|-02zÕVMæ�2

=?>�@HµBA<Cx¶ED`_*)�G�ÂoúPÃ}ÆzûuJÞÃ!O8Û�(h+32�ZL+lU"»*V�+.-0Z�V ² �|-�2<4Y¼ ^ �|2<4��|´MV ]|±�½ ´ ± )\Z0VM-��|æãX�2�Z.[ )PZ�æ 'T]H^ 2�[ )\Z»�V�+3¯b+Ô?VM-�� ³ �|´�´�68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

Page 185: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5Ä

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;'}® ò�2 '<]�ó 2<+.Ðo) ] +32rÕVMæ�2

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

50

100

150

200

250

App

licat

ion

Run

Tim

e (s

ec)

+ CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�½ Ð|Ðb´MV ^#' -0V�) ] ó � ] ÕVMæ�2

=?>�@HµBA<Cx¶ED`_*,�G�I8NQj�kml�J0Ç�ÇÞU�»*VW+3-�Z0V ² �|-02<4�¼ ^ �|2<4!�|´�V ]|±�½ ´ ± )\Z0V�-0�|æõXB2�Z3[ )\Z0æ '<]H^ 2R[ )PZ�»*V�+.¯|+�Ô?VM-��XRZ�2<+32�2#¯�68)Pæ�æ 'T] 4�°��|2��|2�V ]|±

Page 186: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5Ì

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

10

20

30

40

50

60

Mea

n R

espo

nse

Tim

e (m

s)

CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;'}® ò�2 '<]�ó 2<+.Ðo) ] +32rÕVMæ�2

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

50

100

150

200

250

App

licat

ion

Run

Tim

e (s

ec)

+ CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�½ Ð|Ðb´MV ^#' -0V�) ] ó � ] ÕVMæ�2

=?>�@HµBA<Cx¶ED`_H·EG�I8NQj�kml�J0Ç�ÇÞU�»*VW+3-�Z0V ² �|-02<4�¼ ^ �|2<4!�|´�V ]|±�½ ´ ± )\Z0V�-0�|æõXB2�Z3[ )\Z0æ '<]H^ 2R[ )PZ�»*V�+.¯|+�Ô?VM-��³ �|´�´�68)\æ�æ 'T] 4�°��|2��|2�V ]|±

Page 187: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹#Í

�*)w+3-u¼ ^ �|2<4 »*V�+.¯�¼ ^ �|2<4 ò�2#-0Z0V ^Õ�Z 'P^ 2 ­;' ´M´8¸:68ïõ¸y¼|¼ óu® 6?° - ' ´��|2ÛT/.(u+.2�Z 682 ] -0Z ' ´ 68/;9�×�×hØ Í )�¶*,�D0/�¶

¼,Ñ ]Hó1 2 ] »*VW+3-�Z0V ² 68/;9�×�×hØ ¼|¼�Õ ³ Í Ì}¹<Û�¸ÊÀ\¿682 ] -0Z ' ´ 68/;9�×�×hØ Ä F32�FHD�É�_68)Pæ�Ð|Z�2<+0+ »*VW+3-�Z0V ² 68/;9�×�×hØ 68/;9�×�×hØ Í Q�ôTÍb¸ÊÄ�Q

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

��),+3-u¼ ^ �|254 »*V�+.¯�¼ ^ �|2<4 ò�2�-�Z0V ^Õ�Z '\^ 2 ­(' ´�´8¸y68ïõ¸y¼b¼ ó�® ­(' ´M´8¸:¼|¼,ïõ¸:¼|¼ óu® 6?° - ' ´��|2Û</�(h+32�Z 682 ] -�Z ' ´ 68/(9�×�×hØ Í )p¶*/�D`¶EF

¼,Ñ ]Hó1 2 ] »*V�+.-0Z0V ² 68/(9�×�×hØ ¼|¼�Õ ³ Í Ì,¹,QP¸ÅÀPô682 ] -�Z ' ´ 68/(9�×�×hØ Ä F�24/�D5/p·68)Pæ�Ð|Z02<+�+ »*V�+.-0Z0V ² 68/(9�×�×hØ 68/;9�×�×hØ Q#ÄPÛ Q#ôPÀ!¸ÅôPº

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

6þ#7Bÿ Cx¶ED5)�G�ò�2 '<] à�) ] /.68)Pæ�Ðb�|-02�ÕV�æ�2<+ ­ æ + ® )\Z ½ Ð|Ðb´MV ^#' -0V�) ]�ó � ] ÕVMæ�25+ ­ +32 ^<® [ )\Z�ë ó 2 ' /+.) ]H'<² ´M2<ì"9�1?à*/(1 ' +.2<4�¼ ^ �b2<4!�|´�2�Z�+

Page 188: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5º

�*)w+3-u¼ ^ �|2<4 »*V�+.¯�¼ ^ �|2<4 ò�2#-0Z0V ^Õ�Z 'P^ 2 ­;' ´M´8¸:68ïõ¸y¼|¼ óu® 6?° - ' ´��|2ÛT/.(u+.2�Z 682 ] -0Z ' ´ ¼�X6�Õ ³ Q )�¶H¶ED�¶#,

¼,Ñ ]Hó1 2 ] »*VW+3-�Z0V ² ¼b¼�Õ ³ ¼�X6�Õ ³ Q�¿ ÌPÛTÍb¸ÊÄ\À682 ] -0Z ' ´ ¼�X6�Õ ³ Q F32�FHD�ÉoÁ68)Pæ�Ð|Z�2<+0+ »*VW+3-�Z0V ² ¼b¼�Õ ³ ¼�X6�Õ ³ Í Q�ôPÌ�¸MQ#º

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

��),+3-u¼ ^ �|254 »*V�+.¯�¼ ^ �|2<4 ò�2�-�Z0V ^Õ�Z '\^ 2 ­(' ´�´8¸y68ïõ¸y¼b¼ ó�® ­(' ´M´8¸:¼|¼,ïõ¸:¼|¼ óu® 6?° - ' ´��|2Û</�(h+32�Z 682 ] -�Z ' ´ ¼�X6�Õ ³ Q )p¶H¶ED`¶*,

¼,Ñ ]Hó1 2 ] »*V�+.-0Z0V ² 68/(9�×�×hØ ¼�X6�Õ ³ Í Ì\Û!QP¸:¹<Û682 ] -�Z ' ´ ¼�X6�Õ ³ Q#ÄPÛ Q#ôPÀ!¸ÅôPÀ68)Pæ�Ð|Z02<+�+ »*V�+.-0Z0V ² 68/(9�×�×hØ ¼�X6�Õ ³ Q�¿ F�24/�DMÁ4,

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

6þ#7Bÿ Cx¶ED5,�G�ò�2 '<] à�) ] /.68)Pæ�Ðb�|-02�ÕV�æ�2<+ ­ æ + ® )\Z ½ Ð|Ðb´MV ^#' -0V�) ]�ó � ] ÕVMæ�25+ ­ +32 ^<® [ )\Z�ë ó 2 ' /+.) ]H'<² ´M2<ì�¼�X6�Õ ³ ¼ ^ �|254!�|´M2#Z�+

Page 189: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5¿

ÐH2�Z3[ )\Z0æ ² 2<+.-Ô?V�-0� Ö,2�Z0Ñ�´�) ]|± ­ V;¸ 2,¸MO ^ 2 ] -0Z ' ´�VMá�2<4�+ ^ �b2<4!�|´�V ]|±r' -?-0�b2�4!V�+.¯ ® )PZ?Ö,2�Z�Ñ�+.�|)PZ�- ­ V(¸ö2,¸�O ^ 2 ] /-0Z ' ´�VMá�2<4�+ ^ �|2<4!�b´MV ]b±�' -�-��|2��|)w+3- ® æ 'TÎ VMæ"�|æË4!V�+.¯ ^ )\æ�æ 'T] 4�Ï,�|2��b2�´M2 ]|± -��H+l¸�ï��|2 ] -��|2�ë ² 2<+.-�ì^ 2 ] -0Z ' ´�VMá�2<4 'T] 4"4!VW+3-0Z�V ² �b-02<4"+ ^ �|2<4!�b´M2�ZL+ ' Z�2 ^ )\æ�Ð ' Z02<4pOw4!V�+.-0Z0V ² �|-�2<4�+ ^ �|2<4!�b´MV ]b± Ð|Z0)<Ö�V�4!25+�2<Ï,�|VMÖ ' /´M2 ] -B)PZ8+.�|ÐH2�Z0V�)PZRæ�2 'T] Z025+3ÐH) ] +.2?-0V�æ�2<+o[ )PZ�æ�),+.-�)<[p-��|22 Î ÐH2�Z�VMæ�2 ] -�+H�H+3V ]|± -��|2��uX 'T] 4�»uî6 4�V�+3¯Z025Ï}�|25+3-?-0Z 'P^ 25+l¸8Õ�|2u[ �|´�´�+3Ñb+3-�2�æ�-�Z 'P^ 2<+lO|�|)<Ô�2�Ö,2�Z�O ' Z02 ² 2�-0-�2�Z�+32�Z�Ö,2<4 ² Ñ ^ 2 ] -0Z ' ´�VMá�2<4"+ ^ �|2<4��|´M2�ZL+l¸Õ�|VW+�VW+u4!�|2�-�) -0�|2"´MV�æ�VM-�2<4 ^ )\æ�æ 'T] 4�Ï,�|2��|2�´�2 ]|± -���VMæ�ÐH)w+32<4�) ] 2 '\^ ��4�V�+3¯ ^ )Pæ�Ðo) ] 2 ] -*)<[?-��|24!VW+3-0Z�V ² �b-02<4 + ^ �|2<4��|´M2�Z�VMæ�Ðb´M2�æ"2 ] - ' -0V�) ] +Þ¸

8:9<; =?>A@CBED�F�GIHIJCK LMHON�@ PQJCRTSVU�W XYN�HZS[J \?U]S[W ^�_�`�SEa�BEb XcJ�D^AdeBEGZSYLfb

g���h��ji kl"$!#monqpsr��pQ! ø�ù �# ]��pQ!¼,2 ^ -�VM) ] ¹w¸MQP¸�Qu+.�|)<Ô�+�-0� ' --��|2 ½ ¼�X8Õ ³­ ¿ ®8'<] 4 ½ ¼�X6�Õ ³­ ¿ ®�' ´ ± )PZ�VM-0�bæ +�� ' Ö,2�æ�2 'T] Z�2<+3ÐH) ] +32

-0V�æ�2<+?2<Ï,�|VMÖ ' ´�2 ] - ­ Ô?V�-0�|V ]�' [ 2�ÔüÐo2#Z ^ 2 ] - ® -0) -0�|)w+32�)<[?-��|2�¼}X�Õ ³ 'T] 4Y¼�X6�Õ ³Ó' ´ ± )\Z0VM-��|æ +ÞOpZ02�/+3ÐH2 ^ -0VMÖ,2#´MÑ,¸ ³ V ± �|Z025+�¹,¸ÅÄP¿5äb¹,¸ÅÌ!Qm+3�b)TÔÝ-0� ' - -0�|2 'T± 2�/;+.2 ] +.VM-0V�Ö,2 ¼�X8Õ ³�' ´ ± )PZ0V�-0�|æ�+ ' ´W+3)mÐ|Z0)<Ö�V�4!22<Ï,�|VMÖ ' ´M2 ] -�)PZ�+3�|ÐH2�Z�VM)PZ"+.- ' Z0Ö ' -�VM) ] Z02<+.V�+.- 'T]e^ 2 ­;' +�æ�2 ' +.�|Z02<4 ² Ñm+0Ï,� ' Z�2<4 ^ ),2lå ^ VM2 ] -L+�)<[uÖ ' Z0V ' /-0V�) ]p® ¸ ½ 4|4�V ]|±"'<± 2�/(+32 ] +3VM-�VMÖ�VM-.Ñ�-�)�¼�X8Õ ³�' ´ ± )PZ�VM-0�bæ +V ] 4!VW+3-0Z�V ² �b-02<4 + ^ �|2<4��|´M2�Z?V�æ�Ð|´�2�æ�2 ] - ' -�VM) ] +V�+�-��|2�Z�2l[ )PZ�2 ± 2 ] 2�Z ' ´�´MÑ ' 4!Ö!VW+ '<² ´M2,¸ ³ �|Z�-0�|2#Z0æ�)\Z02,OR-��|2 'T± 2#/;+.2 ] +3V�-0V�Ö,2x¼}X�Õ ³ü' ´ ± )PZ�VM-��|æ +��e+3� ' ´M´MÑÐ|Z�)TÖ�V�4�2 ² 2�-�-02�Z�+3- ' Z�Ö ' -0V�) ] Z�2<+3VW+3- '<]H^ 2�-0� '<] -0�b2u9�1?à*/ ²H' +32<4 ' ´ ± )PZ0V�-0�|æ�+�[ )\Z ' ´M´HÔ�)PZ0¯�´M) ' 4|+82 Îb^ 2�Ð|-IJ�K�K:NP¸

çutH�m¢�þ|A<> èvt4wYé">yx<�{z�¤T�BC���µBÿ�>|wB@�þ3x�x<�BC?}CtoèOxÕ '<² ´M2�¹w¸Êº�+.�|)<Ô�+�-��|2�æ�2 'T] Z�2<+3ÐH) ] +32 -0V�æ�2<+�[ )\Z�ë0Z02 ' +3) ]H'T² ´M2<ì ^ 2 ] -0Z ' ´MV�á�2<4 'T] 4m4!VW+3-�Z0V ² �|-02<4

+ ^ �|2<4��|´M2�Z?V�æ�Ð|´�2�æ�2 ] - ' -�VM) ] +��H+.V ]|± -0�b2 ½ ¼�X6�Õ ³­ ¿ ®~' ´ ± )PZ�VM-��|æ�¸ ½ �b-0)Pæ ' -0V ^ Ð|Z�2l[ 2�- ^ �|V ]|± ) ] [ �|´M´Z02 ' 4��|V�-�+�Ô ' +R4!VW+ '<² ´M2<4�[ )\ZR-0�b2<+32�+.VMæ"�|´ ' -0VM) ] +lO ' +R-0�|VW+t-.Ñ�Ðo2?)<[EÐ|Z02l[ 2#- ^ �|V ]|± 4!2 ± Z ' 4!2<+�ÐH2�Z.[ )PZ0æ 'T]H^ 2Ô?�|2 ] + ^ �|2<4!�b´MV ]b± -��|2z»uî6Ù-�Z '\^ 2<+l¸�Õ�|2 ^ 2 ] -0Z ' ´MV�á�2<4 + ^ �|2<4��|´M2�Z�´MVW+3-0254�[ )PZ�2 '\^ ��-0Z '\^ 2 ^ ) ]!ßH± �|Z ' /-0V�) ] Z02#Ð|Z02<+.2 ] -�+�-��|2u�|)w+3-�/ ²H' +32<4 )PZ�4!VW+3¯�/ ²e' +3254�VMæ�Ð|´M2�æ"2 ] - ' -0V�) ] -�� ' -?Ð|Z�)�4!� ^ 25+�-��|2u´M)<Ô�2<+3-�æ�2 'T]Z025+3ÐH) ] +.2�-�VMæ�2w¸�¼,V�æ�VM´ ' Z0´�Ñ,O8-0�|2 ^ �|),+.2 ] 4!VW+3-0Z�V ² �b-02<4�+ ^ �|254!�|´M2#Z�+�Ð|Z0)<Ö�V�4!2�-0�|2�´�)TÔ�2<+3-�æ�2 'T] Z02�/+3ÐH) ] +32�-�VMæ�2<+ ' æ�) ]|± -0�|2r4!V�+.-0Z0V ² �|-�2<4�VMæ�Ð|´�2�æ"2 ] - ' -0VM) ] ++.-0�H4�VM2<4p¸ ³ )\Z ' ´M´B+.V Î -0Z 'P^ 2<+ÞO|-0�|2�ë ² 2<+.-�ì4!VW+3-0Z�V ² �b-02<4�+ ^ �|254!�|´M2#Z*Ð|Z�)<Ö!VW4!2<+ '<] 2<Ï,�|V�Ö ' ´M2 ] -�)PZz+3�|ÐH2�Z�VM)\Z�æ�2 'T] Z�2<+3ÐH) ] +32"-0VMæ�2�-0) -��|2�ë ² 2<+.-�ì^ 2 ] -0Z ' ´�VMá�2<4�+ ^ �|254!�|´M2#Z�¸ ³ )PZ�-0�|2uÂEÃbaTc,J�-�Z '\^ 2,O,4!VW+3-�Z0V ² �|-02<4z+ ^ �|2<4!�b´MV ]b± 4!Z0)\ÐH+Ræ�2 'T] Z�2<+3ÐH) ] +32�-0VMæ�2<+² Ñ ÌPÄ,Ò 'T] 4�Q�Ì,Ò [ )\Z�XRZ02<+.2�2�¯ '<] 4 ³ �|´�´ ^ )\æ�æ 'T] 4�Ï,�|2��|2#V ]|±"^ ) ]!ßH± �|Z ' -0VM) ] +lOHZ025+3ÐH2 ^ -�VMÖ,2�´�Ñ,¸

Õ '<² ´M2�¹w¸Ê¿�+.�|)<Ô�+�-��|2 +�Ï}� ' Z02<4 ^ ),2Þå ^ V�2 ] -�+u)T[hÖ ' Z0V ' -�VM) ] [ )\Z�-0�b2�+ ' æ�2 ^ 2 ] -0Z ' ´�VMá�2<4 'T] 4Y4�V�+3/-0Z�V ² �b-02<4m+ ^ �|2<4��|´M2�ZzVMæ�Ðb´M2�æ"2 ] - ' -0V�) ] +Þ¸xï�V�-0�m) ] 2�2 Î|^ 2#Ð|-0V�) ] O84!VW+3-�Z0V ² �|-02<4í+ ^ �|2<4!�|´�V ]|± ÐbZ0)<Ö!VW4!2<+2<Ï,�|VMÖ ' ´M2 ] -)\Z�+3�|ÐH2�Z�VM)\Zu+.- ' Z�Ö ' -0V�) ] Z�2<+3VW+3- '<]H^ 2z-0) ^ 2 ] -0Z ' ´MV�á�2<4�+ ^ �|254!�|´MV ]|± ¸�ï��|2 ] + ^ �b2<4!�|´�V ]|± -��|2IJ�K�K:N�-0Z 'P^ 2u[ )\Z�4!V�+.¯|+8Ô?VM-0��XRZ025+32�2�¯ ^ )\æ�æ 'T] 4�Ï,�|2��|2#V ]|± O ' �b),+3-�/ ²e' +3254 ½ ¼�X6�Õ ³­ ¿ ® VMæ�Ðb´M2�æ"2 ] /- ' -0V�) ] � ' + ' Q�Ì}Ò�´�)TÔ�2�Z?+�Ï}� ' Z0254 ^ ),2lå ^ V�2 ] -8)<[8Ö ' Z0V ' -�VM) ] ¸

g���h���h ÷ ���$�~�A��! ø p� ù �# ]��ps!Õ�|V�+z+32 ^ -0VM) ] 2 Îb' æ�V ] 2<+?-0�|2�Ðo2#Z3[ )PZ�æ 'T]e^ 2�)<[h4!V�+.-0Z�V ² �|-�2<4�+ ^ �|2<4!�|´�2�Z�VMæ�Ðb´M2�æ"2 ] - ' -0V�) ] +*�e+3V ]b±

Ä}° ' ´ ± )\Z0V�-0�|æ +Þ¸ ³ )PZ ^ ) ] Ö,2 ] VM2 ]e^ 2,Op-��|2��b),+3-�/ ²e' +3254 '<] 4 4!VW+3¯�/ ²e' +3254 ^ 2 ] -0Z ' ´MV�á�2<4�+ ^ �|254!�|´M2#Z�+*�H+.2

Page 190: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹\¹

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<C�¶pD�_bÁ�G�IJ�KMK{NPO�Q\¸y¹<º<S�UH»*VW+3-0Z�V ² �b-02<4�¼ ^ �|2<4!�b´MV ]b±�½ ´ ± )PZ�VM-��|æ¾X�2�Z.[ )PZ�æ 'T]H^ 2

Page 191: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5Û

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.CR (Host)« SSTF.CW.CR¬

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

1

2

3

4

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.CR (Host)« SSTF.CW.CR¬

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<Cx¶ED�_H¶pG?ÂEÃ|aTcwJ�ORQP¸ÅÄPº<S�UH»*V�+.-0Z�V ² �|-�2<4�¼ ^ �|2<4!�|´�V ]|±r½ ´ ± )PZ�VM-0�bæ�X�2#Z3[ )PZ�æ 'T]e^ 2

Page 192: Aggressive Centralized and Distributed Scheduling ofDisk Requests

QT¹5ô

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

2

4

6

8

10

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

2

4

6

8

10

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

=?>�@HµBA<Cx¶ED`_bÉ�G*fhg l�i�Æ�Ç#klOHÄ!¸ÅºTS�Ub»*V�+.-0Z0V ² �|-�2<4�¼ ^ �b2<4!�|´�V ]|±r½ ´ ± )PZ0V�-0�|æÈX�2�Z3[ )\Z0æ '<]H^ 2

Page 193: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û\À

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

25

30

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

5

10

15

20

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<C�¶pD�_*2�G*ÂEn�gMi ÈpÂeOpÄ�¸ÊºTSrUH»*V�+.-0Z0V ² �|-�2<4�¼ ^ �|2<4!�b´MV ]b±"½ ´ ± )PZ0V�-0�|æËX�2�Z.[ )PZ�æ 'T]H^ 2

Page 194: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û�Q

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

2

4

6

8

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

2

4

6

8

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

=?> @Hµ�A<C�¶pD0)4/�G�q2l0s!JtljOEQP¸ÊÀ<S�UH»*VW+3-0Z�V ² �b-02<4�¼ ^ �|2<4!�b´MV ]b±�½ ´ ± )PZ�VM-��|æ�XB2�Z3[ )\Z0æ '<]H^ 2

Page 195: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û\Ä

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

2

4

6

8

10

12

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨ C-LOOK¦ SSTF§ SPCTF¨ ASPCTF(6)¨Disk-Based Scheduling Algorithm©

0

1

2

3

4

5

6

Squ

ared

Coe

ffici

ent o

f Var

iatio

n

� CQ = 4CQ = 16CQ = 128

C-LOOK.CW.SSR (Host)« SSTF.CW.SSR¬

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

=?>�@HµBATC�¶ED5)�FHG*ÆuJ1k|NQl�v OpQP¸ÅÀTS�Ub»*V�+.-0Z�V ² �|-�2<4�¼ ^ �|2<4!�|´�V ]|±r½ ´ ± )PZ�VM-0�bæ¾X�2�Z.[ )PZ0æ 'T]H^ 2

Page 196: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û\Ì

Õ�Z '\^ 2 �*),+.-�¼ ^ �|254 »*V�+.¯�¼ ^ �|2<4 ò�2 'T]�ó 25+3м ^�' ´�2 ­;' ´M´8¸:68ï ® ­(' ´�´8¸y¼|¼ óu® 6?° ÕVMæ�2 ­ æ + ®682#´M´M) 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® ¸y6 ó Q QPQ�º�¸ÊÌ\ÛQP¸:¹<º »*V�+.-0Z0V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q#¿ FoF�)�D�É�)

¼ ]H' ¯,2 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® ¸y6 ó Q ÌPÌ�¸ÊôPÄQP¸ÅÄPº »*V�+.-0Z0V ² 68/(9�×�×uØ�¸:6 ó ¼�X6�Õ ³ ¸:¼|¼ ó Í _H_ED52p·

½ V�Z0/ ó +.Ö 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ ÄPÌ�¸ÊºPÀÄ�¸Êº »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q#¿ _H_EDMÉp·

¼ ^ V�/;Õ*¼ 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ QlÍb¸Ê¿TÍÄ�¸Êº »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q#¿ F�)�D52�F

×*ZL4!2�Z 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Q�Û�¸ÊÀPôQ\¸ÊÀ »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�ÄPÛ Q�Û�¸ÊÀPô

ó 2�ÐH)PZ�- 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ ÄPÌ�¸ÊôP¿Q\¸ÊÀ »*V�+.-0Z0V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�ÄPÛ ÄPÌ�¸ÊôP¿

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

Õ�Z '\^ 2 ��),+3-�¼ ^ �|2<4 »*VW+3¯�¼ ^ �|254 ò�2 'T]�ó 25+3м ^�' ´�2 ­;' ´�´8¸y68ï ® ­;' ´M´8¸:¼|¼ óu® 6?° ÕVMæ�2 ­ æ + ®682#´M´M) 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Q�ÀPÛ�¸Ê¿\¿QP¸:¹<º »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸:¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Í F3/p_ED�¶#)

¼ ]H' ¯,2 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ ÄPº�¸ÊÀTÍQP¸ÅÄPº »*V�+.-0Z0V ² ¼|¼�Õ ³ ¸:6 ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Í _EFHDMÉp¶

½ V�Z0/ ó +.Ö 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Ä!Q\¸MQ�ÌÄ�¸Êº »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ Ä!Q\¸MQPQ

¼ ^ V�/;Õ*¼ 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Q�Ä�¸y¹<ôÄ�¸Êº »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ Q�Ä�¸y¹P¹

×*ZL4!2�Z 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ QT¹w¸y¹<ºQ\¸ÊÀ »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:68ïõ¸y¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ QT¹w¸y¹<º

ó 2�ÐH)PZ�- 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ ÄPÌ�¸öÍ,ºQ\¸ÊÀ »*V�+.-0Z0V ² 68/(9�×�×hØ�¸:68ïõ¸y¼|¼ ó ¼�X6�Õ ³ ¸y¼b¼,ïõ¸y¼|¼ ó Q�ÄPÛ ÄPÌ�¸öÍ,º

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

6þ#7Bÿ Cx¶ED`·EG�ò�2 '<] ó 2<+3ÐH) ] +32�ÕV�æ�2<+�[ )PZ�ë ó 2 ' +3) ]H'T² ´M2<ì ½ ¼�X6�Õ ³­ ¿ ® ¼ ^ �b2<4!�|´�2�Z�+Þ¸������ ���<�j���T����T�u���0�$�v��� � � ���I����� ��� �$� ��� � � � �<�

Page 197: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û<Í

Õ�Z '\^ 2 �*),+.-u¼ ^ �|2<4 »*VW+3¯�¼ ^ �|2<4 ¼}Ï}Zu68),2 ܼ ^�' ´M2 ­;' ´M´�¸y68ï ® ­;' ´M´8¸y¼b¼ ó�® 6?° )T[�- ' Z682�´M´�) 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® ¸y6 ó Q F�/�D5)HÉQ\¸y¹5º »*VW+3-0Z�V ² 68/(9�×�×uØ�¸:¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�¿ QPQ\¸ÊôP¿

¼ ]H' ¯,2 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® ¸y6 ó Q QlÍb¸MQ�ÄQ\¸ÊÄ\º »*VW+3-0Z�V ² 68/(9�×�×uØ�¸:6 ó ¼�X6�Õ ³ ¸:¼|¼ ó Í FHD�¶*,

½ V�Z0/ ó +.Ö 682 ] -�Z ' ´ ½ ¼}X~6�Õ ³�­ ¿ ® Q�ÄPÛ Ì!¸Å¿PôÄ!¸Êº »*VW+3-0Z�V ² ¼b¼�Õ ³ ¸y¼b¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�¿ FHD�·*2

¼ ^ VM/(Õ*¼ 682 ] -�Z ' ´ ½ ¼}X~6�Õ ³�­ ¿ ® Q�ÄPÛ ¿!¸�QlÍÄ!¸Êº »*VW+3-0Z�V ² ¼b¼�Õ ³ ¸y¼b¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�¿ _ED�¶*2

×�Z�4!2#Z 682 ] -�Z ' ´ ½ ¼}X~6�Õ ³�­ ¿ ® Q�ÄPÛ QP¸�Q�ÄQP¸ÊÀ »*VW+3-0Z�V ² 68/(9�×�×uØ�¸:¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�ÄPÛ QP¸�Q�Ä

ó 2#Ðo)\Z0- 682 ] -�Z ' ´ ½ ¼}X~6�Õ ³�­ ¿ ® Q�ÄPÛ QP¸ÅÄPºQP¸ÊÀ »*VW+3-0Z�V ² 68/(9�×�×uØ�¸:¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼ ó Q�ÄPÛ QP¸ÅÄPº

­;',® XRZ025+32�2�¯ 68)Pæ�æ 'T] 4 °*�b2��|2�V ]|±

Õ�Z '\^ 2 ��),+3-u¼ ^ �|254 »*V�+.¯�¼ ^ �|2<4 ¼}Ï}Zu68),2 ܼ ^�' ´M2 ­;' ´�´R¸:68ï ® ­(' ´�´8¸y¼|¼ óu® 6?° )T[�- ' Z682�´M´�) 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Q�Ä�¸y¹,QQ\¸y¹5º »*VW+3-0Z�V ² ¼|¼�Õ ³ ¸:¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼,ïõ¸:¼|¼ ó Í FHFHDMÉ42

¼ ]H' ¯,2 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Ä!¸ÅÌPÀQ\¸ÊÄ\º »*VW+3-0Z�V ² ¼|¼�Õ ³ ¸y6 ó ¼�X6�Õ ³ ¸:¼|¼,ïõ¸:¼|¼ ó Í FHD�ÁHÉ

½ V�Z0/ ó +.Ö 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ QP¸ÅÄPÄÄ!¸Êº »*VW+3-0Z�V ² ¼|¼�Õ ³ ¸:¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼,ïõ¸:¼|¼ ó Q�¿ QP¸ÅÄPÌ

¼ ^ VM/(Õ*¼ 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ Ä!¸ÅÄPºÄ!¸Êº »*VW+3-0Z�V ² 68/;9�×�×hØ�¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼,ïõ¸:¼|¼ ó Q�ÄPÛ Ä!¸ÅÄTÍ

×�Z�4!2#Z 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ QP¸�Q�ÛQP¸ÊÀ »*VW+3-0Z�V ² 68/(9�×�×hØ�¸:68ïõ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼,ïõ¸:¼|¼ ó Q�ÄPÛ QP¸�Q�Û

ó 2#Ðo)\Z0- 682 ] -�Z ' ´ ½ ¼�X6�Õ ³­ ¿ ® Q�ÄPÛ QP¸ÅÄPÛQP¸ÊÀ »*VW+3-0Z�V ² 68/(9�×�×hØ�¸:68ïõ¸y¼|¼ ó ¼�X6�Õ ³ ¸:¼|¼,ïõ¸:¼|¼ ó Q�ÄPÛ QP¸ÅÄPÛ

­ ²p®�³ �|´M´R68)\æ�æ 'T] 4�°��|2��b2�V ]|±

6þ#7Bÿ Cx¶EDMÁ�G�¼�Ï,� ' Z02<4�68),2lå ^ V�2 ] -L+p)T[�- ' Z0V ' -0V�) ] [ )PZuë ó 2 ' +3) ]H'T² ´�2<ì ½ ¼�X6�Õ ³­ ¿ ® ¼ ^ �|2<4!�|´�2�Z�+Þ¸���$� �y�<�j��� ���T�u���0�$�v��� � � ���I����� ��� �$� ��� � � � �<�

Page 198: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û\º

-0�b2u+ ' æ�2�Ä,° ' ´ ± )PZ0V�-0�|æ7O ' ´�-0�|)\� ± ��-��|2h+32<Ï,�|2 ] -0V ' ´H+.-0Z02 ' æâ)PÐb-0VMæ�VMá ' -0VM) ] +R4!V Ü 2�Z�¸�Õ�|2u�|)w+3-0/ ²H' +32<4+ ^ �|2<4��|´M2�ZL+*�H+.2 ^ ) ]H^�' -02 ]H' -0V�) ] )<[�Ô?Z0VM-�2<+ '<] 4 +325Ï}�|2 ] -�V ' ´�+ ^ �|2<4!�|´�V ]|± )T[�Z02 ' 4|+Þ¸�Õ�|2 4�V�+3¯�/ ²H' +.2<4+ ^ �|2<4��|´M2�ZL+t�e+32�+325Ï}�|2 ] -�V ' ´�+ ^ �b2<4!�|´�V ]|± )T[�Z02 ' 4 'T] 4�Ô?Z�VM-02�Z02<Ï,�|2<+.-�+�Ô?�b2 ]"³ �|´M´ ^ )Pæ�æ 'T] 4�Ï,�|2��|2#V ]|±V�+2 ]H'T² ´�2<4p¸

�*),+.-0/ ²H' +.2<4�+ ^ �|254!�|´M2#Z�+ ' Z02 ' +0+.�|æ�2<4�-�)�� ' Ö,2?¯ ] )<Ô?´M2<4 ± 2�)T[�2 'P^ �"4!V�+.¯��Å+�æ 'TÎ VMæ��|æ ^ )Pæ�æ '<] 4Ï,�|2��|2�´M2 ]b± -0��¸]% ] )PZL4!2�Z�-0)�ÐbZ02�Ö,2 ] -8�|V ± ��Ð|Z�VM)PZ�VM-.Ñ�Z�2<Ï,�|2<+3-L+�[ Z�)Pæ ² 2�V ]b± 4!2�´ ' Ñ,2<4 ² Ñ�[ �|´�´o) ] / ² ) ' ZL4^ )\æ�æ 'T] 4�Ï,�|2��b2<+lO<�|),+.-0/ ²H' +.2<4"+ ^ �|2<4!�|´�2�Z�+�) ] ´MÑ�VW+0+.�|2´�)TÔmÐ|Z�VM)\Z0VM-.ÑuZ�2<Ï,�|2<+3-L+�-0)�4!V�+.¯|+�Ô?VM-�� ' -R´�2 ' +.-ÄPº,Ò�)T[�-0�|2�V�Z ^ )Pæ�æ 'T] 4"Ï,�|2��|2u2#æ�Ð|-.Ñ,¸BÕ� ' -�V�+ÞO|) ]H^ 2 ' 4�V�+3¯ �Ê+ ^ )Pæ�æ '<] 4"Ï}�|2#�|2�Z02 '\^ �|25+�¹<º,Ò�)T[æ '<Î V�æ��|æ O\) ] ´�Ñ��|V ± ��Ð|Z�VM)\Z0VM-.Ñ"Z02<Ï,�|2<+.-�+Ô?V�´M´ ² 2�Ð ' +0+3254�) ]�² Ñ�-0�|2��|)w+3-0/ ²H' +32<4�+ ^ �|2<4!�|´�2�Z�¸¢¡

³ )PZu´�V ± ��-�Ô)PZ�¯!´�) ' 4|+lO�4�V�+3-�Z0V ² �|-0254�+ ^ �|2<4��|´M2�ZL+Ð|Z0)<Ö�V�4!2z-0�|2r+ ' æ�2�ÐH2�Z.[ )PZ0æ 'T]H^ 2 ' +�4�V�+3¯�/ ²H' +.2<4^ 2 ] -0Z ' ´�VMá�2<4�+ ^ �|2<4!�b´M2�ZL+lOB+3V ]H^ 2 ' ´M´8ÐH2 ] 4�V ]|± Z02<Ï,�|2<+.-�+u-.Ñ!Ð|V ^�' ´�´MÑ ß -�Ô?VM-0�bV ] -0�|2") ] / ² ) ' Z�4dÏ,�|2��b2<+l¸³ V ± �|Z�2<+�¹,¸ÅÌPÄ 'T] 4ñ¹w¸ÊÌ\ÌxÐ|Z�2<+32 ] -zæ�2 'T] Z02<+.Ðo) ] +32 -�VMæ�2<+ '<] 4Yæ�2 'T]�] ) ] / ^ )\æ�Ð|�|-�2�-0V�æ�2<+*[ )PZ�-��|2ÛT/ �H+.2�Z�ÂoúPÃ}ÆzûuJÞÃ-0Z 'P^ 25+l¸ ³ )PZ ^ ) ]!ßH± �bZ ' -�VM) ] +�Ô?VM-��zX�Z�2<+32#2�¯ ^ )Pæ�æ '<] 4�Ï}�|2#�|2�V ]b± O ^ )\æ�æ 'T] 4*Ï,�|2��|2´M2 ]|± -��H+u)T[?Í )\Z�Q�¿ Ð|Z0)<Ö�V�4!2�-��|2�´M)<Ô25+3-uæ�2 'T]�] ) ] / ^ )Pæ�Ð|�|-02�-�VMæ�25+l¸�¼|¼�Õ ³ )P�|-�Ðo2#Z3[ )PZ�æ + ³ 6 ³ ¼HO68/(9�×�×hØ"O '<] 4Y-��|2�¼�X8Õ ³ / ²H' +32<4 ' ´ ± )PZ�VM-0�bæ + ² Ñ Ä}Ò�¸�Õ�|2 V ] [ 2#Z0VM)\Z�ÐH2�Z3[ )\Z0æ '<]H^ 2�)<[�¼�X8Õ ³ VW+4!�|2�-�) 'T] � ] [ )PZ�-0� ]H' -02") ] / ² ) ' Z�4 ^�'\^ �b2�4!2<+.V ±\]�^ �|)\V ^ 2 ­ +32�2"+.2 ^ -0V�) ] º!¸MQ\¸ÊÌ ® ¸ ³ )PZ ³ �|´�´ ^ )Pæ�æ '<] 4Ï,�|2��|2�V ]|±?^ ) ]!ßH± �|Z ' -0V�) ] +ÞO '?^ )Pæ�æ '<] 4�Ï}�|2#�|28´M2 ]|± -0��)T[bÍ�Ð|Z0)<Ö�V�4!2<+H-0�|28´�)TÔ�2<+3-�æ�2 'T]u] ) ] / ^ )Pæ�Ð|�|-02-0V�æ�2<+Þ¸�Õ�|2*¼}X�Õ ³ / ²H' +32<4 ' ´ ± )PZ0V�-0�|æ�+p-0Z ' VM´H¼|¼�Õ ³ ² Ñu´�2<+0+�-0� 'T] QTÒ Ô?�|2 ]�³ �|´M´ ^ )Pæ�æ '<] 4uÏ,�|2��|2#V ]|±V�+2 ]H'T² ´�2<4p¸

³ V ± �|Z025+�¹,¸ÅÌTÍ '<] 4�¹,¸ÅÌPº�+.�|)<ÔÙæ�2 'T] Z025+3ÐH) ] +.2�-0VMæ�2<+ 'T] 4 ' Ð|Ð|´�V ^�' -0VM) ] Z0� ] -0V�æ�2<+t[ )\Z-0�b2 I8NQj�ikmljJ�Ç�Ç8Ô)PZ�¯!´�) ' 4p¸Õ�b2�æ 'TÎ VMæ"�|æ ^ )\æ�æ '<] 4�Ï,�|2��b2u´M2 ]b± -0� '�Ü 2 ^ -�+ ' Ð|Ð|´MV ^�' -�VM) ] Z�� ] -�VMæ�25+ ² Ñ"´M2<+�+-0� 'T] Q<Ò�¸�Õ�|2�¼�X8Õ ³ / ²H' +.2<4 ' ´ ± )\Z0VM-��|æ +�)P�|-�Ðo2#Z3[ )PZ�æ ³ 6 ³ ¼ '<] 4Y-��|2�9�1?à*/ ²e' +3254 ' ´ ± )\Z0VM-��|æ +² Ñ Ä5ä}Ì}Ò�¸

çutH�m¢�þ|A<> èvt4wYé">yx<�ÙçzC�w�x<A<þ|ÿ >�ê,C��£z�¤<��C��Bµ�ÿ >¤wB@Õ '<² ´M25+x¹,¸:¹ 'T] 4�¹w¸ÊÛ ' ´M´�)<Ô ^ )\æ�Ð ' Z�V�+.) ] ² 2#-3Ô�2�2 ] -��|2Ùë ² 2<+3-Lì ^ 2 ] -0Z ' ´�VMá�2<4 '<] 4Ó4!VW+3-�Z0V ² �|-02<4

Ä}°ñ+ ^ �|2<4��|´M2�ZL+l¸ ³ )\Z ^ ) ]�ßH± �|Z ' -�VM) ] +�Ô?VM-���2�V�-0�|2�ZBXRZ�2<+32�2#¯�)\Z ³ �|´�´ ^ )Pæ�æ '<] 4uÏ,�|2��|2#V ]|± OP4!VW+3-�Z0V ² �|-02<4VMæ�Ð|´M2�æ"2 ] - ' -0V:) ] +�Ð|Z0)<Ö�V�4!27+3�|ÐH2�Z�VM)\Z�Ö ' ´��|2<+�[ )\Z�-��|2 ' Ð|Ð|´�V ^�' -0VM) ] /(+3ÐH2 ^ V ßE^ ÐH2�Z.[ )PZ0æ 'T]H^ 2 æ�2#-0Z0V ^ +l¸»*VW+3-0Z�V ² �b-02<4 + ^ �|2<4!�b´M2�ZL+��H+3V ]|± 9�1?à*/ ²H' +.2<4 ' ´ ± )PZ0V�-0�|æ�+�ÐbZ0)<Ö!VW4!2�Í!Ò '<] 4ÓÀ�¸Êº}Ò ² 2�-�-02�Z�Ðo2#Z3[ )PZ�/æ '<]H^ 2*[ )\Z�ÛT/ �H+32�Z�ÂEú\Ã}ÆzûuJÞà '<] 4dI8NQj�kml�J0Ç�ÇÞO!Z�2<+3ÐH2 ^ -�VMÖ,2�´�Ñ,¸ ³ )PZ�+ ^ �|2<4��|´M2�ZL+��H+.V ]|± [ �|´�´M/ ¯ ] )<Ô?´�2<4 ± 2' ´ ± )\Z0VM-��|æ +ÞOp4!VW+3-�Z0V ² �|-02<4�+ ^ �|2<4!�b´MV ]b± Ð|Z�)<Ö!VW4!2<+ ' À!¸ ÍTä�Ä�¸y¹\Ò¾Ðo2#Z3[ )PZ�æ 'T]e^ 2�VMæ�Ð|Z�)<Ö,2�æ�2 ] -R[ )PZh-0�|2<+.2Ô)\Z0¯�´M) ' 4|+Þ¸

g���h���� ����� ������������������ ��!#"$����!½*± 2#/;+.2 ] +3V�-0V�Ö,2�Ö,2#Z�+3V�) ] +�)T[E-��|2�[ �|´�´M/ ¯ ] )TÔ?´�2<4 ± 2 ' ´ ± )PZ0V�-0�|æ�+tÐ|Z�)<Ö!VW4!2 ± ),)�4�æ�2 'T] Z02<+.ÐH) ] +.2?-0VMæ�2<+

'T] 4�+.�|ÐH2�Z0V�)PZ�+.- ' Z�Ö ' -0V�) ] Z02<+.V�+3- 'T]H^ 2�[ )PZ�4!VW+3-�Z0V ² �|-02<4 + ^ �|2<4!�|´�V ]|± )T[�-0�|2 4!V�+.¯ÙZ�2<Ï}�b2<+3-�-�Z 'P^ 2<+l¸ï��|2 ] -0�|2 ë ² 2<+3-Lì ^ 2 ] -0Z ' ´MV�á�2<4 'T] 4Y4�V�+3-�Z0V ² �|-0254 ½ ¼}X~6�Õ ³�­ ¿ ® V�æ�Ð|´�2�æ�2 ] - ' -0V�) ] + ' Z�2 ^ )Pæ�Ð ' Z0254pO4!VW+3-0Z�V ² �b-02<4�+ ^ �b2<4!�|´�V ]|± Ð|Z0)<Ö�V�4!2<+´�)<Ô2�Z�æ�2 'T] Z025+3ÐH) ] +.2�-�VMæ�2<+ '<] 4 ² 2#-0-02#Z�+3- ' Z0Ö ' -�VM) ] Z025+3V�+.- '<]H^ 2,¸

³ )PZu´�V ± ��-�Ô)PZ�¯!´�) ' 4|+lO�4�V�+3-�Z0V ² �|-0254�+ ^ �|2<4��|´M2�ZL+Ð|Z0)<Ö�V�4!2z-0�|2r+ ' æ�2�ÐH2�Z.[ )PZ0æ 'T]H^ 2 ' +�4�V�+3¯�/ ²H' +.2<4^ 2 ] -0Z ' ´�VMá�2<4 + ^ �|2<4��|´M2�ZL+lO�+.V ]H^ 2 ' ´M´�ÐH2 ] 4!V ]|± Z�2<Ï,�|2<+3-L+�-.Ñ�Ð|V ^�' ´M´�Ñ ß -�Ô?VM-��|V ] -��|2m) ] / ² ) ' Z�4Ú4�V�+3¯Ï,�|2��|2<+Þ¸ ³ )\Z*-��|2�Û</��H+.2�Z�ÂEúPÃ}ÆzûuJÞà 'T] 4�I8NQj�kmljJ0Ç�Ç�-0Z 'P^ 25+lOH4!VW+3-0Z�V ² �b-02<4 Ä}°ü+ ^ �b2<4!�|´�2�Z?VMæ�Ðb´M2�æ"2 ] /

¥$¦v§�¨ª©�«�¬¤­I§�® ¯±°I¬|§�²�§�³j´µ¬|§�¯O¨�¶|« ·O¸�§¢¶¤«$®�¬|­�´<¬�¬|­�«�­�¯O®|¬�¬�´<¹±«�´<¨�´O©�¬¤§�ºO«�¶|¯±»¢«Q§�¨�®|«�»¢« ©�¬|§�¨I¼�¶¤«j·±¸I«$®|¬¤®Q½0¯O¶�®|«$¶¤ºv§¾©¿«OÀI§�¬�Á�´µ®¨I¯±¬s©�¯O¨I®¤§�Âv«$¶|« ½0¯O¶sÂ碮¤¹±Ä�Ū´µ®|«jÂ�©�«�¨Z¬¤¶.´µ»¢§�³$« Â�®.©¤­I«jÂøI»�§¢¨�¼ªÆ

Page 199: Aggressive Centralized and Distributed Scheduling ofDisk Requests

Q�Û\¿

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

Ë CQ = 4CQ = 16CQ = 128

­�Ì}® ò?Í ÌIÎ�ó ÍIÏ.Ð�Ð Î Ï�ÍrÕ�ÑMæ:Í

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

Ò CQ = 4CQ = 16CQ = 128

­ ²p® ò?Í ÌIÎ à�Ð Î#Ó$Ô ÐPæ�Ð*Õ#Ö ÍzÕ�ÑMæ×Í

Ø�Ù¤ÚHµsÛIÜx¶ Ý5)�Þ ß�ÂoúPÃ}Æzû�àÞÃ3á8ÛC(�Ï�ÍZâ<ϱãr»ÑyÏ$Ö â Ñ ² Õ#ÖjÍIä Ä}°¾¼�å<æ#ÍIä�Õ|´5Ñ Î|±�½ ´ ± Ð�â Ñ0Ö æ|æèçsÍvâ�é|Ъâ0æ ÌIÎ å±Íé|Ъâu»�ÑyÏ3¯*ÏÔ�Ñ5ÖjæCç�âjÍIÏ�ÍZÍ�¯ Ô ÐPæ�æ Ì�Î ä�°�Õ#ÍvÕ#ÍZÑ Î|±

Page 200: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê Û,¹

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

100

200

300

400

500

Mea

n R

espo

nse

Tim

e (m

s)

Ë CQ = 4CQ = 16CQ = 128

­�Ì}® ò?Í ÌIÎ�ó ÍIÏ.Ð�Ð Î Ï�ÍrÕ�ÑMæ:Í

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

100

200

300

400

Mea

n N

on-C

ompu

te T

ime

(ms)

Ò CQ = 4CQ = 16CQ = 128

­ ²p® ò?Í ÌIÎ à�Ð Î#Ó$Ô ÐPæ�Ð*Õ#Ö ÍzÕ�ÑMæ×Í

Ø�Ù¤ÚHµsÛIÜx¶ Ý5)4)�ß�ÂoúPÃ}Æzû�àÞÃ3á8ÛC(�Ï�ÍZâ<ϱãr»ÑyÏ$Ö â Ñ ² Õ#ÖjÍIä Ä}°¾¼�å<æ#ÍIä�Õ|´5Ñ Î|±�½ ´ ± Ð�â Ñ0Ö æ|æèçsÍvâ�é|Ъâ0æ ÌIÎ å±Íé|Ъâu»�ÑyÏ3¯*ÏÔ�Ñ5Öjæ ³ Õb´M´ Ô Ð\æ�æ ÌIÎ ä�°�Õ#ÍvÕ#ÍZÑ Î|±

Page 201: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê Û\Û

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

100

200

300

400

500

600

700

Mea

n R

espo

nse

Tim

e (m

s)

Ë CQ = 4CQ = 16CQ = 128

­�Ì}® ò?Í ÌIÎ�ó ÍIÏ.Ð�Ð Î Ï�ÍrÕ�ÑMæ:Í

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

ë CQ = 4CQ = 16CQ = 128

­ ²p®�½ Ð|Ðb´5Ñyå Ì Ö Ñ0Ð Î ó Õ Î Õ�ÑMæ×Í

Ø�Ù¤ÚHµsÛIÜx¶ Ý5)4,�ß:ì]íQj�kml<à0Ç�ÇOã�»ÑyÏ$Ö â Ñ ² Õ#ÖjÍIä Ä}°â¼�å<æ#ÍIä3Õb´5Ñ Îb±"½ ´ ± Ð�â Ñ0Ö æ|æîçQÍZâ�é|Ð�â�æ Ì�Î å±Íé|Ð�âh»Ñ�Ï3¯*ÏÔ�Ñ0Ö æCç�â ÍIÏ$ÍvÍ�¯ Ô Ð\æ�æ ÌIÎ ä�°�Õ#ÍZÕ#ÍvÑ Îb±

Page 202: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê Û\ô

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

100

200

300

400

500

600

700

Mea

n R

espo

nse

Tim

e (m

s)

Ë CQ = 4CQ = 16CQ = 128

­�Ì}® ò?Í ÌIÎ�ó ÍIÏ.Ð�Ð Î Ï�ÍrÕ�ÑMæ:Í

FCFS C-LOOKÇ SSTFÈ SPTF SPCTFÉDisk-Based Scheduling AlgorithmÊ

0

50

100

150

200

App

licat

ion

Run

Tim

e (s

ec)

ë CQ = 4CQ = 16CQ = 128

­ ²p®�½ Ð|Ðb´5Ñyå Ì Ö Ñ0Ð Î ó Õ Î Õ�ÑMæ×Í

Ø�Ù¤ÚHµsÛIÜx¶ Ý5)p· ß:ì]íQj�kml<à0Ç�ÇOã�»ÑyÏ$Ö â Ñ ² Õ#ÖjÍIä Ä}°â¼�å<æ#ÍIä3Õb´5Ñ Îb±"½ ´ ± Ð�â Ñ0Ö æ|æîçQÍZâ�é|Ð�â�æ Ì�Î å±Íé|Ð�âh»Ñ�Ï3¯*ÏÔ�Ñ0Ö æ ³ Õ|´M´ Ô Ð\æ�æ ÌIÎ ä�°�Õ#ÍZÕ#ÍvÑ Îb±

Page 203: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô\À

�ÐïÏ�Öu¼�å<æ#ÍIä »ÑyÏ.¯�¼�å<æ#ÍIä ò?ÍZÖ â Ñ�åÕ�â Ì åOÍ ­�Ì ´M´8¸ Ô ïõ¸y¼|¼ óu® Ô ° - Ì ´0Õ#ÍÛ Ó (�Ï$Ívâ Ô Í Î Ö â Ì ´ ¼b¼�Õ ³ ê ÌPÌPÌ�¸Êº\¿

¼,Ñ ÎHó1 Í Î »Ñ�Ï�Öjâ Ñ ² ¼b¼�Õ ³ ¼|¼�Õ ³ ê ¿ )�Þ*/�Ý�É�/Ô Í Î Ö â Ì ´ Ô]Ó�ð ×�×hØ ê Ä\Û ê ôPÀ�¸ÊÌ\ÛÔ ÐPæ�Ð#âjÍIÏ Ï »Ñ�Ï�Öjâ Ñ ² Ô]Ó�ð ×�×hØ Ô]Ó�ð ×�×hØ ê ¿ ñ!É42�Ý0)oÉ

­�Ì,® ç�â ÍÃÏ�ÍvÍ�¯ Ô ÐPæ�æ Ì�Î ä °Õ*ÍvÕ#ÍvÑ Î|±

��ÐTÏ�Öu¼òåµæ#ÍÃä »ÑyÏ.¯�¼�å<æ#ÍIä ò?ÍvÖjâ ÑyåÕ�â Ì å±Í ­.Ì ´�´8¸ Ô ïõ¸y¼b¼ ó�® ­.Ì ´M´8¸:¼|¼,ïõ¸:¼|¼ óu® Ô ° - Ì ´0Õ#ÍÛ Ó (óÏ�Ívâ Ô Í Î Öjâ Ì ´ ¼|¼�Õ ³ ê Ì\ÌPÌ!¸ÅºP¿

¼,Ñ ÎHó1 Í Î »ÑyÏ$Ö â Ñ ² ¼|¼�Õ ³ ¼|¼�Õ ³ Í )�Þ*/�ÝôÞH·Ô Í Î Öjâ Ì ´ Ô]Ó�ð ×�×hØ ê ÄPÛ ê ÛPÛ!¸:¹<ÀÔ ÐPæ�Ð#â ÍIÏjÏ »ÑyÏ$Ö â Ñ ² Ô]Ó.ð ×�×hØ Ô]Ó�ð ×�×hØ Í ñ�Ép¶ Ý`¶H·

­ ²p®�³ Õ|´M´ Ô Ð\æ�æ Ì�Î ä�°�Õ#ÍvÕ*ÍvÑ Î|±

6þ#7Bÿ|Üx¶ Ý`¶ ß�ò?Í ÌIÎ à�Ð Î#Ó$Ô ÐPæ�Ð*Õ#Ö Í�Õ�Ñ�æ:ÍIÏ ­ æ&Ï ® Ъ⠽ Ð|Ðb´5Ñyå Ì Ö Ñ0Ð Î�ó Õ Î Õ�ÑMæ:ÍÃÏ ­ Ï�ÍIå ® é|Ъâ�ë ó Í ÌIÓÏ$Ð Î4Ì<² ´5Í<ì ð�õ à Ó.õ�Ì Ï$ÍIä Ä}°Ú¼òåµæ#ÍÃä3Õ|´5ÍZâ<Ï

Page 204: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô ê

�ÐïÏ�Öu¼�å<æ#ÍIä »ÑyÏ.¯�¼�å<æ#ÍIä ò?ÍZÖ â Ñ�åÕ�â Ì åOÍ ­�Ì ´M´8¸ Ô ïõ¸y¼|¼ óu® Ô ° - Ì ´0Õ#ÍÛ Ó (�Ï$Ívâ Ô Í Î Ö â Ì ´ ¼�ç Ô Õ ³ ê ÌPÌPÄ�¸ÊÀ\º

¼,Ñ ÎHó1 Í Î »Ñ�Ï�Öjâ Ñ ² ¼�ç Ô Õ ³ ¼�ç Ô Õ ³ ê ¿ )�ÞbÁ�Ý|ñ�ñÔ Í Î Ö â Ì ´ ¼�ç Ô Õ ³ ê Ä\Û ê ÛPº�¸ÊÌ êÔ ÐPæ�Ð#âjÍIÏ Ï »Ñ�Ï�Öjâ Ñ ² ¼�ç Ô Õ ³ ¼�ç Ô Õ ³ ê ¿ ñ!É4,�Ý�·�Þ

­�Ì,® ç�â ÍÃÏ�ÍvÍ�¯ Ô ÐPæ�æ Ì�Î ä °Õ*ÍvÕ#ÍvÑ Î|±

��ÐTÏ�Öu¼òåµæ#ÍÃä »ÑyÏ.¯�¼�å<æ#ÍIä ò?ÍvÖjâ ÑyåÕ�â Ì å±Í ­.Ì ´�´8¸ Ô ïõ¸y¼b¼ ó�® ­.Ì ´M´8¸:¼|¼,ïõ¸:¼|¼ óu® Ô ° - Ì ´0Õ#ÍÛ Ó (óÏ�Ívâ Ô Í Î Öjâ Ì ´ ¼�ç Ô Õ ³ ê Ì\ÌPÄ!¸ÅÀPº

¼,Ñ ÎHó1 Í Î »ÑyÏ$Ö â Ñ ² ¼�ç Ô Õ ³ ¼�ç Ô Õ ³ Í )�Þ4Þ Ý524)Ô Í Î Öjâ Ì ´ ¼�ç Ô Õ ³ ê ÄPÛ ê ÛP¿!¸ÅÛPÄÔ ÐPæ�Ð#â ÍIÏjÏ »ÑyÏ$Ö â Ñ ² ¼�ç Ô Õ ³ ¼�ç Ô Õ ³ Í ñ�É4,�ÝMÉ4,

­ ²p®�³ Õ|´M´ Ô Ð\æ�æ Ì�Î ä�°�Õ#ÍvÕ*ÍvÑ Î|±

6þ#7Bÿ|Üx¶ ÝMÉ�ß�ò?Í ÌIÎ à�Ð Î#Ó$Ô ÐPæ�Ð*Õ#Ö Í�Õ�Ñ�æ:ÍIÏ ­ æ&Ï ® Ъ⠽ Ð|Ðb´5Ñyå Ì Ö Ñ0Ð Î�ó Õ Î Õ�ÑMæ:ÍÃÏ ­ Ï�ÍIå ® é|Ъâ�ë ó Í ÌIÓÏ$Ð Î4Ì<² ´5Í<ì"Ä}°ü¼�ç Ô Õ ³ ¼�å<æ#ÍIä�Õ|´5ÍvâöÏ

Page 205: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô\Ä

Ö Ì Ö Ñ0Ð Î Ï?Ð#â Ð<Ö�Ñyä3Í÷Ï�Õ|Ð4ÍvâjÑ5Ð�â�Ð4Ívâ�é|Ъâ0æ ÌIÎ å±Í�Ð<ÖTÍvâ�Í5ÏòÕ#Ñ�Ö Ì ´5Í Î ÖAå±Í Î Ö â Ì ´0ÑMávÍIä×Ï å<æ#ÍIä3Õ|´0Ívâ�Ñ�æ�Ð|´0Í�æ[Í Î Ö Ì ÖjÑ5Ð Î Ï­�Ì Ï�æ×Í Ì Ï$Õ#â ÍIä ² Ñ Ì Ð|Ð|´0Ñyå Ì Ö Ñ5Ð Î#Ó Ï3Ð4ÍIå±Ñ ß å*æ:ÍvÖjâ Ñ�åvÏ ® ¸

Õ�æ#Í:Í Î Ð4Ívâ Ñ�æ:Í Î Ö<ÏÑ Î Ö æ*ÑyÏøä�ÑyÏ Ï$Ívâ Ö Ì ÖjÑ5Ð Î Ï�æ#Ð<Ô�Ö æ Ì ÖVä3Ñ�Ï�Ö âjÑ ² Õ*Ö ÍIäùÏjåµæ*ÍIä3Õ|´0Ñ Î|± Ð#âjÐTÖ�Ñyä�ÍIÏuÐ�ÍZâ�é|Ð�â Óæ ÌIÎ å±Í�Í<ÏòÕ Ì ´]Ö Ð�Ъâ�Ï3´5Ñ ± æ�Ö0´�ÑúÏ�Õ|Ð4ÍvâjÑ5Ð�âuÖ Ð�Öjæ Ì ÖuÐ�é ² ÐªÖ æûæ#ÐïÏ�Ö Ó ²4Ì Ï�ÍIä Ì�Î äùä�ÑyÏ3¯ Ó ²4Ì Ï$ÍIäûå±Í Î Ö â Ì ´5Ñ�ávÍIäÏ å<æ#ÍIä�Õ|´5Ñ Î|± ¸"ïqÑ5Ö æúÖ æ*Í Ì ä#ä3Ñ5ÖjÑ5Ð Î4Ì ´üå±ÐTÏ$Ö ÌIÎ äùå±Ð\æ�Ð|´0Í Î Ñ0Ö.Ñ ² Í Î Í ß ÖöÏEÐIéóä3ÑyÏ$Ö â Ñ ² Õ#ÖjÍIä�Ï å<æ#ÍIä3Õb´5ÍvâYÑMæ ÓÐ|´0Í�æ:Í Î Ö Ì Ö Ñ5РΠϱá4Ö æ*ÑyÏ Î Í�Ô�Ï å<æ#ÍIä3Õ|´0Ñ Î|± Ð Ì â Ì ä3Ñ ± æèÑyÏâjÍIå±ÐPæ�æ:Í Î ä3ÍÃä×é|Ъâ�é|Õ#Ö Õ#âjÍ[æ*Ñ ± æ Ó Ð4Ívâ$é|Ð�â0æ Ì�Î å±Íå±Ð\æ�Ð#Õ#ÖjÍvâ�Ï.Ñ#Ï$Ö Í�æ&ÏÞ¸

Page 206: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ý�þ _fÿ������ �

ý S[J�>�GIF�D�H�JCK ��BEW XuU�� XcJ�D \�F&N�FCU]B � HZU]BE>AN�HZS[J�

Õ�æ#ÑyÏ�ä3Ñ�Ï Ï�ÍZâ Ö Ì Ö Ñ0Ð Î ä�Í�æ:Ð Î Ï�Ö â Ì ÖjÍIÏøÖ æ#Í�æ Ì� ЪâVÑMæ�Ð Ì å±ÖøÖjæ Ì Ö×ä3Ñ�Ï3¯ûâ Í<ÏTÕ#ÍIÏ$Ö�Ï å<æ#ÍIä3Õb´5Ñ Îb± æ Ì Ï[Ð ÎÏ�ÖjÐ�â ÌT± ÍúÏ$Õ ² Ï.Ñ#Ï$Ö Í�æ Ð4Ívâ�é|Ъâ0æ ÌIÎ å±Í ÌIÎ ä Ð<ÖTÍvâ Ì ´M´üÏ3Ñ*Ï�Ö Í#æýÐ4Ívâ�é|Ъâ0æ ÌIÎ å±Í,¸�»ÑyÏ.¯mÔ�Ð�â�¯!´0Ð Ì ä#Ï[åOÐ Î Ö Ì Ñ ÎÑ Î Ö Í Î Ï�Í ² Õ#â<Ï$Ö<Ï:Ð�é Ì å±Ö Ñ�Ö3Ñ0Ö3Ñïá�Ô�æ#Ñ�åµæqâjÍIÏ�Õb´5Ö�Ñ Î ´5Ð Î|± ÏòÕ*ÍvÕ#ÍIÏVÐ�ézÐ4Í Î ä3Ñ Î|± ä3ÑyÏ.¯ âjÍ<ÏòÕ*ÍIÏ�ÖöÏl¸ ½ ä�ÑyÏ3¯â Í5ÏòÕ#ÍÃÏ�Ö�Ï å<æ#ÍIä�Õ|´5Ívâ�Õ Ï�ÍIÏ?¯ Î ÐTÔ?´0ÍIä ± ÍEÐIé]Ö æ*ÍVÏ3Ñ*Ï�ÖjÍ�æ ÌIÎ ä ÐIé]Ö æ#Íuâ Í�´ Ì ÖjÑ5Ð Î Ï�æ#Ñ�Ð4Ï ² ÍvÖ.Ô�ÍvÍ Î Ñ Î ä3ÑMÖ�Ñyä�Õ Ì ´â Í5ÏòÕ#ÍÃÏ�Ö<ÏYÖ Ð�Ð#âjÐ�ä3Õ4å±Í Ì â Í<ÏTÕ#ÍIÏ$ÖøÐ�âöä3ÍvâjÑ Î|± Ö æ Ì ÖVÐPÐ#ÖjÑMæ:Ñ�ávÍIÏ�Ï.Ð�ÍÃå±Ñ ß å×å±â Ñ0Ö ÍvâjÑ Ì ¸ ½ ÏYÖ æ#Í Ì æ:Ð�Õ Î ÖuÐ�éÕ4Ï$ͱé|Õ|´�Ñ Î é|Ð�â�æ Ì ÖjÑ5Ð Î Ñ Î å±âjÍ Ì Ï$ÍIϱá Ì Ïjåµæ#ÍÃä3Õ|´5ÍZâ Ì åµæ#Ñ0Í�ÖTÍIÏ ² ÍvÖ ÖjÍvâuÐ4Ívâ�é|Ъâ0æ ÌIÎ å±ÍTá Ì ´ ² ÍvÑ0Ö Ì ÖYÖjæ#Í�å±ÐTÏ$ÖYÐ�éÑ Î å±â Í Ì Ï�ÍIäVÏjåµæ*ÍIä3Õ|´0Ñ Î|±óÌ ´ ± Ð�âjÑ5Öjæ|æ å±Ð\æ�Ð|´0Í Î Ñ0Ö.Ñ ÌIÎ äcâjÍIÏ�ЪÕ#â<åOÍ�â Í<ÏTÕ#Ñ5âjÍ�æ:Í Î ÖöÏ ­ Í,¸ ± ¸0áTÐ#âjÐ�å±ÍIÏjÏ�Ñ Îb± Ð4Ð<Ô�ÍZâÌ�Î ä�æ:Í�æ×Ð�â0Ñ ® ¸

(�Ï�ÍOé|Õ|´�Ï å<æ#ÍIä3Õb´5Ñ Îb± Ñ Î é|Ð�â0æ Ì Ö Ñ0Ð Î Ñ�Ï�Ð Ì âjÖ Ñ0Ö Ñ5Ð Î ÍIä ²4Ì Ï�ÍIäûÐ Î Ô�æ*ÍvÖ æ#ÍZâVÑ5Ö�å±Ð\æ:ÍIÏ÷é|âjÐPæ ë ÌT² Ð<ÖTÍ<ìÐ�âíë ² Í�´5Ð<Ô�ì Öjæ#ÍúÏ å<æ#ÍIä�Õ|´5Ívâ#¸ % Î é|Ð�â0æ Ì Ö Ñ0Ð Î é|â ÐPæ ë Ì<² Ð<ÖTÍ<ìúæ#Í�´MÐ ÏcÖjæ#ÍúÏ å<æ#ÍIä3Õb´5ÍvâVÖjÐùÑyä3Í Î ÖjÑ é ÑùÖjæ#ÍÑMæ�Ð�Ъâ Ö Ì�Î å±ÍYÐIé]Ñ Î ä�ÑMÖ�Ñyä3Õ Ì ´�â Í<ÏTÕ#ÍIÏ$Ö<Ï�ÖjÐ[Öjæ#Í Ì Ð|Ð|´5Ñ�å Ì ÖjÑ5Ð Î Ð#âjÐ�å±ÍIÏ Ï$ÍIÏ Ì�Î ä ÌIÎ Ñ&â Í5ÏòÕ#ÍÃÏ�Ö�Ð�âöä3ÍvâjÑ Î|± â Í ÓÏ�Öjâ Ñ�å±Ö Ñ0Ð Î ÏÞ¸8î Î Ð4Ívâ Ñ�æ:Í Î Ö<ÏQÑ Î Ö æ*ÑyÏ�ÔAÐ�â�¯[Õ4Ï$Í Ì Ï�ÑMæ�Ð|´5Í?Ð#âjÑ5Ъâ Ñ5Ö.Ñ�Ïjåµæ#Í#æ:Í�Ö æ Ì Ö�ål´ Ì Ï Ï$Ñ ß ÍIÏ Ì â Í<ÏTÕ#ÍIÏ$Ö Ì Ïæ#Ñ ± æ"Ð#â Ñ0Ð�â Ñ0Ö.ÑøÑ é Ì æ#ÐTÏ$Ö�Ð*â Ð�å±ÍIÏjÏ�Ñ�Ï ­ Ð�â8Ô�ÑM´�´ ² Í ® Ô Ì Ñ5Ö Ñ Î|± é|Ð�â]Ñ5Ö]ÖjÐøåOÐPæ�Ð|´0ÍvÖ Íw¸�îRÖTÍ Î Ö æ#Ñ�Ï]Ï�Ö â Ì Ñ ± æ�Ö�é|Ð�â ÓÔ Ì â<ä Ì Ð|Ð#â Ð Ì å<æ Ì ´�´5Ð<Ô�Ï Ì Ïjåµæ#ÍÃä3Õ|´5ÍZâ�Ö Ð&Ï$Ñ ±�Î Ñ ß å ÌIÎ Ö�´MÑ&ÑMæ�Ð#â Ð<ÖTÍ�Ð<ÖTÍvâ Ì ´M´sÏ.Ñ#Ï$Ö Í�æ¾Ð4Ívâ$é|Ð�â0æ Ì�Î å±Íw¸ ³ ЪâÍ Î*Ì æ�Ðb´5ÍTávÕ4Ï$Ívâ�ë Ö Ì Ï3¯*Ï0ìYÏ3Ð4Í Î ä Ì ÖR´0Í Ì Ï$Ö ê ¿,ÒÓ´5ÍÃÏ Ï�Ö ÑMæ×Í�Ô Ì Ñ0Ö Ñ Îb± Ð Î ä3ÑyÏ.¯V%��P×ûÑ ÎVÌ�Î Û Ó Õ Ï�Ívâ?ÂEú\Ã}Æzû�àÞÃÍIä3Ñ0Ö��#æ Ì ¯TÍ��Ãä3Í ² Õ ± Í Î Ö�Ñ5âjÐ Î æ:Í Î Ö ­.Ì Ï�Ñ Î ä�Ñyå Ì Ö ÍIä ² Ñ�Ö æ#Í�æ:Í ÌIÎ[Î Ð Î#Ó å±ÐPæ�Ð#Õ#Ö ÍóÖ ÑMæ×ÍTá Ì å±Ð Î Ï$Ívâ0Ö Ì Ö ÑMÖTÍÏ3Ñ*Ï�ÖjÍ�æ�Ð4Ívâ$é|Ð�â0æ Ì�Î å±Íhæ:ÍvÖ âjÑyå ® ¸

ïqÑ5Öjæ#Ð�Õ#Ö�Í Î Ð|´5Ñ�å±Ñ5Ö�¯ Î ÐTÔ?´0ÍIä ± ÍøÐ�é�â Í<ÏTÕ#ÍIÏ$Ö*Ð#âjÑ5Ъâ Ñ5ÖjÑ5ÍIÏ�ЪâÖjæ#ÍøÑ�æ�Ð Ì å±Ö�Ð�é]Ñ Î ä3Ñ�Ö3Ñ�ä3Õ Ì ´�âjÍ<ÏTÕ#ÍIÏ�ÖöÏ�Ð ÎÐ4Ívâ�é|Ъâ0æ ÌIÎ å±Í Ì�Î ä��vÐ�â�âjÍ�´5Ñ ÌT² Ñ�´5Ñ0Ö3Ñ ± Ð Ì ´�ϱá Ì Ï å<æ#ÍIä3Õ|´0ÍvâAå Ì�Î Ð Î ´�Ñ Ì Ö Ö Í#æ�Ð#Ö]Ö ÐzÐ#â Í�ÖTÍ Î Ö�Öjæ#ÍYÏ$Ö Ì â�Ö Ì Ö Ñ0Ð ÎÐ�é�å±â Ñ0Ö Ñyå Ì ´�âjÍ<ÏTÕ#ÍIÏ�ÖöÏ ² Ñhæ:Ñ Î Ñ�æ:Ñ:ávÑ Îb± âjÍIÏ3Ð4Ð Î Ï�ÍAÖ ÑMæ×ÍRÖ Ì â Ñ Ì�Î åOÍ ­ Ñ;¸ Í,¸5áOâ ÍIä3Õ å±Ñ Î|± Ï$Ö Ì â0Ö Ì ÖjÑ5Ð Î Ñ Îz± Í Î ÍZâ Ì ´ ® ¸½*± Í Ó Ï$Í Î Ï$Ñ5Ö Ñ�ÖTÍYÏ å<æ#ÍIä�Õ|´5Ñ Î|±�Ì ´ ± Ð�âjÑ5Öjæ|æ&Ï�Í Ü ÍIå±ÖjÑMÖTÍ�´�Ñ[âjÍIä3Õ4åOÍEâjÍIÏ3Ð4Ð Î Ï�ÍVÖjÑMæ:Í�Ö Ì â Ñ Ì�Î åOÍ ² Ñ ± Ñ�Ö3Ñ Î|± Ð*â Ñ ÓÐ�âjÑ5Ö.ÑøÖjÐøâjÍ<ÏòÕ*ÍIÏ�ÖöÏ�Öjæ Ì Ö]æ Ì ÖTÍ ² ÍvÍ Î Ð4Í Î ä3Ñ Î|± é|Ъâ]Í Î åOÍIÏ Ï$ÑMÖTÍÐ4ÍvâjÑ5Ð�ä#Ï]Ð�é�Ö ÑMæ×Í,¸BÕ�æ#ÍÖ.ÔAÐ Ì<± Í Ó Ï�Í Î Ï�Ñ0Ö ÑMÖTÍÌ ´ ± Ъâ Ñ5Öjæ|æ&ÏAÏ�Ö Õ ä3Ñ5ÍIä:Ñ Î Öjæ#ÑyÏ�ä�ÑyÏ Ï$Ívâ Ö Ì ÖjÑ5Ð Î å±Ð Î Ï�ÑyÏ$Ö Í Î Ö0´�Ñ ÌIÎ ä Í Ü ÍÃå±Ö Ñ�ÖTÍ�´MÑuâ ÍIÏ$ÑyÏ�Ö�Ï$Ö Ì â0Ö Ì ÖjÑ5Ð Î ¸

% Î é|Ð�â�æ Ì ÖjÑ5Ð Î é|âjÐPæ ë ² Í#´5Ð<Ô�ìEÖjæ#Í�Ï å<æ#ÍIä3Õb´5ÍvâRÐ*â Ð<Ö3Ñ�ä3ÍIÏQæ Ì â<ä�Ô Ì âjÍ Ó Ï3Ð4ÍIå±Ñ ß å�¯ Î Ð<Ô?´5ÍÃä ± Í�Ð�é�Ñ Î ä3Ñ�Ö3Ñ�ä ÓÕ Ì ´�åOÐPæ�Ð4Ð Î Í Î ÖöÏ Ì ´0Ð Î|± Ö æ#Í×%��P×âÐ Ì Ö æ�¸�Õ�æ#Ñ�ÏEä�ÑyÏ Ï$Ívâ Ö Ì ÖjÑ5Ð Î é|Ð�å±Õ4Ï$ÍIÏEÐ Î Ïjåµæ*ÍIä3Õ|´0Ívâ<ÏÖjæ Ì ÖYÕ4Ï$Í:ä�ÑyÏ3¯ä3âjÑMÖTÍCå±Ð Î�ßH± Õ#â Ì ÖjÑ5Ð Î ÌIÎ ä Ï$Ö Ì Ö Í?Ñ Î é|Ð�â�æ Ì ÖjÑ5Ð Î ¸dò?ÍÃåµæ ÌIÎ Ñyå Ì ´?Ð4ÐTÏ$Ñ5Ö Ñ0Ð Î Ñ Î|± ä3Í�´ Ì Ñ*ÏøÐ�é|ÖjÍ Î ä3Ð\æ:Ñ Î Ì Ö Íä3Ñ�Ï3¯�â Í5ÏòÕ#ÍÃÏ�ÖuÏ�Ívâ�Ö3Ñ�å±ÍVÖ Ñ�æ:ÍIÏOá Ì�Î ä�Ï å<æ#ÍIä3Õ|´0Ñ Î|± Ì ´ ± Ð�âjÑ5Ö æbæ&Ï�Ö æ Ì Öøâ ÍÃä3Õ4å±Í�Ö æ#ÍÃÏ�Í"æ:ÍIå<æ Ì�Î Ñ�å Ì ´�ä3Í�´ Ì Ñ#Ïâ ÍÃÏ�Õ|´0ÖøÑ Î Ï�Õ|Ð4ÍvâjÑ5Ð�âzÐ4Ívâ�é|Ъâ0æ ÌIÎ å±Í,¸ ½ ´ ± Ð�âjÑ5Ö æbæ&ÏYä3ÍIÏ�Ñ ±�Î ÍÃä Ö Ð�æ:Ñ Î Ñ�æ:Ñ:ávÍVÏ$ÍvÍ�¯úÖ Ñ�æ:ÍIÏâjÍ<ÏòÕ*Ñ5â Í"´5Ñ0Ö Ö�´5Íä3Ñ�Ï3¯ Ó Ï.Ð�ÍÃå±Ñ ß å�¯ Î Ð<Ô?´5ÍIä ± ÍTáQâjÍ�´MÑ�Ñ Îb± Ð Î Ö æ*Í[é Ì å±ÖYÖjæ Ì Ö Ì ä jÌ å±Í Î Ö�´5Ð ± Ñ�å Ì ´ ² ´5Ð�å�¯#Ï Ì â Í:Õ4Ï$Õ Ì ´�´MÑ�Ð#æ�Ñ*Ï�Ñ Óå Ì ´M´MÑ Ì ä jÌ å±Í Î Ö#¸ ½ ´ ± Ð�âjÑ5Öjæ|æ&Ï�ä3ÍIÏ$Ñ ±ªÎ ÍIäEÖjÐ�â ÍÃä3Õ4å±Íüå±ÐPæ ² Ñ Î ÍIäYÏ�ÍvÍ�¯ ÌIÎ äøâ ÐªÖ Ì ÖjÑ5Ð Î4Ì ´H´ Ì Ö Í Î å±Ñ5ÍIÏ�Õ Ï�Õ Ì ´M´MÑÐ�Õ*Ö0Ð4Ívâ�é|Ъâ0æ Ï�ÍZÍ�¯ Ó â ÍÃä3Õ4å±Ñ Î|±�Ì ´ ± Ð�âjÑ5Öjæ|æ&Ï±á ² Õ#ÖsÖ æ*Í�Ñ�â Í5ÏòÕ#Ñ0â Í Ì åZå±Õ#â Ì Ö Í�´5Ð ± Ñyå Ì ´ Ó Ö Ð Ó Ð#æ�Ñ*Ï�Ñyå Ì ´�ä Ì Ö Ì æ Ì Ð Ó

ê ô\Ì

Page 207: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô<Í

Ð#Ñ Î|± ÏOá#Ï�ÍZÍ�¯:åOÕ#â0ÖTÍIÏOáTæ#Í Ì ä×Ï3Ô�Ñ5Ööåµæ×Ö ÑMæ×ÍIϱáTåOÐPæ�æ ÌIÎ ä Ì�Î ä åOÐPæ�Ð|´0ÍvÖ Ñ0Ð Î Ð<ÖTÍvâjæ#Í Ì ä*ϱáTâ ÐªÖ Ì ÖjÑ5Ð Î Ï.Ð4ÍvÍIä#ÏOáÌ�Î ä Ì åOÖ Õ Ì Ö Ð�â�Ð4ÐTÏ$Ñ5Ö Ñ0Ð Î ÏÞ¸

½ÎúÌT±\± âjÍIÏ Ï$ÑMÖTÍ�Ï å<æ#ÍIä�Õ|´5Ívâ�å Ì�Î�Ì ´yÏ$Ð:Í Î Ð|´5ЪÑ5Ö�Ñ Î é|Ъâ0æ Ì Ö Ñ0Ð Î âjÍ�´ Ì Ö ÍIä&Ö Ð&Ö æ*ÍøÐPÐ4Ívâ Ì ÖjÑ5Ð Î�Ì�Î ä Ï$Ö Ì ÖjÍÐ�éAÖjæ#ÍøÐ Î#Ó�² Ð Ì â<äúä Ì Ö Ì å Ì åµæ*Í÷é|ÐªÕ Î ä?Ñ Î�Ì æ:Ð�ä�Ívâ Î ä3Ñ�Ï3¯Cä3â Ñ�ÖTÍ,¸ ÔAÌ åµæ#ÍÃä?ä Ì Ö Ì�² ´0Ð�åj¯*Ï Ì â Í Ì åvåOÍIÏ Ï$ÍIäé Ì â?æ×Ð�â ÍhÏTÕ#Ñyå�¯!´�ÑøÖjæ Ì�Î ² ´0Ð�åj¯*Ï�âjÍ<ÏòÕ*Ñ5â Ñ Î|± æ:ÍIä3Ñ ÌYÌ åvå±ÍÃÏ Ïl¸8¼�å<æ#ÍIä3Õ|´0Ñ Î|± Ì ´ ± Ð�âjÑ5Öjæ|æ&Ï]ä3ÍIÏ$Ñ ±�Î ÍIä[Ö ÐVÕ*Ö Ñ Ó´5Ñ�ávÍYÐ Î#Ó ² Ð Ì â<äûå Ì å<æ#ÍuÑ Î é|Ъâ0æ Ì Ö Ñ5Ð Î Ö.Ñ�Ð#Ñyå Ì ´M´�Ñ�Ð#â Ð�ä�Õ4å±Í�Ï�ÕbÐ�ÍZâ Ñ5ЪâuÐ4Ívâ�é|Ъâ0æ ÌIÎ å±Í,¸Y% Î Ð Ì â ÖjÑyå±Õ|´ Ì âZá�Öjæ#ÍÔ]Ó.ð ×�×hØ Ï å<æ#ÍIä�Õ|´5Ñ Î|±YÌ ´ ± Ъâ Ñ5Öjæ|æ�á<Ô�æ#Ñyå<æ Ì ´�Ô Ì Ñ*Ï�Ïjåµæ*ÍIä3Õ|´0ÍIÏ�Ð4Í Î ä3Ñ Î|± â Í<ÏTÕ#ÍIÏ$Ö<ÏQÑ Î ´0Ð ± Ñyå Ì ´M´MÑ Ì Ïjå±Í Î ä ÓÑ Îb± Ъâ<ä3ÍvâZá�Ñ Î Ö ÍZâ Ì åOÖ<Ï�Ô�Í�´�´,Ô�Ñ5Ö æ å±ÐPæ�æ:Ð Î Ð#âjͱé|ÍvÖ<å<æ#Ñ Î|± æ:ÍIå<æ Ì�Î ÑyÏ3æ×Ïl¸B×Öjæ#Ívâ�Ï å<æ#ÍIä3Õb´5Ñ Îb±�Ì ´ ± Ð�âjÑ5Ö æbæ&ϱáÏ�Õ åµæ Ì Ï�¼Tæ#Ъâ Ö ÍÃÏ�Ö�¼TÍZÍ�¯�Õ�ÑMæ:Í ³ Ñ5â<Ï$Ö ­ ¼b¼�Õ ³�® á å ÌIÎ�² Í�æ×Ð�ä3Ñ ß ÍÃä ÖjÐ:Ö Ì ¯TÍ ² ÍvÖjÖ Ívâ Ì ä!Ö Ì�Î Ö Ì<± ÍVÐ�éAÐ Î#Ó² Ð Ì â<ä:å Ì åµæ*ÍIÏ±á ² Õ#Ö]Ö æ#ÍóÏ�Ñ�æ�Ð|´5Ñ�å±Ñ5Ö(Ñ�Ð�é Ô]Ó�ð ×�×hØÓæ Ì ¯TÍIÏ�Ñ5Ö Ì�± ÐTÐ�ä×åµæ#ЪÑyå±Í�é|Ъâ8´5Ð<Ô Ó åOÐTÏ�ÖAä3Ñ�Ï3¯VâjÍ<ÏòÕ*ÍIÏ�ÖÏ å<æ#ÍIä�Õ|´5ÍvâAÑMæ�Ðb´5Í�æ�Í Î Ö Ì ÖjÑ5Ð Î Ïl¸Bò?Ð�âjÍuå±ÐPæ�Ðb´5Í Î�Ì ´ ± Ъâ Ñ0Ö æ|æ&Ï]Ö æ Ì ÖÍ Î Ð|´0Ð�Ñ0Ö�Ö æ*ÍVå Ì åµæ#ÍhÔ�æ#ÑM´0Í�â ÍIä�Õ4å±Ñ Îb±å±Ð\æ ² Ñ Î ÍIäYÏ�ÍZÍ�¯ ÌIÎ äcâjÐ�Ö Ì Ö Ñ0Ð Î4Ì ´H´ Ì ÖjÍ Î ålÑ ä3Í�´ Ì Ñ*Ï ­ Í,¸ ± ¸5á,¼�ç Ô Õ ³�® Ð#â Ð<Ö�Ñyä3Í�Öjæ#Í�æ#Ñ ± æ#ÍIÏ$Ö�Ð4Ívâ$é|Ð�â�æ Ì�Î åOÍ,¸ïqæ#Í Î Ï å<æ#ÍIä3Õb´5Ñ Îb± Öjæ#Í?Æ�à�k*íQl���Ö â Ì å±ÍTávé|Ð�â�Í Î#Ì æ�Ð|´0ÍTávÏ$Õ4åµæ Ì ´ ± Ð�âjÑ5Öjæ|æ&Ï�Ð#â Ð<Ö�Ñyä3Í8´5Ð<ÔAÍvâ�æ:Í ÌIÎ âjÍIÏ3Ð4Ð Î Ï�ÍÖ Ñ�æ:ÍIÏ Ì�Î ä Í<ÏTÕ#ÑMÖ Ì ´5Í Î ÖAÏ�Ö Ì â0Ö Ì ÖjÑ5Ð Î â ÍÃÏ�ÑyÏ$Ö ÌIÎ å±Í ­ å±Ð\æ�Ð Ì â ÍIäVÖ Ð×Ï�ÍvÍ#¯ Ó â ÍIä�Õ4å±Ñ Îb±VÌ ´ ± Ъâ Ñ5Öjæ|æ&Ï ® é|Ð�â�Öjâ Ì å±ÍÏ å Ì ´5Ñ Î|± é Ì åOÖ Ð�âöÏ�ÕbÐ ÖjÐ ê ¸ÊºVÐ�â?æ:Ъâ Í,¸

Õ�æ#ÑyÏ]ä3Ñ�Ï Ï$Ívâ Ö Ì Ö Ñ0Ð Î å±ÐPæ�Ð Ì âjÍIÏ Ì�Î Õbæ ² ÍvâsÐ�é�Ïjåµæ#ÍÃä3Õ|´5Ñ Î|±YÌ ´ ± Ъâ Ñ0Ö æ|æ&ÏBÐ#â Ð\Ð�ÐïÏ�ÍIä�Ñ Î Ð#âjÍ�Ö3Ñ0Ð�Õ4ÏRÔAÐ�â0¯Ì Ï�Ô�Í#´M´ Ì Ï�Ï�Ð\æ:Í Î Í#Ô Ö Ì â Ñ Ì ÖjÑ5Ð Î Ïl¸ ³ Ъâ�´0Ñ ± æ�Ö�Ô�Ъâ0¯�´5Ð Ì ä#ÏOá Ì ´M´�Ï å<æ#ÍIä�Õ|´5Ñ Î|±�Ì ´ ± Ð�âjÑ5Öjæ|æ&ÏpÐ#âjÐTÖ�Ñyä�Í�âjÐ�Õ ± æ|´MÑÍ<ÏTÕ#ÑMÖ Ì ´5Í Î Ö�Ð4Ívâ$é|Ð�â0æ Ì�Î å±Íw¸ ½ ÏøÖ æ#Í Ô�Ъâ0¯�´5Ð Ì äùÑ Î Ö Í Î Ï�Ñ5Ö.ÑúÑ Î åOâ Í Ì Ï�ÍIÏOá�Ö æ#Í Ð4Ívâ�é|Ъâ0æ ÌIÎ å±Í&ä�Ñ Ü Ívâ Í Î å±ÍIϲ ÍvÖ.Ô�ÍvÍ Î Ö æ#Í Ì ´ ± Ъâ Ñ0Ö æ|æ&Ï ± â Ð<Ô�¸d¼�å<æ#ÍIä3Õb´5ÍvâöÏEÕ4Ï$Ñ Î|±í³ Ñ5âöÏ�Ö Ô ÐPæ:Í ³ Ñ0â<Ï�Ö"¼TÍvâ�ÖTÍ ­;³�Ô�³ ¼ ® Ö.Ñ�Ð#Ñyå Ì ´M´�ÑÏ Ì Ö Õ#â Ì ÖjÍ Ì ä3Ñ�Ï3¯×Ï�Õ ² Ï.Ñ#Ï$Ö Í�æËÔ�Í�´�´ ² ͱé|Ъâ ÍYÖ æ*ÐTÏ�ÍYÕ4Ï$Ñ Î|±�Ì ´ ± Ð�â Ñ0Ö æ|æ Ï�ä3ÍIÏ$Ñ ±ªÎ ÍIä:Ö ÐVâjÍIä3Õ4å±Íhæ:ÍIå<æ Ì�Î Ñ�å Ì ´ä3Í�´ Ì Ñ#ÏÞ¸�Õ�æ#Í Ô]Ó.ð ×�×hØ Ïjåµæ*ÍIä3Õ|´0Ñ Î|±&Ì ´ ± Ð�â Ñ0Ö æ|æãæ Ì Ñ Î Ö Ì Ñ Î ÏÖjæ#Í�´0Ð<Ô�ÍIÏ$Ö�æ×Í Ì�Î âjÍIÏ3Ð4Ð Î Ï�Í:ÖjÑMæ:Í Ì�Î äâ ÍÃÏ3Ð4Ð Î Ï$ÍVÖ Ñ�æ:ÍuÖ Ì âjÑ Ì�Î å±Í Ì æ:Ð Î|± Öjæ#ÍVÏ$ÍvÍ�¯ Ó âjÍIä3Õ4åOÑ Î|±�Ì ´ ± Ъâ Ñ0Ö æ|æ&Ï�Ï$Ö Õ4ä�Ñ5ÍIäp¸A- Ì â Ñ Ì�Î Ö<Ï�Ð�é]Öjæ#Í�¼Tæ*Ð�â Ö ÓÍIÏ$ÖYçQÐTÏ$Ñ5ÖjÑ5Ð Î Ñ Î|± Õ�ÑMæ:Í ³ Ñ0â<Ï$Ö ­ ¼�ç8Õ ³�®�Ì ´ ± Ð�âjÑ5Ö æbæ�á|Ô�æ#Ñyå<æ?âjÍIä3Õ4åOÍIÏåOÐPæ ² Ñ Î ÍÃä Ï$ÍvÍ�¯ Ì�Î ä?â Ð�Ö Ì ÖjÑ5Ð Î Ì ´´ Ì Ö Í Î ålÑ�ä�Í�´ Ì Ñ*Ï±á ± Í Î Ívâ Ì ´M´�ÑuÐ#â Ð<Ö�Ñyä3Í�Ö æ#Í ² ÍIÏ�Ö�Ð4Ívâ$é|Ð�â�æ Ì�Î åOÍQé|Ð�âBæ:ÍIä3Ñ0Õ|æ Ó ÖjÐ Ó æ#Í Ì Ö!Ñ?ÔAÐ�â�¯!´0Ð Ì ä*Ïl¸���ÐTÔ ÓÍ�ÖTÍvâZá�¼�ç8Õ ³QÓ ²4Ì Ï$ÍIä Ì ´ ± Ъâ Ñ0Ö æ|æ&Ï�ä3Í ± â Ì ä3Í�´5ÍÃÏ Ï ± â Ì åOͱé|Õ|´M´�Ñ?Öjæ Ì�ÎûÔ]Ó�ð ×�×hØ é|ЪâøÖ æ*ÍVæ#Í Ì Ö3Ñ0ÍIÏ�ÖhÔ�Ð�â�¯ Ó´5Ð Ì ä#Ï ­ Ñ;¸ Íw¸5á�Ö æ*ÐTÏ�ÍúåÞ´5ÐTÏ$Í�Ö Ð Ï Ì Ö Õ#â Ì ÖjÑ5Ð ÎE® ¸ ÔAÌ åµæ#Í Ó Ï$Í Î Ï�Ñ0Ö Ñ�ÖTÍ�ÖTÍZâ<Ï�Ñ0Ð Î Ï�Ð�é"¼�ç8Õ ³ Õ Ï�Õ Ì ´M´MÑ�Ð#â Ð<Ö�Ñyä3ÍÖ æ*Í:æ#Ñ ± æ#ÍIÏ$Ö�Ð4Ívâ�é|Ъâ0æ ÌIÎ å±Í,¸ ½*± Í Ó Ï$Í Î Ï�Ñ0Ö Ñ�ÖTÍ�ÖTÍvâöÏ�Ñ0Ð Î ÏuÐ#âjÐTÖ�Ñyä�Í[Ñ Î å±â Í Ì Ï�ÍÃä~âjÍIÏ�Ñ�Ï�Ö ÌIÎ å±Í:ÖjÐ�Ï$Ö Ì â�Ö Ì Ö Ñ0Рέ Ñ(¸ Í,¸0áR´5Ð<Ô�ÍZâ:â ÍIÏ.Ð4Ð Î Ï$Í ÖjÑMæ:Í Ö Ì âjÑ Ì�Î å±Í ® ¸ Ô ÐPæ ² Ñ Î Ñ Î|± å Ì å<æ#Í Ó Ï�Í Î Ï�Ñ5ÖjÑMÖTÍ�¼�ç8Õ ³ Ô�Ñ5Ö æ Ì<± Í Ó Ï�Í Î Ï�Ñ0Ö ÑMÖTͼ�ç8Õ ³ Ð*â Ð�ä3Õ4åOÍIÏ Ì â Ð ² Õ4Ï$Ö&Ï å<æ#ÍIä3Õb´5Ñ Îb±úÌ ´ ± Ð�âjÑ5Ö æbæ Ö æ Ì Ö�Ð4Ívâ$é|Ð�â�æ&Ï�Ô�Í�´�´ Ì å±âjÐTÏjÏ Ì Ô�Ñyä3ÍCâ ÌIÎ|± ÍCÐ�éÔ�Ъâ0¯�´5Ð Ì ä#ÏÞ¸

¼TÍ�ÖTÍvâ Ì ´�Ïjåµæ#ÍÃä3Õ|´5Ñ Î|±�Ì ´ ± Ð�âjÑ5Ö æbæ ÐPÐ*Ö ÑMæ×ÑMá Ì Ö Ñ5Ð Î ÏøÍ Î Ð|´5ЪÑ5ÖVÖjæ#Í�Ð#âjÍIÏ�Í Î å±Í?ÐIé Ï�Í<ÏTÕ#Í Î Ö Ñ Ì ´�ä3Ñ�Ï3¯ûâ Í ÓÏTÕ#ÍIÏ�ÖöÏ�Ñ Î âjÍ Ì ´ Ó ÔAÐ�â�´yä�ÔAÐ�â0¯�´5Ð Ì ä#ÏÞ¸�ïqæ*Í Î&Ì æ#ÐïÏ�Ö Ó ²4Ì Ï�ÍIä�Ïjåµæ#ÍÃä3Õ|´5ÍZâ�åOÐ Î å Ì Ö Í Î Ì Ö ÍÃÏæ[Õ|´0Ö Ñ�Ð|´5ÍüÏ�Í<ÏTÕ#Í Î#ÓÖ Ñ Ì ´4â Í5ÏòÕ#ÍÃÏ�Ö<Ï]Ñ Î Ö ÐYé|Í�Ô�ÍvâZáP´ Ì â ± Ívâ�âjÍ<ÏòÕ*ÍIÏ�Ööϱá3Ñ0Ö]â ÍIä3Õ å±ÍIÏ�Ö æ#ÍóÖ Ð�Ö Ì ´ â Í<ÏTÕ#ÍIÏ$ÖÐ#âjÐ�å±ÍIÏ Ï$Ñ Î|± Ð<ÖTÍvâ æ#Í Ì ä Ì�Î ä² ÍvÖ ÖjÍvâ�Õ#ÖjÑM´0ÑMávÍIÏ�Ö æ*ÍVÖ Ì â ± ÍvÖ÷ä3ÑyÏ.¯��¢ÏÐ Î#Ó ² Ð Ì â<äùå Ì åµæ*Í,¸ ³ Ъâ�Ö æ#Í�ÂoÃ����Tà�Öjâ Ì åOÍTápÔ�æ#Ñ�åµæúå±Ð Î Ö Ì Ñ Î ÏÐ�åvå ÌIÓÏ�Ñ0Ð Î4Ì ´ ² Õ*â<Ï�ÖöÏEÐIé�æ#Ñ ± æ|´�ÑúÏ�Í<ÏTÕ#Í Î Ö Ñ Ì ´�âjÍ Ì ä#ÏOá�å±Ð Î å Ì Ö Í Î4Ì Ö Ñ Î|± âjÍ Ì ä�â Í<ÏTÕ#ÍIÏ$Ö<Ï Ì ÖuÖ æ#Í�æ#ÐïÏ�ÖVä�ÍIå±â Í Ì Ï�ÍÃÏæ:Í ÌIÎ âjÍIÏ3Ð4Ð Î Ï�Í�Ö ÑMæ×ÍIÏ ² Ñ�¿\À5ä|¹5À}Ò ­ é|Ъâ Ì ´�´ Ì ´ ± Ð�âjÑ5Öjæ|æ&Ï�Í Î åOÍ�Ð#Ö ³�Ô�³ ¼ ®�Ì Ö Ì Ö â Ì å±Í�Ï å Ì ´5Ñ Î|± é Ì å±Ö ЪâÐ�é ê ¸ÊÄPº�¸ ½ ´5Ö ÍZâ Î4Ì Ö Í�´�ÑTá Ì Ï å<æ#ÍIä3Õ|´0Ívâ�å ÌIÎ ÑMæ�Ð#âjÐ<ÖTÍ�Ð4Ívâ$é|Ð�â�æ Ì�Î åOÍ ² Ñ Í Î Ð|´0Ñyå±Ñ0Ö0´�Ñ:Ïjåµæ#ÍÃä3Õ|´5Ñ Î|± Ï�Í<ÏTÕ#Í Î#ÓÖ Ñ Ì ´Aâ Í<ÏTÕ#ÍIÏ$Ö<ÏEÑ Î ´5Ð ± Ñ�å Ì ´�´MÑ Ì Ï åOÍ Î ä3Ñ Î|± Ð�âöä3Ívâ�¸�Õ�æ#Ñ�ÏøÐPÐ#ÖjÑMæ:Ñ�á Ì ÖjÑ5Ð ÎúÌ ´yÏ$Ð�æ Ì ¯TÍIÏ ² ÍvÖjÖ ÍvâVÕ Ï�Í:ÐIé�Öjæ#ÍÐ Î*Ó�² Ð Ì â<ä&å Ì åµæ#Íïá ² Õ#Ö]Ñ5ÖAå ÌIÎ ä�Í ± â Ì ä3Í�Ð4Ívâ�é|Ъâ0æ ÌIÎ å±Í?Ô�æ#Í Î Ï å<æ#ÍIä�Õ|´5Ñ Î|± Ï�Í<ÏTÕ#Í Î Ö Ñ Ì ´*Ï�Ö âjÍ Ì æ ÏQÐ�éBÔ�âjÑ5Ö Íâ Í5ÏòÕ#ÍÃÏ�Ö<Ï�é|Ð�âYä3Ñ�Ï3¯*Ï*Ô�Ñ5Öjæ#Ð�Õ*Ö�Ö æ#Í Ì<² ÑM´0Ñ5Ö.Ñ&Ö Ð�Ð*â Í ² Õ Ü ÍZâuÔ�â Ñ0Ö ÍVâ Í5ÏòÕ#ÍÃÏ�Öóä Ì Ö Ì ¸ ³ Ð�â÷ä3ÑyÏ.¯#Ï*Ô�Ñ0Ö æ�Ô�âjÑ5Ö ÍÐ#âjÍ ² Õ Ü ÍvâjÑ Î|± á3Ï$Í<ÏTÕ#Í Î Ö Ñ Ì ´�Ï å<æ#ÍIä3Õb´5Ñ Îb± Ð�éEÔ�â Ñ0Ö ÍIÏ ± Í Î ÍZâ Ì ´�´MÑzÐ#â Ð<Ö�Ñyä3ÍIÏ Ì æ Ì â ± Ñ Î4Ì ´�â ÍIä�Õ4å±Ö Ñ0Ð Î Ñ Î æ:Í Ì�Îâ ÍÃÏ3Ð4Ð Î Ï$ÍøÖjÑMæ:ÍIÏÞ¸

% ÎùÌ å±Í Î Ö â Ì ´0ÑMávÍIäCÏ å<æ#ÍIä3Õb´5Ívâ�ÑMæ�Ðb´5Í�æ�Í Î Ö Ì ÖjÑ5Ð Î á#Ð Î ´�Ñ�Ð Î Í�Í Î Ö Ñ0Ö3Ñ Ì ´5Ð Îb± Öjæ#Í×%��\×âÐ Ì Ö æ Ì å±ÖjÑMÖTÍ�´�Ñâ ÍZÐ�â<ä�Ívâ<Ï*Ð4Í Î ä3Ñ Î|± âjÍ<ÏòÕ*ÍIÏ�ÖöÏl¸�×Öjæ#Ívâ�Í Î ÖjÑ5Ö Ñ0ÍIÏÐ Ì â Ö Ñ�å±ÑMÐ Ì Ö ÍVÑ Î ä3ÑyÏ.¯CÏ å<æ#ÍIä3Õ|´0Ñ Î|± Ð Î ´�Ñ ² Ñ?Í Î Ö â Ì å±ÖjÑ Î|±Ì�Î ä�Ð Ì Ï Ï$Ñ Î|± Õ4Ï�ͱé|Õb´�Ñ Î é|Ъâ0æ Ì Ö Ñ0Ð Î Ö ÐûÖjæ#Í Ì å±ÖjÑMÖTÍúÏjåµæ#ÍÃä3Õ|´5ÍZâ�¸üÕ�æ#Í æ*ÐTÏ�Ö ÌIÎ ä{Ö æ*Íúä3ÑyÏ.¯ Ì âjÍ Ö.ÔAÐ

Page 208: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô\º

Ð ² Ö�Ñ5Ð�Õ Ï�´0Ð�å Ì ÖjÑ5Ð Î Ï é|Ъâ Ì å±Í Î Ö â Ì ´5Ñ�ávÍIä Ï å<æ#ÍIä3Õ|´0Ívâvá Ì Ï Í Ì åµæ Ð4ÐTÏ Ï$ÍIÏ Ï$ÍIÏ Ì Ï�Ñ ±�Î Ñ ß å Ì�Î Ö�ÏòÕ Ì�Î Ö Ñ5Ö.Ñ Ð�éÑ Î é|Ð�â0æ Ì Ö Ñ0Ð Î Õ4Ï$ͱé|Õ|´�Ö ÐûÏjåµæ#ÍÃä3Õ|´5Ñ Î|±úÌ åOÖ ÑMÖ�Ñ5ÖjÑ5ÍIÏÞ¸q�ÐïÏ�Ö Ó ²4Ì Ï�ÍIäqÏjåµæ#ÍÃä3Õ|´5ÍZâ<ÏVæ Ì ÖTÍ Öjæ#Í Ì ä!Ö Ì�Î Ö Ì<± ÍúÐ�éÏ�Í5ÏòÕ#Í Î ÖjÑ Ì ´�â Í5ÏòÕ#ÍÃÏ�Ö�å±Ð Î å Ì Ö Í Î4Ì ÖjÑ5Ð Î ¸8Õ�æ#Í�Ñ Ì ´yÏ$ÐEæ Ì ÖTÍ ­ ÍIÏjÏ�Í Î Ö Ñ Ì ´�´MÑ ® Õ Î�² Ð�Õ Î ä3ÍIä"ÏòÕ#ÍZÕ#ÍIÏ�é|Ð�â]æ#ÐP´�ä3Ñ Îb±â Í5ÏòÕ#ÍÃÏ�Ö<ÏOá Ì ´M´0Ð<Ô�Ñ Î|±&Ì ´M´RÐ4Í Î ä3Ñ Î|± â Í<ÏTÕ#ÍIÏ$Ö<ÏÖjÐ ² Í×å±Ð Î Ï�Ñ�ä3Ívâ ÍÃä é|Ð�âuÏ�Ívâ�Ö3Ñ�å±Í,¸�»�ÑyÏ3¯ Ó ²4Ì Ï$ÍIä Ïjåµæ*ÍIä3Õ|´0Ívâ<Ïæ Ì ÖTÍ�´5Ñ�æ:Ñ5ÖjÍIä[åOÐPæ�æ ÌIÎ ä�ÏTÕ#ÍvÕ#Íuå Ì Ð Ì åOÑ5Ö.ÑTá ² Õ#Ö�Ö æ*Í�Ñ�æ Ì<Î Ñ�æ:Ñ:ávÍÑ Î ÖjÍvâ Ó â Í5ÏòÕ#ÍÃÏ�Ö�åOÐ Î å±Õ*â â Í Î ålÑ Ì ÖÖjæ#Íä3Ñ�Ï3¯ Ì�Î ä æ Ì ÖTÍ ² ÍvÖ ÖjÍvâ Ì åvå±ÍIÏjÏEÖjÐ�ä3Ñ�Ï3¯�å±Ð Î!ße± Õ#â Ì Ö Ñ0Ð Î Ì�Î äùÏ�Ö Ì Ö Í×Ñ Î é|Ъâ0æ Ì Ö Ñ5Ð Î ¸ ½ ´�Ï�Ð#á]ä�ÑyÏ3¯ Ó ²4Ì Ï$ÍIäÏ å<æ#ÍIä�Õ|´5ÍvâöÏ Ì â Í ² ÍvÖ ÖjÍvâ�Ï�Õ#Ñ0Ö ÍIäùÖjÐ Í Î Ð|´0Ð�Ñ5ÖuÖ æ#Í&Ñ Î å±â Í Ì Ï�Ñ Î|± å±Ð\æ�Ð#Õ#Ö Ì Ö Ñ0Ð ÎûÌIÎ äYæ×Í�æ:Ð�â�Ñ?âjÍIÏ�ЪÕ#â<å±ÍÃÏÑ Î ål´5Õ4ä�ÍIä�Ô�Ñ5Öjæ æ:Ð�ä3Ívâ Î ä�ÑyÏ3¯ ä3â Ñ�ÖTÍYå±ÐPæ�Ð�Ð Î Í Î Ö<ÏÞ¸

�ÐTÏ$Ö Ó ²4Ì Ï$ÍIäùÏjåµæ#ÍÃä3Õ|´5ÍZâ<ÏYå Ì�Î Í Î Ð|´5ЪÑ5Ö�Ñ Î ÖjÍvâ Ó â Í5ÏòÕ#ÍÃÏ�ÖYå±Ð Î å±Õ#âjâ Í Î ålÑ ² Ñ�Õ4Ï�Ñ Î|±�³�Ô�³ ¼ å±ÐPæ�æ Ì�Î ä ÓÏTÕ#ÍvÕ#ÍIä�ä3Ñ�Ï3¯*Ïl¸¼Tæ#Ъâ Ö�å±Ð\æ�æ ÌIÎ ä�ÏòÕ*ÍvÕ#Í�´5Í Î|± Ö æ4Ï8Ð#â Ð<Ö�Ñyä3ÍóÖ æ#Í ² ÍIÏ�Ö?Ð4Ívâ$é|Ð�â0æ Ì�Î å±Í��}´0Ð Î|± Ívâ�Ð Î#Ó ² Ð Ì âöäÏTÕ#ÍvÕ#ÍIÏ�â ÍIä3Õ å±Í Ì æ#ÐïÏ�Ö Ó�²4Ì Ï�ÍIä�Ï å<æ#ÍIä3Õ|´0Ívâv�¢Ï��4Í Î Ñ ² ÑM´5Ñ0Ö.Ñ:Ö ÐCä!Ñ Î4Ì æ×Ñyå Ì ´M´MÑ&âjÍvÐ�âöä3Ívâ�âjÍ<ÏòÕ*ÍIÏ�ÖöÏl¸�× Î Öjæ#ÍÐ�Öjæ#Ívâ]æ ÌIÎ ä�á3Í Î Ð4ÍvâjÑMæ:Í Î Ö<Ï�ä�â ÑMÖTÍ Î�² ÑVÖjæ#Í�é|Õ|´M´ Ï.Ñ#Ï$Ö Í�æ Ö â Ì å±ÍIÏ�Ñ Î ä3Ñyå Ì Ö Í�Öjæ Ì Öüä3ÑyÏ.¯Vå±Ð\æ�æ Ì�Î ä�ÏTÕ#ÍvÕ#Í ÓÑ Îb± æ Ì Ñ Î ÐªÖ ² Í Ì ä!Ö�ÑyÏ Ì<² ´5Í�é|Ъâ�æ#ÐTÏ$Ö Ó ²4Ì Ï$ÍIä�Ï å<æ#ÍIä3Õb´5ÍvâöÏ�Ö æ Ì Ö�Õ4Ï$ÍEâjÍ<ÏTÕ#ÍIÏ�Ö?Ð*â Ñ5Ъâ Ñ0Ö3ÑVÑ Î é|Ð�â�æ Ì ÖjÑ5Ð Î ¸]%¤é´5Ð<ÔâÐ#âjÑ5Ъâ Ñ5Ö.Ñ�âjÍ<ÏòÕ*ÍIÏ�ÖöÏ Ì âjÍ:ÑyÏjÏ�Õ#ÍÃä Ö Ð Ì�³�Ô�³ ¼ å±Ð\æ�æ Ì�Î ä Ó ÏTÕ#ÍvÕ*ÍIä�ä3ÑyÏ.¯�á Ì æ#ÐTÏ$Ö Ó ²4Ì Ï$ÍIäûÏ å<æ#ÍIä3Õb´5Ívâå ÌIÎ#Î Ð�Öóå<æ Ì�Î|± ÍYÖ æ#ÍYÐ�âöä3Ívâ�ÐIéAÏ�Ívâ�Ö3Ñ�å±ÍuÔ�æ#Í Î Ï$Õ ² Ï$Í<ÏòÕ*Í Î Ö�æ*Ñ ± æ Ð#âjÑ5Ъâ Ñ5Ö.Ñ:âjÍ<ÏTÕ#ÍIÏ�ÖöÏ Ì â â Ñ�ÖTÍ,¸

½ ´5Öjæ#Ð�Õ ± æ�Ö æ#Í�ÐPÐ#ÖjÑMæ Ì ´|´5Ð�å Ì Ö Ñ0Ð Î é|Ð�â Ì å±Í Î Ö â Ì ´5Ñ�ávÍIäuÏ å<æ#ÍIä3Õ|´0Ívâ�Ñ�Ï�ÔAÐ�â�¯!´0Ð Ì ä Ó Ï.Ð�ÍÃå±Ñ ß åªá3Ïjåµæ*ÍIä3Õ|´0Ñ Î|±Ì ´ ± Ъâ Ñ5Öjæ|æ&Ï�Õ4Ï�Ñ Î|± âjÍ<ÏòÕ*ÍIÏ�Ö�Ð#â Ñ0Ð�âjÑ5Ö.Ñ&Ñ Î é|Ъâ0æ Ì Ö Ñ5Ð Î Ô�Ð�â�¯ ² ÍIÏ$Ö�Ñ é]Ñ�æ�Ð|´0Í�æ[Í Î ÖjÍvä Ì Ö�Ö æ*ÍVæ#ÐTÏ$Ö ­ Õ Î ´5ÍIÏjÏÖ æ*Í�Ô�Ъâ0¯�´5Ð Ì ä Ñ�Ï�ÖTÍZâ0Ñ�´0Ñ ± æ�Ö ® ¸*×�Ö æ#ÍZâ0Ô�ÑyÏ$ÍTáHÔ�æ#Í Î�Ì ä3Ñ�Ï3¯ ��Ï�Ð Î#Ó ² Ð Ì âöä åOÐPæ�æ ÌIÎ ä�ÏTÕ#ÍvÕ#Íuâ Í Ì åµæ*ÍIÏ�Ñ5ÖöÏæ Ì<Î Ñ�æ[Õ|æË´5Í Î|± Ö æ�á�Ï�Õ ² Ï�Í<ÏTÕ#Í Î ÖYâ Í<ÏTÕ#ÍIÏ$Ö<Ï Ì â Í Î Ð�Ö å±Ð Î Ï�Ñyä�Ívâ ÍIä�é|Ð�âVÏ$Ívâ0Ö�ÑyåOÍ ­ Õ Î Ö Ñ�´]Ï3Ð Ì å±Í ² ÍIå±Ð\æ:ÍIÏÌ Ö Ì ÑM´ ÌT² ´0Í�Ñ Î Ö æ#Í�Ð Î#Ó ² Ð Ì âöä�ÏTÕ#ÍvÕ*Í ® ¸�%¤éuæ#Ñ ± æÓÐ#â Ñ0Ð�âjÑ5Ö.Ñûâ Í<ÏTÕ#ÍIÏ$Ö<Ï&å Ì�Î*Î Ð�ÖCâ Í Ì åµæqÖjæ#Íùä�ÑyÏ3¯ Ó ²4Ì Ï$ÍIäÏ å<æ#ÍIä�Õ|´5ÍvâZá3Ð<ÖTÍvâ Ì ´M´ Ï.Ñ#Ï$Ö Í�æ�Ð4Ívâ$é|Ð�â�æ Ì�Î åOÍYÏ�Õ Ü ÍvâöÏl¸

% ÎúÌ ä3ÑyÏ$Ö âjÑ ² Õ#ÖjÍIä?Ïjåµæ*ÍIä3Õ|´0ÍvâÑ�æ�Ð|´0Í�æ[Í Î Ö Ì ÖjÑ5Ð Î á3Ö.Ô�Ð×Ð�âuæ:Ъâ ÍuÍ Î ÖjÑ5ÖjÑ5ÍIÏ Ì ´5Ð Îb± Öjæ#ÍV%��\×ÚÐ Ì Ö æ�å±Ð ÓÐPÐ4Ívâ Ì ÖjÑMÖTÍ�´�Ñ:â ÍvЪâ<ä3ÍZâYä3ÑyÏ.¯&â Í<ÏTÕ#ÍIÏ$Ö<Ïl¸hî Ì å<æúå±ÐPæ�Ð4Ð Î Í Î Ö�Ïjåµæ#ÍÃä3Õ|´5ÍZâ�Í Î Ðb´5Ð�Ñ0Ö<Ï�ä3Ñ Ü ÍvâjÍ Î ÖÑ Î é|Ð�â�æ Ì ÖjÑ5Ð ÎÖ Ð Ì åµæ*Ñ5Í�ÖTÍ×Ï3Ð4ÍIå±Ñ ß å:Ïjåµæ#ÍÃä3Õ|´5Ñ Î|±�± Ð Ì ´yÏl¸mÕ�æ*ÑyÏVä3Ñ�Ï Ï�ÍZâ Ö Ì Ö Ñ0Ð Î Í Î*Ì æ:Ñ Î ÍIÏYä3ÑyÏ$Ö âjÑ ² Õ#ÖjÍIäùÏjåµæ#ÍÃä3Õ|´5ÍZâøÑMæ ÓÐ|´0Í�æ:Í Î Ö Ì Ö Ñ5Ð Î Ï�Öjæ Ì Ö�Õ4Ï$Íøæ#ÐïÏ�Ö Ó ²4Ì Ï�ÍIä�Ïjåµæ#ÍÃä3Õ|´5ÍZâ<Ï�Ñ Î å±Ð Î� Õ Î å±ÖjÑ5Ð Î Ô�Ñ0Ö æ�ä�ÑyÏ3¯ Ó ²4Ì Ï$ÍIä?Ïjåµæ#ÍÃä3Õ|´5ÍZâ<Ïl¸A% Îæ:ÐïÏ�ÖYå Ì Ï�ÍIÏOá Ì Ô�Í#´M´ Ó ä3ÍIÏ$Ñ ±ªÎ ÍIä?ä�ÑyÏ�Öjâ Ñ ² Õ#Ö ÍÃä�Ï å<æ#ÍIä3Õ|´0Ívâ�ЪÕ#Ö0Ð4Ívâ$é|Ð�â0æ Ï Ì å±Í Î Öjâ Ì ´0ÑMávÍÃä?Ï å<æ#ÍIä�Õ|´5Ívâ�Ô�Ñ5ÖjæÍ<ÏTÕ#ÑMÖ Ì ´5Í Î Ö�âjÍIÏ�ЪÕ#â<å±ÍÃÏl¸

% Î:Ì ä#ä3Ñ5ÖjÑ5Ð Î Ö ÐYÖ æ*Í*Ð4Ívâ$é|Ð�â0æ Ì�Î å±Í Ì ä!Ö Ì�Î Ö Ì<± ÍTá4ä3Ñ�Ï�Öjâ Ñ ² Õ#Ö ÍIäVÏjåµæ*ÍIä3Õ|´0Ñ Î|± Ð#âjÐTÖ�Ñyä�ÍIÏ]å±ÐTÏ$Ö ÌIÎ ä:å±Ð\æ ÓÐ|´0Í Î Ñ0Ö.Ñ ² Í Î Í ß ÖöÏl¸ ½*±\± âjÍIÏ Ï$ÑMÖTÍ?æ*ÐTÏ�Ö Ó�² Ì Ï�ÍÃä{å±Í Î Öjâ Ì ´0ÑMávÍÃä Ïjåµæ*ÍIä3Õ|´0Ívâ<ÏøâjÍ<ÏòÕ*Ñ5â ÍCÖ æ#ÍCÍ Î Ö â Ì å±Ö Ñ0Ð Î Ì�Î äå±Ð\æ�æ[Õ Î Ñyå Ì ÖjÑ5Ð Î ÐIé Ì ´ Ì â ± ÍzÏòÕ Ì�Î Ö Ñ5Ö.ÑVÐIé]ä3Ñ�Ï3¯ Ó Ï.Ð4ÍIå±Ñ ß å�å±Ð Î�ßH± Õ#â Ì ÖjÑ5Ð Î Ì�Î ä&Ï$Ö Ì ÖjÍYÑ Î é|Ъâ0æ Ì Ö Ñ5Ð Î ¸R»�ÑyÏ ÓÖ âjÑ ² Õ*Ö ÍIäCÏ å<æ#ÍIä3Õ|´0Ívâ<Ï�ä�Ð Î Ð�Öóâ Í<ÏTÕ#Ñ5âjÍYÖ æ#Ñ�Ï Ì ä#ä�Ñ5Ö Ñ0Ð Î4Ì ´�åOÐPæ�Ð|´0Í Î Ñ5Ö.ÑTá�Ï�Ñ Î å±ÍøÖjæ#ÍVä�ÑyÏ3¯ Ó ²4Ì Ï$ÍIä�Ï å<æ#ÍIä3Õb´ ÓÑ Îb± å±Ð\æ�Ð4Ð Î Í Î Ö�æ Ì ÏøÍ Ì Ï.Ñ Ì åvåOÍIÏ ÏYÖ Ð Ì ´M´Aä3Ñ�Ï3¯ Ó Ï.Ð�ÍÃå±Ñ ß åVä Ì Ö Ì ¸�»�ÑyÏ3¯ Ó ²4Ì Ï$ÍIäùå±Í Î Ö â Ì ´0ÑMávÍIä�Ïjåµæ*ÍIä3Õ|´0Ívâ<Ïå ÌIΠ² Í:æ Ì æ�Ð�ÍZâ ÍIä ² Ñ�´5Ñ�æ:Ñ5ÖjÍIä Ð Î#Ó ² Ð Ì âöäYæ:Í�æ×Ð�â0Ñ ÌIÎ äùå±Ð\æ�Ð#Õ#Ö Ì Ö Ñ0Ð Î âjÍIÏ�ЪÕ#â<åOÍIÏl¸C% Î Ð Ì âjÖ Ñ�å±Õ|´ Ì âváæ#Ñ ± æ�Ð*â Ñ5Ъâ Ñ0Ö3Ñ×â Í<ÏTÕ#ÍIÏ$Ö<Ïæ Ì Ñ ² Í ä3Í�´ Ì ÑTÍÃä Ì ÖÖjæ#ÍYæ#ÐTÏ$Ö�Ñ é�Ð Î*Ó�² Ð Ì â<ä�â Í<ÏTÕ#ÍIÏ$Ö�ÏòÕ*ÍvÕ#ÍIÏ Ì â ÍøÖjÐTÐ&Ï3æ Ì ´M´(¸»Ñ�Ï�Ö âjÑ ² Õ*Ö ÍIäúÏ å<æ#ÍIä3Õb´5Ñ Îb± å±Ð\æ�Ð4Ð Î Í Î Ö<ÏYå ÌIÎ å±ÐTÐ\Ð�ÍZâ Ì ÖjÍ&Ö Ð?âjÍIä3Õ4åOÍ[Öjæ#Í:ÑMæ�Ð Ì å±ÖóÐ�é ß4Î Ñ5ÖjÍ[Ð Î#Ó ² Ð Ì âöäå±Ð\æ�æ Ì�Î ä�ÏTÕ#ÍvÕ*ÍIÏl¸zÕ�æ#ÑyÏóå±ÐTÐPÐ4Ívâ Ì Ö Ñ0Ð Î å Ì�ÎúÌ åOÖ Õ Ì ´M´MÑCâ ÍIä�Õ4å±ÍVÖ æ*Í Ì æ:ÐªÕ Î Ö�Ð�éüÐ Î#Ó ² Ð Ì â<ä âjÍIÏ�ЪÕ#â<å±ÍÃÏâ Í5ÏòÕ#Ñ0â ÍIä?é|Ð�â ± ÐTÐ�ämÐ�ÍZâ�é|Ð�â�æ Ì�Î å±Í,¸ ³ ЪâøÍ Î*Ì æ�Ð|´5ÍTá�Ï�Í�ÖTÍvâ Ì ´]Ð�éóÖ æ*Í[âjÍ Ì ´ Ó ÔAÐ�â0´�ä Ö â Ì å±ÍÃÏEÕ4Ï$ÍIä Ñ Î Ö æ#Ñ�Ïä3Ñ�Ï Ï�ÍZâ Ö Ì Ö Ñ0Ð ÎûÌ â Í ² ÍIÏ$Ö�Ï å<æ#ÍIä3Õ|´0ÍIä ² Ñúä3Ñ�Ï�Öjâ Ñ ² Õ#Ö ÍIäúÑMæ�Ð|´0Í�æ�Í Î Ö Ì Ö Ñ5Ð Î ÏÕ4Ï$Ñ Î|± ä�ÑyÏ3¯*Ï�Ô�Ñ0Ö æùâjÍ�´ Ì Ö Ñ�ÖTÍ�´MÑÏ�æ*Ð�â Ö�Ð Î*Ó�² Ð Ì â<ä�å±Ð\æ�æ ÌIÎ ä�ÏTÕ#ÍvÕ*ÍIÏl¸

½ ÏÖjæ#Í�ä3Í�æ ÌIÎ ä#ÏÐ Î ä�ÑyÏ3¯ Ï�Õ ² Ï3Ñ*Ï�Ö Í#æ&Ï�Ñ Î å±âjÍ Ì Ï$ÍTá�ä3Ñ�Ï3¯?âjÍ<ÏTÕ#ÍIÏ�Ö÷Ï å<æ#ÍIä3Õ|´0Ñ Î|±"² ÍIå±Ð\æ:ÍIÏ Ì æ Ì� Ð�âé Ì åOÖ Ð�â�Ñ Î ä3ÍvÖ ÍZâ0æ:Ñ Î Ñ Î|± Ï.Ñ#Ï$Ö Í�æ Ð4Ívâ�é|Ъâ0æ ÌIÎ å±Í,¸ ½�Î Ñ�æ�Ð#âjÐPÐ4Ívâ0´�Ñ�ä3ÍIÏ$Ñ ±�Î ÍIä�Ð�â�ÑMæ�Ð|´5Í�æ�Í Î Ö ÍZä�Ï å<æ#ÍIä3Õb´5Ívâå ÌIÎ Í Ì Ï�ÑM´�Ñ ² Í]Ö æ#Í ² ÐªÖ Ö�´5Í Î ÍÃåj¯�Ñ ÎuÌ æ:ÍIä3Ñ0Õ|æ Ó Ð�âsæ#Í Ì Ö�ÑM´�Ñ Ó ´5Ð Ì ä3ÍIäóä3ÑyÏ.¯øÏ$Õ ² Ï.Ñ#Ï$Ö Í�æ�¸�Õ�æ#ÑyÏsä3ÑyÏjÏ�ÍvâjÖ Ì Ö Ñ5Ð ÎÐ#âjÐTÖ�Ñyä�ÍIÏ ± Õ*Ñyä3Í�´0Ñ Î ÍÃÏ�é|Ð�âuå±Ð\æ�Ð#Õ#ÖjÍvâ�Ï.Ñ#Ï$Ö Í�æ�Í Î|± Ñ Î ÍvÍvâöÏ�å±Ð Î å±Ívâ Î ÍIä�Ô�Ñ5Öjæ ² Õ#ÑM´�ä3Ñ Îb±?Ì<±P± â ÍIÏjÏ�ÑMÖTÍ�ä�ÑyÏ3¯â Í5ÏòÕ#ÍÃÏ�Ö�Ï å<æ#ÍIä�Õ|´5ÍvâöÏ�Ñ Î æ*Ñ ± æ Ó Ð4Ívâ$é|Ð�â0æ Ì�Î å±Í÷Ï3Ñ*Ï�Ö Í#æ&Ï�Õ4Ï$Ñ Î|± Ï�Ö Ì ÖjÍ Ó ÐIé Ó Öjæ#Í Ó.Ì âjÖYÏ�ÖjÐ�â Ì<± Í å±ÐPæ�Ð4Ð Î Í Î Ö<Ïl¸

Page 209: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô\¿

�&9 � \�F&N�FCU]B ! SVU��

Õ�æ#Í�Ô�Ъâ0¯&Ñ Î Ö æ*ÑyÏ�ä3Ñ�Ï Ï�ÍZâ Ö Ì Ö Ñ0Ð Î å Ì�Î ² ÍøÍ Î ÖjÍ Î ä3ÍIä�Ñ Î Ï�Í�ÖTÍZâ Ì ´ Ì âjÍ Ì ÏOã

" Õ�æ#Í×Í Ü ÍIå±Ö<ÏYÐ�é÷ä3ÑyÏ.¯ùä�â ÑMÖTÍ�Ö ÍÃåµæ Î ÐP´5Ð ± ÑúÐ Î Ï å<æ#ÍIä�Õ|´5Ñ Î|±CÌ å±ÖjÑMÖ�Ñ5Ö Ñ0ÍIÏuæ[Õ Ï�Ö ² Í&å±Ð Î Ö Ñ Î Õ Ì ´M´�Ñ�â Í ÓÍ�Ö Ì ´5Õ Ì Ö ÍIäp¸ ó ÐªÖ Ì Ö Ñ5Ð Î Ï.Ð�ÍZÍIä#Ï Ì�Î ä�æ:ÍIä3Ñ Ì ä3Í Î Ï�Ñ5ÖjÑ5ÍIÏ Ì â ÍAÑ Î å±âjÍ Ì Ï$Ñ Î|± ��Ï$ÍvÍ�¯�ÖjÑMæ:ÍÃÏ Ì âjÍ�ä3âjÐPÐ|Ð*Ñ Î|± �Ð4ÍvâjÑMÐ#æ#ÍZâ Ì ´ ² Õ4Ï�ÍÃÏ Ì âjÍ ± ÍvÖ ÖjÑ Î|± Ô�Ñ�ä3Ívâ ÌIÎ äcé Ì Ï$Ö Ívâ#� Ì�Î ä�ä3ÑyÏ.¯�Ð|´ Ì Ö ÖjÍvâAä3Ñ Ì æ:ÍvÖ ÍZâ<Ï Ì â ÍóÏ�æ*â Ñ Î ¯3Ñ Î|± ¸½ ÏVä�ÑyÏ3¯úÖ ÍÃåµæ Î ÐP´5Ð ± ÑùÑ�ÏøÍ Î Ð�ÍÃå±Ö ÍIäúÖ Ð�ÑMæ�Ð#â Ð<ÖTÍ×ä3â Ì æ Ì ÖjÑyå Ì ´M´MÑ�Ñ Î Ö æ*Í Î Í Î Ö�ä�ÍIå Ì ä�ÍTá]Ï�ÖjÕ4ä3Ñ5ÍÃÏÑ�ä3Í Î Ö Ñ é Ñ�Ñ Îb±?Ì ä#ä3Ñ0Ö Ñ5Ð Î4Ì ´üÏ å<æ#ÍIä3Õb´5Ñ Îb± ÑyÏjÏ�Õ#ÍÃÏEé|Ð�âøé|Õ#ÖjÕ#â Í:æ*Ñ ± æ Ó Ð4Ívâ$é|Ð�â0æ Ì�Î å±Í ä3ÑyÏ.¯ùÏ$Õ ² Ï3Ñ*Ï�ÖjÍ�æ&ÏÔ�Ñ�´M´ ² Í Î ÍvÍÃä3ÍIäp¸

" ³ Õ|´�´ Ó ¯ Î Ð<Ô?´0ÍIä ± Í÷Ï å<æ#ÍIä3Õ|´0Ñ Î|±�Ì ´ ± Ð�â Ñ0Ö æ|æ Ï Ì â ÍYÕ4Ï$Õ Ì ´�´MÑ ´5Ð�å Ì Ö ÍÃä Ì ÖÖjæ#ÍVä�ÑyÏ3¯ ä3â Ñ�ÖTÍTá#Ï$Ñ Î å±ÍYÖjæ#Í�ÑâjÍ<ÏòÕ*Ñ5â ÍYÍ Î Ö Í Î Ï�Ñ�ÖTÍ�¯ Î Ð<Ô?´5ÍÃä ± ÍuÐ�éüä3ÑyÏ.¯Cä3â Ñ�ÖTÍøåOÐ Î!ßH± Õ#â Ì Ö Ñ0Ð Î�Ì�Î ä�Ï$Ö Ì ÖjÍ,¸���ÐTÔAÍ�ÖTÍvâZá%$ ïúÐ�â ÖLôPº'&ä3ÍÃÏ å±âjÑ ² ÍIÏ�æ#Ð<ÔùÖjæ#Í Î ÍIå±ÍIÏjÏ Ì â0ÑYÏjåµæ#ÍÃä3Õ|´5Ñ Î|± Ñ Î é|Ð�â�æ Ì ÖjÑ5Ð Î å Ì�Î�² Í�Í Î Ö â Ì å±ÖjÍIä�é|â Ð\æÓæ:Ð�ä3ÍZâ Î ¼ Ô ¼�%ä3Ñ�Ï3¯ ä3â Ñ�ÖTÍIÏüé|Ъâ�Õ4Ï$ÍVÑ Î æ#ÐïÏ�Ö Ó ²4Ì Ï�ÍIäùÏjåµæ*ÍIä3Õ|´0Ívâ<ÏÞ¸Y% Î Ð�âöä3Ívâ�é|Ð�â Ì æ#ÐïÏ�Ö Ó�²4Ì Ï�ÍIä?é|Õ|´�´ Ó ¯ Î Ð<Ô?´0ÍIä ± ÍÏjåµæ#ÍÃä3Õ|´5ÍZâ�Ö ÐCÍ Ü ÍIå±Ö Ñ�ÖTÍ�´MÑ×Õ#Ö Ñ�´5ÑMáZÍ ³�Ô�³ ¼CåOÐPæ�æ ÌIÎ ä Ó ÏòÕ*ÍvÕ#ÍIäCä3ÑyÏ.¯#ÏOáQÑ5Ö�æ�Õ4Ï�Ö Ì ´�Ï�Ð ² Í ÌT² ´0Í[ÖjÐÐ#âjÍIä3Ñ�å±ÖYâ Í<ÏTÕ#ÍIÏ$ÖVå±Ð\æ�Ð|´5ÍZÖ Ñ5Ð Î ÖjÑMæ:ÍÃÏ Ì�Î ä Ð4ÍvâjÑMÐ#æ#ÍZâ Ì ´ ² Õ4ÏøÕ#ÖjÑM´0ÑMá Ì Ö Ñ5Ð Î ¸�% Î ÍIÏjÏ�Í Î å±ÍTá Ì æ*ÐTÏ�Ö Ó²4Ì Ï�ÍIä�¼òç�Õ ³ Ï å<æ#ÍIä�Õ|´5Ívâ�Õ4Ï$Ñ Î|± ³�Ô�³ ¼Cå±Ð\æ�æ ÌIÎ ä Ó ÏòÕ#ÍZÕ#ÍIä:ä3Ñ�Ï3¯*Ï Î ÍvÍÃä#ÏÖ Ð ² Í ÌT² ´5ÍVÖ Ðíë<Ï�Ñ�æ ÓÕ|´ Ì ÖjÍ<ì[ä�ÑyÏ3¯ ÌIÎ ä ² Õ Ï Ì å±ÖjÑMÖ�Ñ5Ö.ÑVé|Ð�â�Ö æ#ÍuÑMæ�æ:ÍÃä3Ñ Ì Ö Í�é|Õ#ÖjÕ#â Í,¸ ½ Ï å Ì ´5ÍÃä Ó ä�ÐTÔ Î ä3ÑyÏ.¯CÏ�Õ ² Ï.Ñ#Ï$Ö Í�æÏ$ÑMæ�Õ|´ Ì Ö Ð�âóå±ÐªÕ|´yä�Ð#â Ð<Ö�Ñyä3Í�Ö æ*ÑyÏ�é|Õ Î å±Ö Ñ0Ð Î4Ì ´5Ñ5Ö.Ñ,¸"Õ�æ#Í Ì ä*ä3Ñ5ÖjÑ5Ð Î Ì ´Aå±ÐPæ�Ð#Õ#Ö Ì Ö Ñ0Ð ÎúÌ�Î ä�æ:Í�æ:Ъâ0ÑâjÍIÏ�ЪÕ#â<å±ÍÃÏ�å±Ð Î Ï$Õ|æ:ÍIä ² Ñ:Öjæ#ÍuÏ�Ñ�æ[Õ|´ Ì ÖjÑ5Ð Î Í Ü Ð�âjÖ�Ï$æ#Ð�Õb´yä Ì ´yÏ$Ð ² Íuå±Ð Î Ï�Ñyä�Ívâ ÍIäE¸

" î Î Ð�ÍZâ ÑMæ×Í Î ÖöÏ Ñ Î Ö æ#Ñ�Ï]ä3ÑyÏjÏ�ÍvâjÖ Ì ÖjÑ5Ð Î Ï$æ#Ð<ÔqÖ æ Ì Ö�Ð Î#Ó ² Ð Ì âöä ä Ì Ö Ì å Ì å<æ#Í�å±Ð Î!ßH± Õ#â Ì Ö Ñ5Ð Î Ï�å Ì�Î Ï$Ñ ±�ÓÎ Ñ ß å ÌIÎ Ö�´MÑVÑMæ�Ð Ì å±ÖAÏjåµæ#ÍÃä3Õ|´5Ñ Î|± Ð4Ívâ$é|Ð�â�æ Ì�Î åOÍ,¸�% Î Ð Ì â ÖjÑyå±Õ|´ Ì âZá3Ö æ*ÍYåµæ*Ð�ÑyåOÍ�Ð�é�Ô�æ#Í Î ÖjÐVÑ Î Ñ0Ö Ñ Ì Ö ÍÐ#âjͱé|ÍvÖöåµæ Ì åOÖ ÑMÖ�Ñ5Ö.Ñ ­ Í,¸ ± ¸5á Ì é|Ö Ívâ�â Í Ì ä?æ#Ñ5ÖöÏ�ЪââjÍ Ì ä�æ×ÑyÏ Ï$ÍIÏ�Ð�â ² ÐªÖ æ ®�Ì�Î ä?Öjæ#ÍVå<æ#Ð�Ñ�å±ÍYÐ�éüå Ì åµæ#ÍÏ$Í ± æ:Í Î ÖüÏ�ÑMáZÍ ­ Ð�â�Ö æ#Í Î Õ|æ ² ÍZâ�Ð�é�Ï�Í ± æ:Í Î Ö<Ï ® Ï�Ñ ±�Î Ñ ß å Ì�Î Ö0´�Ñ:ÑMæ�Ð Ì å±ÖAÖ æ#Í�Ð4Ívâ$é|Ð�â0æ Ì�Î å±ÍóÐ�é]Öjæ#ÍÏjåµæ#ÍÃä3Õ|´5ÍZâ�ÑMæ�Ðb´5Í�æ�Í Î Ö Ì Ö Ñ0Ð Î Ï�Ï�ÖjÕ4ä3Ñ5ÍÃäp¸ ½ Ï�Ð Î#Ó�² Ð Ì â<äûä Ì Ö Ì å Ì å<æ#ÍIÏ ² ÍIåOÐPæ:Í�æ:Ъâ Í�å±Ð\æ�Ð|´0Í Î áÐ4Ívâ$é|Ð�â0æ Ì�Î å±Í�ä�Í�æ Ì�Î ä#Ïuæ Ì Ñ Î ÍIå±ÍIÏjÏ�Ñ5Ö Ì ÖjÍ ÌIÎ Í Î Ð|´5Ñ�å±Ñ5Ö�Ñ Î Ö Ívâ$é Ì å±Í ² ÍvÖ.ÔAÍvÍ Î Í Î Ö Ívâ Î4Ì ´]âjÍ<ÏòÕ*ÍIÏ�ÖÏjåµæ#ÍÃä3Õ|´5ÍZâ<Ï Ì�Î ä:Ð Î#Ó�² Ð Ì â<äCå Ì å<æ#Í�æ Ì�Î ÌT± Í#æ:Í Î Ö Ì ´ ± Ð�âjÑ5Öjæ|æ&Ïl¸�Õ�æ Ì ÖAÑyÏOá#Ï å<æ#ÍIä�Õ|´5ÍvâöÏ Ì�Î ä&å Ì åµæ#Íæ ÌIÎ4ÌT± Ívâ<ÏBæ Ì Ñ Î ÍvÍIäøÖjÐuå±ÐTÐPÐ4Ívâ Ì Ö Í�Ñ Î Ðªâ<ä3ÍZâ�Ö Ð Ì åµæ*Ñ5Í�ÖTÍAæ#Ñ ± æ�Ð�ÍZâ�é|Ð�â�æ Ì�Î å±Í,¸BÕ�æ#Í�ä3ÍIÏ$Ñ ±ªÎ�Ì�Î äÍ Ü ÍIåOÖ ÑMÖTÍ�Õ4Ï$ÍøÐ�é Ì Ï å<æ#ÍIä3Õ|´0Ívâ��Ãå Ì å<æ#Í�Ñ Î Ö Ívâ$é Ì å±ÍóÑyÏ Ì�Î Ð#â Ð\æ:ÑyÏ$Ñ Î|± Ì âjÍ Ì é|Ъâ�é|Õ#Ö Õ*â ÍYâ ÍIÏ$Í Ì âöåµæ�¸

" Õ�æ#Í�Ä}° Ïjåµæ*ÍIä3Õ|´0Ñ Î|± Ì ´ ± Ð�âjÑ5Ö æbæ&Ï]Ï�Ö Õ ä3Ñ5ÍIä�Ñ Î Öjæ#ÑyÏ�ä3Ñ�Ï Ï$Ívâ Ö Ì Ö Ñ0Ð Î�± ÑMÖTÍuÐ*â Ñ5Ъâ Ñ0Ö3ÑVÖjÐVÖ Ñ�æ:Í Ó å±â Ñ0Ö Ñ0å Ì ´ÌIÎ äcÖjÑMæ:Í Ó ´0ÑMæ�Ñ5Ö ÍZä�â Í<ÏTÕ#ÍIÏ$Ö<ÏOá�Ö æ#ÍZâ Í ² Ñ Ì åµæ#Ñ0Í�Ö�Ñ Î|±�² ÍvÖ ÖjÍvâ]ÐTÖTÍZâ Ì ´�´#Ï.Ñ#Ï$Ö Í�æüÐ4Ívâ�é|Ъâ0æ ÌIÎ å±Í,¸BÕ�æ#ÍIÏ$ÍÌ ´ ± Ъâ Ñ0Ö æ|æ&Ïuå±Ð�Õb´yä ² Í æ:Ð�ä3Ñ ß ÍIä�Ö Ð�Ð Î ´MÑ ± ÑMÖTÍ"Ð#â Ñ0Ð�â Ñ0Ö.Ñ ÖjÐ�Ö ÑMæ×Í Ó ´0ÑMæ�Ñ�Ö ÍIä?âjÍ<ÏòÕ*ÍIÏ�ÖöÏEÖ æ Ì Ö Ì âjÍÑ Î ä ÌIÎ|± Ívâ�Ð�éAÍ Î å±ÍvÍÃä3Ñ Î|± Ö æ#ÍZÑ5â�Ö ÑMæ×Íu´5Ñ�æ:Ñ5ÖöÏl¸8Õ�æ#Ñ�Ïå±ÐªÕ|´yä&ÑMæ�Ð*â Ð<ÖTÍ�â ÍÃÏ3Ð4Ð Î Ï$ÍøÖjÑMæ:ÍIÏ�é|ЪâÖjÑMæ:Í Óå±âjÑ5ÖjÑyå Ì ´�âjÍ<ÏTÕ#ÍIÏ�Ööϱá Ì ´ ² ÍvÑ5Ö Ì Ö�Ö æ#Í]âjÑyÏ3¯óÐ�é*æ Ì Ö3Ñ Î|± æ:Ð�âjÍQÖjÑMæ:Í Ó ´0ÑMæ�Ñ5Ö ÍÃä�â Í<ÏTÕ#ÍIÏ$Ö<Ï�Í Î å±ÍZÍIäÖ æ*ÍvÑ5âE´5ÑMæ ÓÑ0Ö<Ïl¸�% ÎøÌ ä#ä3Ñ0Ö Ñ5Ð Î á�Öjæ#ÑyÏså±Ð�Õb´yäEâjÍIä3Õ4åOÍ�Öjæ#Í�Ï$Ö Ì â0Ö Ì ÖjÑ5Ð Î ÐIé Ö ÑMæ×Í Ó¤Î Ð Î å±âjÑ5ÖjÑyå Ì ´�âjÍ<ÏTÕ#ÍIÏ�ÖöÏ ­ Í,¸ ± ¸5á�Ô�âjÑ5Ö ÍâjÍ<ÏòÕ*ÍIÏ�ÖöÏ ± Í Î ÍZâ Ì ÖjÍIä ² Ñ Ì å Ì å<æ#Í(�4Õ4Ï$æ�ä Ì Í�æ:Ð ÎE® ¸Rò?Ъâ ÍuÏ�Ð\Ð#æ#Ñ�Ï�Ö Ñ�å Ì ÖjÍIä Ì ´ ± Ð�âjÑ5Öjæ|æ&Ï�å±ÐªÕ|´yä ² Íä3Í#ÖTÍ�´5Ð\Ð�ÍÃä ÖjÐVÕ#Ö Ñ�´5Ñ�ávÍ Ì ä*ä3Ñ5ÖjÑ5Ð Î Ì ´�Ï3Ñ*Ï�Ö Í#æ Ó ´0Í�ÖTÍ�´#Ñ Î é|Ð�â�æ Ì ÖjÑ5Ð Î Ð�â�æ Ì ¯TÍ ² ÍZÖ Ö ÍZâ�Õ4Ï�ÍuÐ�é]âjÍ<ÏòÕ*ÍIÏ�ÖÐ#âjÑ5Ъâ Ñ5ÖjÑ5ÍIÏ)��Ö æ*Í�ä3ÍÃÏ�Ñ ±ªÎ Ï3Ð Ì å±Í�é|Ð�âAÏ å<æ#ÍIä�Õ|´5Ñ Î|±uÌ ´ ± Ð�âjÑ5Ö æbæ&ÏQÖ æ Ì Ö�Õ Ï�ÍóÏ3Ñ*Ï�Ö Í#æ Ó ´0Í�ÖTÍ�´TÑ Î é|Ð�â�æ Ì ÖjÑ5Ð ÎâjÍ�æ Ì Ñ Î Ï�âjÍ�´ Ì Ö Ñ�ÖTÍ�´MÑuÕ Î Í Î Ð|´5Ъâ ÍIäE¸

" Õ�æ#Í�æ*ÐTÏ�Ö ÌIÎ ä Ö æ#Íúä�ÑyÏ3¯ æ Ì ÖTÍ ² ÍvÍ Î Í Î#Ì æ:Ñ Î ÍÃä Ì Ï�Ð�ÐªÖ Í Î Ö Ñ Ì ´�Ð Ì âjÖ Ñ�å±ÑMÐ ÌIÎ ÖöÏ[Ñ Î Ïjåµæ*ÍIä3Õ|´0Ñ Î|±Ì å±Ö Ñ�Ö3Ñ0Ö Ñ5ÍÃÏl¸�% Î Ö Ívâ�æ:ÍIä3Ñ Ì Ö Í�%��P× å±Ð Î Öjâ Ð\´M´5ÍZâ<Ï Ì�Î äVä3ÑyÏ.¯ Ì â â Ì Ñuå±Ð Î Öjâ Ð\´M´5ÍZâ<Ï�å±ÐªÕ|´yä Ì ´yÏ$ÐuÐ Ì â Ö Ñ�å±ÑMÐ Ì Ö ÍÑ Î ä�ÑyÏ3¯&âjÍ<ÏòÕ*ÍIÏ�Ö�Ïjåµæ#ÍÃä3Õ|´5Ñ Î|± ¸ Ô Ð Î Öjâ Ð\´M´5ÍZâ Ó ´5Í�ÖTÍ�´ Ïjåµæ#ÍÃä3Õ|´5ÍZâ<Ï�å±ÐªÕ|´yä:Ñ Î å±Ð�â�Ð�Ъâ Ì Ö Í�¯ Î Ð<Ô?´5ÍIä ± ÍYÐ�é

Page 210: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô,¹

âjÍIÏ�ЪÕ#â<å±Í ­ Í,¸ ± ¸5á�ä3ÑyÏ.¯ ÌIÎ ä ² Õ4Ï ® Õ#Ö Ñ�´5ÑMá Ì Ö Ñ0Ð ÎûÌIÎ äùÖ æ#Í Ï�Ö Ì Ö Í&Ð�é ÌIÎ Ñ Ì ä#ä3Ñ0Ö Ñ0Ð Î4Ì ´�ä Ì Ö Ì å Ì å<æ#ÍIÏÌ ´5Ð Îb± Öjæ#Íu%��\×ÓÐ Ì Ö æ�¸

" ó Í<ÏTÕ#ÍIÏ�Ö×Ï å<æ#ÍIä�Õ|´5Ñ Î|± é|Ð�â ä3ÑyÏ.¯ Ì âjâ Ì Ñ*Ï Ñ Î ÖTÐ\´MÖTÍIÏ Î Í�ÔoÑyÏ Ï$Õ#ÍIÏOá�Ï�Õ åµæ Ì Ï[â ÍIä�Õ4å±Ñ Îb± å±ÐPæ ² Ñ Î ÍIäÏ$Ívâ0Ö�Ñyå±Í]ÖjÑMæ:ÍIÏ�é|ЪâRæ�Õ|´5ÖjÑ Ó ä3ÑyÏ.¯ Ì åvå±ÍIÏjÏ�ÍIÏOá ß4Î ä3Ñ Î|±YÌIÎ�Ì Ð|Ð#âjÐPÐ#âjÑ Ì Ö Í�Ð#â Ñ0Ð�â Ñ0Ö.Ñu´5Í�ÖTÍ#´�é|Ð�â�âjÍIä3Õ Î ä Ì�Î Öä Ì Ö Ì Õ|Рä Ì Ö ÍIÏOá Ì�Î ä�Ï$Í�´5ÍÃå±Ö Ñ Î|±�² ÍvÖ.ÔAÍvÍ Î æ�Õ|´0Ö ÑMÐb´5Íóä Ì Ö Ì Ï$Ð�Õ#âöå±ÍIÏÞ¸ ½ Î Õ|æ ² Ívâ�ÐIéüä Ì Ö Ì ´ Ì ÑTÐ�Õ#ÖÏjåµæ#Í#æ:ÍIÏ ÌIÎ äqâ ÍIä3Õ Î ä Ì�Î ålÑmæ:ÍIå<æ Ì�Î Ñ�Ï3æ&ÏYæ Ì ÖTÍ ² ÍvÍ Î Ð#â Ð\Ð4ÐTÏ�ÍÃä ÌIÎ ä ÑMæ�Ðb´5Í�æ�Í Î Ö ÍIäp¸�î Ì å<æÐ#âjÍIÏ�Í Î ÖöÏ�Õ Î Ñ�ÏTÕ#Í�Ð\Ð|Ð4Ð�âjÖ Õ Î Ñ0Ö Ñ0ÍIÏüé|Ъâ Ì<±P± â ÍIÏjÏ�ÑMÖTÍuÏjåµæ#ÍÃä3Õ|´5Ñ Î|± Ð\Ð#Ö Ñ�æ:ÑMá Ì Ö Ñ0Ð Î ÏÞ¸

Page 211: Aggressive Centralized and Distributed Scheduling ofDisk Requests

_�ÿ ÿ*�,+ � P.- _

þ ÿ ý ;V;0/:8 � H'%� � U�HZa�B ÿ XuU�XVW BN�B�U1

Õ�æ#Íøé|Ð�2325Ð<Ô�Ñ Î54 Ð Ì â Ì æ:ÍvÖ ÍZâ<Ï?Ô�ÍvâjÍøÕ4Ï$ÍIä?Ö Ð&åOÐ Î!ß�4 Õ#â ÍVÖjæ#Í�Ï�Ñ�æ[Õ52 Ì ÖjÐ�â�ÖjÐ�æ:Ð�ä3Í 2�Öjæ#Í���ç Ô Ä\ÄTÍ76ä3Ñ�Ï98�ä�â ÑMÖTÍ�:uÕ�æ#Í�Ñ ÔAÍvâ ÍVÐ�;#Ö Ì Ñ Î ÍIä<;4ÐªÖ æ�é|â ÐPæ¾æ ÌIÎ Õ�é Ì å±ÖjÕ#â ÍvâóÏ3Ð4ÍIåOÑ ß å Ì Ö Ñ0Ð Î Ï ÌIÎ ä é|â Ð\æ�ä3Ñ0â ÍIåOÖÐ�; ÓÏ�ÍZâ0Ö Ì ÖjÑ5Ð Î Ð�é>= Ô =�%�;#Õ4Ï Ì å±ÖjÑMÖ�Ñ5Ö.Ñ?:

Õ Ì ;�25Í>@A: ê å±Ð Î Ö Ì Ñ Î Ï�Ï�Í�ÖTÍZâ Ì 2 ßHÎ ÍIä Ì�Î ä�Ö Ì âjÑ Ì ;525ÍRÐ Ì â Ì æ:ÍvÖ ÍZâ<Ï�Õ Ï�ÍIä�Ñ Î å±Ð Î!ßB4 Õ#âjÑ Î�4 Ö æ#ÍA��ç Ô Ä\ÄTÍ76ä3Ñ�Ï98 æ:Ð�ä3Í 2C:Õ�æ*Íøæ#ÐïÏ�ÖYÏ.Ñ#Ï$Ö Í�æoÕ4Ï$ÍIä?ä3Õ*â Ñ Î54 Öjæ#ÍøÍ Î Ö â Ì å±ÖjÑ5Ð Î Ô Ì Ï ÌIÎ à Ô�ó Ì�D�D�E�æ�Õ�25ÖjÑMÐ#âjÐ�å±ÍIÏjÏ�Ð�â#:=TÐ\æ:ÍVÐ�é�Öjæ#Í�Ö Ì 20Õ#ÍIÏ 4 Ñ�ÖTÍ Î åOÐ Î Ö Ì Ñ Î å±Ð\æF;#Ñ Î4Ì ÖjÑ5Ð Î ÏÐ�éóä�ÑyÏ98 ÌIÎ äùæ#ÐTÏ$ÖVä3Í#2 Ì Ñ#Ï):HG#Ð�âYÍ Î*Ì æ�Ð�20ÍTá�Öjæ#Íæ#ÐïÏ�ÖóÏ3Ñ*Ï�Ö Í#æJI ΠЪÖ�Ö æ#Íu��ç Ô>K�K Í76�LM25ÑMæ×Ñ5Ö<Ï�Öjæ#Íuä Ì Ö Ì Öjâ Ì�Î Ï¿é|Ívâ�â Ì Ö ÍIÏ 4 ÑMÖTÍ Î Ñ Î Õ Ì ;�25ÍN@A: ê :

Õ Ì ;�25ÍO@P: K Ï3Ð4ÍIå±Ñ ß ÍIÏVÖ æ#ÍQ2 Ì ÑTÐ�Õ#Ö�Ð�éuÖjæ#Í���ç Ô>K�K ÍR6T��Ï:ÍvÑ 4 æ�Ö�áZÐ Î ÍIÏ):Óò?ÐïÏ�Ö:ÐIéYÖ æ#Ñ�Ï[Ñ Î é|Ð�â0æ Ì�ÓÖ Ñ0Ð Î ÑyÏ Ì Ö Ì Ñ32 Ì ;�25ÍVÑ Î Öjæ#Í�ä3ÑyÏS8úä3â Ñ�ÖTÍVÏ.Ð�ÍÃå±Ñ ß å Ì Ö Ñ0Ð Î Ï):T@U2V2]ÏS8TÍ�ÔõÖ Ì 25Õ*ÍIÏ Ì â Í 4 Ñ�ÖTÍ Î Ñ Î Ï$ÍIå±ÖjÐ�â<Ï):"Õ�æ#Í=TÍ Î äW� ó ÍIå±ÍvÑ�ÖTÍ0XÑ Ì�4�Î ÐTÏ�ÖjÑyåF= Ô =ò%å±Ð\æ�æ ÌIÎ ä#ÏÔ�ÍZâ ÍYÕ4Ï�ÍÃä?Ö Ð:Ð�;#Ö Ì Ñ Î é|Õ�232Y20Ð 4 Ñ�å Ì 2 Ó ÖjÐ Ó Ð#æ�Ñ#Ï$Ñyå Ì 2�æ Ì Ð ÓÐ#Ñ Î�4 Ï�é|Ð�âVÍvÑ 4 æ�Öøä�Ñ Ü Ívâ Í Î Öuä3Ñ�Ï98*Ï�:�Õ�æ#Ñ�Ï�Ð#âjÐ<Ö3Ñ�ä3ÍIäùä Ì Ö Ì Ð Î Ö æ#Í ß â<Ï$ÖA25Ð 4 Ñ�å Ì 2üÏ�ÍIå±ÖjÐ�âuÑ Î Í Ì åµæ�ávÐ Î ÍÌ�Î ä Ì 2325Ð<Ô�ÍIä�ÖTÍvâjÑ ß å Ì Ö Ñ0Ð Î Ð�é�Ð�Öjæ#Ívâ ä Ì Ö Ì 2 Ì ÑTЪÕ#Ö�Ð Ì â Ì æ:ÍvÖjÍvâ<Ï): Õ�æ#Í ß âöÏ�Ö ê 6:Öjâ Ì åZ8*Ï Ì â Í�â ÍIÏ$Ívâ0ÖTÍIäé|Ð�âYÑ Î ÖjÍvâ Î4Ì 2�Õ4Ï$Í?:T@U2V2�Ï3Ð Ì â Í�Ö â Ì å�8#Ï Ì âjÍ�Ð52 Ì åOÍIä Ì ÖYÖ æ*Í[Í Î ä~ÐIé�Í Ì åµæ�ávÐ Î Í?:"Õ�æ#Í×��ç Ô>K�K ÍR6&Õ4Ï�ÍÃÏÖ â Ì å�8 Ó ; Ì Ï�ÍIä�Ï.Ð Ì âjÑ Î�4 é|ЪâU;4ÐªÖ æ�Ï925Ñ�Ð|Ð4ÍIä ÌIÎ ä�ä!Ñ Î4Ì æ×Ñyå Ì 2V2MÑ�â Í Ì 2V20Ð�å Ì ÖjÍIä?ä�ͱé|ÍIå±ÖöÏ�:�Õ�æ#ÍVä�ͱé Ì Õ�20Ö�ä�ÑyÏ98å±Ð Î!ß�4 Õ*â Ì ÖjÑ5Ð Î Ñ Î Ö æ#Í�Í Î Ð4Ívâ Ñ�æ:Í Î Ö<Ï�æ Ì Ï8ÌPÛYÏ920ÑMÐ|Ð4ÍIäøÖjâ Ì å�8*Ï1I�æ Ì Ö<å<æ#Ñ Î54 Ö æ#Í[2 Ì â 4 ÍIÏ�ÖAä3ÍOé|ÍIå±Ö%25ÑyÏ$Ö é|ÐªÕ Î äÑ Î Öjæ#ÍuÏ�ÍvÖ�ÐIé]ÍvÑ 4 æ3ÖAÍ Î Ð�ÍZâ ÑMæ×Í Î Ö Ì 24�óç Ô>K�K Í76×ä3Ñ�Ï98×ä3â Ñ�ÖTÍIÏZL�:

Õ Ì ;�25Í\@A:ÅÌ�Ð*â ÍIÏ$Í Î ÖöÏ�Ö æ#Í�æ#Í Ì ä:Ï3Ô�Ñ0Ö<å<æ�áTÏ�ÍZÍ 8�á ÌIÎ ä:Ï�ÍZÖ Ö�20Ñ Î�4 ä3Í#2 Ì Ñ#ÏsÐ�;4Ï$Ívâ0ÖTÍIäøé|Ð�âAÖ æ#Íó��ç Ô>K�K ÍR6?:@{é|Õ�2V2�Ï�ÍvÍ#8&å±Õ#â�ÖTÍ�ÑyÏ 4 ÑMÖTÍ Î Ñ Î�ß�4 Õ#â ÍP@A: ê :8Õ�æ#ÍÃÏ�Í�Ö Ì 25Õ#ÍIÏÔAÍvâ ÍYÐ�;#Ö Ì Ñ Î ÍIä�Ö�Ñ Ì Í Î Ö Í Î Ï�Ñ�ÖTÍ�â Í�Ð4ÍvÖjÑ5ÖjÑ5Ð ÎÐ�é~Ð#â ÍÃä3ÍvÖ ÍZâ0æ:Ñ Î ÍIä&Ï�ÍvÍ#8�ä3Ñ�Ï�Ö ÌIÎ å±ÍIÏ Ì�Î ä Ì Ð|Ð#âjÐPÐ#âjÑ Ì ÖjÍ�æ×Ð Î Ñ0Ö Ð�âjÑ Î�4 Ð�é(= Ô =�% Ì å±Ö Ñ�Ö3Ñ0Ö.Ñ Õ Ï�Ñ Î54?Ì 20Ð 4 Ñ�åÌ�Î Ì 2MÑ�ávÍvâ#:]=ïÍvÍ 8ûä3Ñ�Ï�Ö Ì�Î å±ÍÃÏ 4 â Í Ì Ö Ívâ�Ö æ ÌIÎ ÖjÍ Î ålÑ720Ñ Î ä�Ívâ<ÏVå ÌIÎ ;4Í Ì Ð|Ð*â Ð Î Ñ�æ Ì ÖjÍIä^;!Ñ Ì Ö.Ô�Ð Ó Ð*Ñ5ÍIå±Íå±Õ#â�ÖTÍ?:_@U20Ö æ#ÐªÕ 4 æúÖ æ*Í[Í Î*Ì åOÖ�Ð<ÖTÍvâ�2 Ì Ð�;4ÍvÖ.Ô�ÍvÍ Î å±ÐPæ�æ Ì�Î ä&ÐTÖTÍZâ æ#Í Ì ä Ì�Î äúÏ�ÍZÍ 8?Ñ Î Ñ5ÖjÑ Ì ÖjÑ5Ð Î å Ì�Î#Î Ð�Ö;4ÍÍ Î Öjâ Ì åOÖ ÍIäVÍ�æ�Ð#Ñ0â Ñ�å Ì 232yÑïáIÏ�Í�Ð Ì â Ì Ö ÍYå±Ð\æ�æ ÌIÎ äEÐ<ÖTÍvâjæ#Í Ì ä ÌIÎ ä:Ï$ÍvÍ 8�Ö Ì 20Õ#ÍIÏ�æ Ì ÖTÍ[;4ÍvÍ Î ä3ÍZÖ Ívâ�æ:Ñ Î ÍÃäÔ�æ#Ñ�åµæ&Ö Ð 4 ÍvÖjæ#Ívâ Ì åvå±Ð�Õ Î Ö�é|ЪâÖjæ#ÍYÐ�;4Ï$Ívâ0ÖTÍIäT;�ÍZæ Ì Ö3Ñ0Ð�â :

Õ Ì ;�25ÍT@P:öÍ`20ÑyÏ�ÖöÏ*Ö Ì âjÑ5Ð�Õ Ï�æ×Í Ì Ï$Õ#â ÍIäCå±Ð Î Ö âjÐ�2 Ì�Î äúå±Ð\æ�æ[Õ Î Ñyå Ì Ö Ñ0Ð Î Ð<ÖTÍvâjæ#Í Ì ä*Ï�:u% Î æ×ÐTÏ�Öóå Ì Ï�ÍIÏOáÖ æ*ÍIÏ�Í�Ö Ì 20Õ#ÍIÏ Ì â ÍuÏ�Í Î Ï�Ñ0Ö ÑMÖTÍ�Ö Ð�Ö æ*ÍYåµæ Ì â Ì å±Ö ÍZâ ÑyÏ$Ö Ñ�åvÏ�ÐIéa;4Ð�Öjæ?Öjæ#ÍYå±Õ#âjâ Í Î Ö�âjÍ<ÏTÕ#ÍIÏ�Ö ÌIÎ ä:Ö æ#ÍYÑ�æ�æ[ÍÃä3Ñ ÓÌ ÖjÍ 2MÑ�Ð#â Í#Ö3Ñ0Ð�Õ4Ï�â Í5ÏòÕ#ÍÃÏ�Ö :N@U2yÏ$Ð#á�Öjæ#Í:å Ì å<æ#Í�å±Ð Î Ö Í Î ÖöÏ Ì5Ü ÍIå±ÖYÖjæ#Í[Ð�;4Ï�ÍZâ0ÖTÍIä�ä3Í#2 Ì Ñ#Ï):V% Î Ö æ#Í×å Ì Ï�Í�Ð�éå±Ð Î Ï�ÍIåOÕ#Ö Ñ�ÖTÍ Î Ð Î#Ó Ï�Í<ÏTÕ#Í Î Ö Ñ Ì 2BÔ�â Ñ0Ö ÍøâjÍ<ÏTÕ#ÍIÏ�Ööϱá#Öjæ#Í�Ï�ÍIåOÐ Î ä Ô�â Ñ5ÖjÍøÑ Î å±Õ#âöÏ ÌIÎúÌ ä#ä3Ñ0Ö Ñ0Ð Î4Ì 2]ä3ÑyÏjå±Ð Î*Î ÍIå±ÖI¤Ñ�æ�æ:ÍZä3Ñ Ì Ö Í 2�Ñ Ì é|ÖjÍvâ�â ÍÃå±ÍvÑMÖ�Ñ Î54 Ö æ#Í�å±Ð\æ�æ ÌIÎ äWL Ì�Î ä~æ Ì Ï�ä3Ñ Ü ÍZâ Í Î ÖÐ<ÖTÍvâjæ#Í Ì ä�ä3Í 2 Ì Ñ*Ï�Öjæ Ì�ÎúÌ Ô�âjÑ5Ö Íé|Ð�2325Ð<Ô�Ñ Î54:Ì â Í Ì ä âjÍ<ÏòÕ*ÍIÏ�Ö�Ъâ Ì Ï$Í<ÏTÕ#Í Î Ö Ñ Ì 2pÔ�âjÑ5Ö Í�:?ò?ÐTÏ$ÖÐIé]Ö æ#Í ë�Ð#â Í�Ð Ì â Ì Ö Ñ0Ð Î ì&ä3Í 2 Ì Ñ#Ï Ì â ÍVå Ì Õ4Ï$ÍIä;�Ñ:Ö æ#ÍYæ#ÐïÏ�ÖóÏ3Ñ*Ï�ÖjÍ�æ â Ì Öjæ#Ívâ�Ö æ ÌIÎ Ö æ*Íøä�ÑyÏ98×ä3âjÑMÖTÍ?:

(�Ï�Ñ Î�4 Ö æ*Í Ì ;4ÐTÖTÍ�Ð Ì â Ì æ:ÍvÖ ÍZâÖ Ì 20Õ#ÍIÏ�é|Ð�â�Ö æ*Íø�óç Ô>K�K Í76ïá�Ö æ#Í�æ:Ð�ä�Í 2�Ï$Ö ÑV232�ä3Í#Ö3Ñ Ì Ö ÍÃÏb;�Ñ Ì Ï.æ Ì 232Ì æ×Ð�Õ Î Ö�é|âjÐPæeÖjæ#ÍYÐ�;4Ï$Ívâ0ÖTÍIä`;4Ívæ Ì Ö�Ñ5Ъâ : õ Ñ Ì ä#ä3Ñ Î54�Ì ä#ä3Ñ0Ö Ñ0Ð Î4Ì 2�Ô�âjÑ5Ö ÍóÐTÖTÍZâ æ#Í Ì ä&ä3Í 2 Ì Ñ*ϱá�Ö æ#Ñ�Ï�ä3Í�Ö�Ñ Ó

ê ô\Û

Page 212: Aggressive Centralized and Distributed Scheduling ofDisk Requests

ê ô\ô

Ô Ð Î Ï$Ö Ì�Î Ö - Ì 20Õ#Íó ÐªÖ Ì Ö Ñ5Ð Î4Ì 2�=,Ð4ÍvÍIä DTÍ�E�E ó ç8ò

ÔAÌ åµæ#Í_=TÑ�ávÍ K D�c�Ø õó Í Ì äHX Ì Ö Ì Õ�â ÌIÎ Ï¿é|ÍZâ Ì7:dE ê ò õ �IÏïúâ Ñ0Ö ÍPX Ì Ö Ì Õ�â ÌIÎ Ï¿é|ÍZâ K :e6�Í�ò õ �IÏ

ó Í Ì ä Õ�â Ì�Î Ï¿é|Ívâ\XÑyÏjå±Ð Î*Î ÍIå±Ö àÐ

- Ì âjÑ Ì ;525Í - Ì 25Õ#ÍÔAÌ å<æ#Í_=TÍ 4 æ×Í Î ÖöÏ K

ó Í Ì ä�ï Ì Ö Ívâ�æ Ì âf8 6'D�Òï âjÑ5Ö Íhï Ì Ö Ívâ�æ Ì âf8 6'D�Ò

ç�â ÍOé|ÍvÖ<å<æ ò?Ñ Î ÑMæ�Õ|æ E�Ø õç�â ÍOé|ÍvÖ<å<æ ò ÌTÎ ÑMæ�Õ|æ cTÍ�Ø õ

6�þ#7�ÿ|Ü�g?Ý|ñ4ß�ç Ì â Ì æ:ÍZÖ ÍvâöÏ�é|Ð�âhò?Ð�ä3Í 20Ñ Î�4 Öjæ#Íu��ç Ô>K�K ÍR6VÐ Î Ö æ*Í�à Ô�ó Ì�D�D�E:Ï.Ñ#Ï$Ö Í�æ

h4Ð Î Í GQÑ5âöÏ�Ö ð�Ì Ï�Ö =TÍIå±ÖjÐ�â<Ï ê Ï$Ö ð Ð 4 Ñ�å Ì 2 Õ�â Ì åZ8 Ô Ñ72 ó Ï�â�Ö#ä =,Ð Ì â ÍÔ ÑR2 Ô ÑR2 �5Õ â Ì å�8 =TÍÃå±Ö Ъâ =?8TÍ�Ô =�8TÍ�Ô Õ�â Ì åZ8*Ï Õ�â Ì åZ8*Ï

ê E D�DPÛ ô�c E ê Í Ì K ê 6 Ì K DK D�DPô 6'c�E ô K ê Í ê Ì Ì�E E ê Ì�EÌ 6'c ê ô�E ê Û\Û 65Ì ê Ì K ô E c�DÍ ô�E K ê E�D ê Û<Í Û�E ê K K Û E 65ÛD ê E�D K ê�ê ôPÌ Û�E D K ê K K 6 E D Kc êªê ô<Í ê D ê ô 6 K E ê�ê K Í E ê E<Í6 ê D K E ê 65ôPÌ c<Í Ì K ê E K�K E 65ÛÛ ê 6<ô<Í K E�D�E D�c Ì�E ô ê ô E c�D

6þ#7Bÿ¤Ü�gCÝôÞ ßUh4Ð Î Í_=,Ð4ÍIå±Ñ ß å Ì ÖjÑ5Ð Î Ï�é|Ð�â�Ö æ#Íu��ç Ô>K�K ÍR6

Ì ÖjÑ5Ð Î å Ì�Î ;4Í�âjÍIä3Õ4å±ÍÃä[Ï$Ñ 4�Î Ñ ß å ÌIÎ Öf2MÑ?:i@U25Öjæ#Ð�Õ 4 æ&Ö æ#ÍÃÏ�Íóä3Í 2 Ì Ñ*Ï�å ÌIÎ#ΠЪÖ1;4Í Ì Ö Öjâ Ñ3;#Õ#Ö ÍÃä[Ö Ð Ì�Î Ñ:ä3Ð�åOÕ Óæ:Í Î Ö ÍÃä�Ð#æ*Í Î ÐPæ×Í Î4Ì á#Öjæ#Í ß4Î4Ì 2�æ:Ð�ä�Í 2�å�20ÐTÏ$Í 2MÑ�æ Ì Ö<å<æ#ÍIÏ�Öjæ#ÍøÐ�;4Ï�Ívâ�ÖTÍIä Ì å±ÖjÑMÖ�Ñ5Ö.Ñ�Ð�é]Öjæ#Íu��ç Ô>K�K Í76ä3Ñ�Ï98�ä�â ÑMÖTÍ�:�Õ Ì ;�20ÍT@A:jDT25ÑyÏ$Ö<Ï�Ö æ*Í Ì ä#ä3Ñ0Ö Ñ0Ð Î4Ì 2�Ð<ÖTÍvâjæ#Í Ì ä?ä3Í 2 Ì Ñ#Ï Ì ä#ä3ÍIä�Ö Ð&Öjæ#Í�æ:Ð�ä3Í 2C:ø% Î Ö æ#Í_2 Ì Ï$ÖÖ.Ô�ÐVÖ Ì ;�20ÍEÍ Î Öjâ Ñ5ÍÃϱá3Öjæ#Íuä3Í 2 Ì Ñ×ä3Í�Ð4Í Î ä#Ï�Ð Î Ö æ#ÍYâ Í5ÏòÕ#ÍÃÏ�Ö�Ï�Ñ�ávÍ_ISk Ï�ÍIå±ÖjÐ�âöÏZL�:

GQÑ 4 Õ#â ÍÃÏ1@A: K äR@P:jDYå±ÐPæ�Ð Ì âjÍÖjæ#Í�â ÍÃÏ3Ð4Ð Î Ï$ÍYÖ ÑMæ×Í�ä3ÑyÏ$Ö â Ñ3;#Õ#ÖjÑ5Ð Î Ï�é|Ð�â]é|Ð�Õ#â�Ö.Ñ�Ð#Ñyå Ì 2|Ö Ì 20Ñyä Ì Ö Ñ0Ð Î â Õ Î Ïå±Ð\æ�Ð Ì âjÑ Î�4 Ö æ*Í�æ:Ð�ä3Í 2 ÌIÎ ä?Ö æ#Í Ì å±Ö Õ Ì 2]Ï.Ñ#Ï$Ö Í�æ�:�Õ�æ#Í�ÔAÐ�âf8720Ð Ì ä*Ï�å±Ð Î Ï�ÑyÏ$Ö�Ð�é~ô�D}Òoâ ÌIÎ ä3Ð\æMâ Í Ì ä#ÏOáô�D,Òeâ Ì�Î ä3Ð\æðÔ�âjÑ5Ö ÍÃϱáHô�D,ÒoÏ$Í<ÏòÕ*Í Î ÖjÑ Ì 2�â Í Ì ä#Ï Ì�Î ä�ô�D,ÒoÏ$Í<ÏòÕ*Í Î ÖjÑ Ì 2�Ô�â Ñ5ÖjÍIϱá4â ÍÃÏ3Ð4ÍIå±ÖjÑMÖTÍ 2�Ñ?:Õ�æ*ÍVä3Í Óæ:ÍvâjÑ5Ö ßB4 Õ#âjÍIÏ(I�ä3Í ß4Î ÍIäF;�ÑQ$ ó Õ#Í�æ�ôTÍ'& Ì Ï�Ö æ#Í�âjÐTÐ�Ö?æ:Í Ì�Î Ï0ÏTÕ Ì âjÍ�æ#Ð�âjÑMávÐ Î Ö Ì 2�ä3ÑyÏ$Ö Ì�Î å±Í(;4ÍvÖ.Ô�ÍvÍ Î Öjæ#ÍÖ.Ô�Ð ä3ÑyÏ$Ö â Ñ3;#Õ#ÖjÑ5Ð Î å±Õ#â�ÖTÍIÏZL Ì âjÍHE7: Í,Ì}Ò×áaER:jD K Ò×á ê :jD\Û}Ò×á Ì�Î älER:ÊôPô,ÒMÐIé�Öjæ#Í"æ:Í Ì�Î â ÍÃÏ3Ð4Ð Î Ï$Í&Ö ÑMæ×ÍIÏé|Ð�âóÍ Ì å<æ�â Õ Î á�â ÍIÏ.Ð4ÍIå±Ö Ñ�ÖTÍ 2MÑ�:*Õ�æ*Í_2 Ì â 4 ÍIÏ$ÖYä3Í�æ×Ívâ Ñ0Ö ß�4 Õ#âjÍVâ ÍIÏ$Õ�25ÖöÏ�é|â Ð\æMÖjæ#Í�Ô�Ъâ�8R25Ð Ì ä?Ð�é~ô�D,ÒîÏ�Í ÓÏTÕ#Í Î Ö Ñ Ì 2]â Í Ì ä#ϱáRÔ�æ#Ñ�åµæ Ì â Í×Õ4Ï�Õ Ì 2V2�ÑûÏ Ì Ö ÑyÏ ß ÍIäm;�ÑúÖ æ#Í�Ð*â ͱé|ÍvÖöåµæ*Ñ Î�4 å Ì åµæ#Í Ì�Î äùÖ æ�Õ4ÏYÍ Î æ*ÑV;#Ñ0Ö�ÖTÍZâ0Ñ25Ð<Ôõæ:Í ÌIÎ âjÍIÏ3Ð4Ð Î Ï�Í�Ö ÑMæ×ÍIÏ�:PI;Õ�æ#ÍVâjÐTÐ�Ö�æ×Í Ì�Î Ï0ÏTÕ Ì âjÍ�ä3Ñ Ü ÍvâjÍ Î å±ÍP;�ÍZÖ3ÔAÍvÍ Î Ö æ#ÍVÖ.Ô�Ð ä3ÑyÏ$Ö â Ñ3;#Õ#ÖjÑ5Ð Î ÏÑyÏ�Ð Î 2MÑQER:jEn65Û�æ&ÏOá3Ö æ*Ío20Ð<Ô�ÍIÏ$Ö?Ö Ì 25Õ#ÍuÐ�é Ì 2V2�é|ЪÕ#â*Ö Ì 25Ñyä Ì Ö Ñ0Ð Î â Õ Î Ï�:eL"Õ�æ#ÍVä�Í�æ:ÍvâjÑ5Ö ß�4 Õ*â Íøæ Ì Ï Î Í�ÖTÍvâÍ Î å±ÍvÍIä�ÍIä ê :Åô}Ò ÐIé�Öjæ#Íuå±Ð�âjâ ÍIÏ.Ð4Ð Î ä3Ñ Î�4 æ:Í Ì�Î âjÍIÏ3Ð4Ð Î Ï�ÍøÖjÑMæ:Í�é|Ð�â ÌIÎ Ñ�Ö Ì 25Ñ�ä Ì ÖjÑ5Ð Î â Õ Î :

Page 213: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E�E

=TÍvÍ 8pXÑyÏ$Ö Ì�Î å±ÍTI�ålÑR25Ñ Î ä3ÍvâöÏZL XÍ#2 Ì Ñ<I æ&ÏZLE`I���Í Ì ä<=,Ô�Ñ0Ö<å<æqL E7:ÊÛ\ô

ê K :jc\ôK Ì7:öÍwÛÌ Ì7:jc êÍ Ì7:r65ÛD Í�:jE?6c Í�:öÍ�D6 Í�:ÊÌ KÛ Í�:öÍ�Dô Í�:jc Kê E Í�:r65ô

ê ETsutwv Ì�E�E Ì7xÊÛ ê�y E7xdz�zn{ tz�E�EFs|t 6�xr6'D y ERxjE�E�D�}�t

~ âjÑ5ÖjÍA=TÍvÖjÖ�25Ñ Î�4 E7:jc�D

6�þ#7�ÿ|Ü<gCÝ5)�ßU=TÍZÍ 8&ç Ì â Ì�� ÍvÖ ÍvâöÏ�é|Ъâ��?Ð�ä3Í 25Ñ Î�4 Ö æ*Íø�óç Ô>K�K'� 6

|�0� |�

250� |�500� |�

750� |�1000� |�

1250� |�1500� |�

1750� |�2000�|�0

|�2

|�4

|�6

|�8

|�10

|�12

|�14

|�16

|�18

|�20

|�22

Seek Distance (cyl)

See

k T

ime

(ms)

Ø�Ù|ÚW�sÛIÜ<g?Ý|ñ4ß���ç Ô>K�K�� 6�XÑyÏS8HXâ Ñ3�TÍA=TÍvÍ#8 Ô Õ#âf�TÍ

Page 214: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E ê

� �TÍvâ æ#Í Ì äHXÍIÏjå±â Ñ3�#Ö Ñ0Ð Î XÍ 2 Ì � I � ÏZL��Í Ì ä Ô Ð �`�&ÌIÎ ä�I.�Ñ5Ö)L E7:d}�D�z � Ï��Í Ì ä Ô Ð �`�&ÌIÎ ä�IC�?ÑyÏjÏZL E7:dD�D�� � Ï~ âjÑ5ÖjÍ Ô Ð �`�&ÌIÎ ä<I9=ïÍ'�cЪâ(@�é|Ö ÍvâM��Í Ì äWL E7:d� K'�`� Ï~ âjÑ5ÖjÍ Ô Ð �`�&ÌIÎ ä<I���Ð Î#Ó =TÍ'�F~úâ Ñ0Ö Í�L E7:dc ��KF� Ï��Í Ì ä<X�ÑyÏ åOÐ Î#Î ÍÃå±Ö�ç�â Í � Ì â Ì Ö Ñ5Ð Î IC@�é|Ö ÍvâM��Í Ì äWL E7:dE K z � Ï��Í Ì ä<X�ÑyÏ åOÐ Î#Î ÍÃå±Ö�ç�â Í � Ì â Ì Ö Ñ5Ð Î IC@�é|Ö Ívâ>~ âjÑ5ÖjÍ�L E7:dE � c � Ï~ âjÑ5ÖjÍAX�ÑyÏ åOÐ Î#Î ÍÃå±Ö�ç�â Í � Ì â Ì Ö Ñ5Ð Î IS=TÍ'�VÐ�â\@�é|Ö ÍvâM��Í Ì äWL E7: ê c�c � Ï~ âjÑ5ÖjÍAX�ÑyÏ åOÐ Î#Î ÍÃå±Ö�ç�â Í � Ì â Ì Ö Ñ5Ð Î IC�Ð Î#Ó =TÍ'�T~ âjÑ5Ö Í�L E7:dE � c � Ï~ âjÑ5ÖjÍAX�ÑyÏ åOÐ Î#Î ÍÃå±Ö�XÕ#â Ì Ö Ñ0Ð Î I��Ð Î#Ó =ïÍ'�F~úâ Ñ5ÖjÍ�L E7: �?K } � ÏX Ì Ö Ì ç�æ Ì Ï$ÍVç�â Í#� Ì â Ì Ö Ñ0Ð Î E7:dE K D � Ï��Í Ì ä Ô Ð � ��20ÍvÖ Ñ0Ð Î E7:dE�D?6 � Ï~ âjÑ5ÖjÍ Ô Ð � ��20ÍvÖ Ñ0Ð Î E7:dE�D�E � ÏGQÑ5âöÏ�Ö���ÍIÏ�Í#25ÍIå±Ö E7: ê c KF� Ï=TÍIå±Ð Î ä<��ÍIÏ$Í 25ÍIåOÖUIC�Ð Î*Ó =TÍ��F~ âjÑ5ÖjÍIÏ � Î 2 � L E7: ê K } � Ï

6þ#7Bÿ|Ü<g?Ý0,�ß � �TÍvâ æ#Í Ì äHXÍ 2 Ì�� Ï�é|Ð�â��?Ð�ä�Í 25Ñ Î�4 Ö æ#Íu��ç Ô>K�K'� 6VÐ Î Ö æ*ÍA� Ô ��z�D�D�E:Ï � Ï$Ö Í �

� �TÍvâ æ#Í Ì ä`XÍÃÏ å±âjÑV�#ÖjÑ5Ð Î - Ì 25Õ*Í��ÍÃå±Ð Î#Î ÍIå±Ö�ç�âjÍ � Ì â Ì ÖjÑ5Ð Î @�é|Ö ÍZâ��?ÍIä3Ñ Ì ~ âjÑ5ÖjÍ Ô Ð � ��20ÍvÖ Í ER:jD � E � Ï�?Ñ Î Ñ � Õ �*� Ñ � Í õ ͱé|Ъâ ÍP�?ÍIä3Ñ Ì ~úâ Ñ0Ö ÍTI�@�é|ÖjÍvâ Ô Ð �`�&ÌIÎ äWL ER:jc�E�E � Ï�?Ñ Î Ñ � Õ � =TÍIåOÖ Ð�âöÏ[��ÍÃå±ÍvÑV�TÍÃä õ ͱé|Ъâ ÍP�?ÍIä3Ñ Ì ~úâ Ñ0Ö ÍTI9k�s � D?L �?Ñ Î I ê E3áekbL�?Ñ Î Ñ � Õ � =TÍIåOÖ Ð�âöÏ[��ÍÃå±ÍvÑV�TÍÃä õ ͱé|Ъâ ÍP�?ÍIä3Ñ Ì ~úâ Ñ0Ö ÍTI9k�� � DnL ê D

61�#7%�|Ü<g?Ý�� ß0@�ä#ä3Ñ0Ö Ñ5Ð Î4Ì 2�~úâ Ñ0Ö Í � �TÍZâ æ#Í Ì ämX�Í 2 Ì � Ï÷é|Ð�âN�?Ð�ä3Í 20Ñ Î�4 Ö æ#Í&�óç Ô>K�K'� 6O�9� �0� �$�T�� �?� � �<�]�Ã� � �O� ���I� �Q��� ���T���$�)�I�T� � �� 

Page 215: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E K

Actual Simulation

|¡0¢ |¡

5£ |¡

10¢ |¡

15£ |¡

20¢ |¡

25£ |¡

30¢ |¡

35£ |¡

40¢ |¡

45£ |¡

50¢|¤0.00

|¤0.25

|¤0.50

|¤0.75

|¤1.00

Response Time Distribution (ms)

Ø�Ù¤Ú��sÛIÜ<g?ÝyÞ ß- Ì 20Ñyä Ì Ö Ñ5Ð Î ~úÐ�â�8R25Ð Ì ä,��ÍIÏ9�4Ð Î Ï�Í � Ñ � ÍOXÑ�Ï�Ö âjÑV;#Õ*Ö Ñ5Ð Î Ïm�C¥'¦�§ � � � � � �)���T� � � �0�±��$� �I�T�Z¨�©'ª[« �E� �v� �$�)���T� � � �¤�e¬ �_­ ��®?¯�� � � � � �0�±�e°±¨�² �±³�³0� � ���)�I�T� � � ��� ���<� � �$� �e´v�±� � � �Y�­ � ��� �y�I�S� °  

Actual Simulation

|¡0¢ |¡

5£ |¡

10¢ |¡

15£ |¡

20¢ |¡

25£ |¡

30¢ |¡

35£ |¡

40¢ |¡

45£ |¡

50¢|¤0.00

|¤0.25

|¤0.50

|¤0.75

|¤1.00

Response Time Distribution (ms)

Ø�Ù¤Ú��sÛIÜ<g?Ý0)�ß- Ì 20Ñyä Ì Ö Ñ5Ð Î ~úÐ�â�8R25Ð Ì ä,��ÍIÏ9�4Ð Î Ï�Í � Ñ � ÍOXÑ�Ï�Ö âjÑV;#Õ*Ö Ñ5Ð Î Ïm�C¥'¦�§ � � � � � �)���T� � � �0�±�µ � � �$� �Z¨R©'ª[« �Y� �Ã� �$�)�I�T� � � �¤�e¬ �P­ ��®?¯�� � � � � �0�±�e°±¨7² �±³'³(� � �$�)���T� � � ��� �$�<� � �$� �e´Z�Z� � � �Y�­ � ��� �y�I�S� °  

Page 216: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E�z

Actual Simulation

|¡0¢ |¡

5£ |¡

10¢ |¡

15£ |¡

20¢ |¡

25£ |¡

30¢ |¡

35£ |¡

40¢ |¡

45£ |¡

50¢|¤0.00

|¤0.25

|¤0.50

|¤0.75

|¤1.00

Response Time Distribution (ms)

Ø�Ù¤Ú��sÛIÜ<g?Ý0,�ß- Ì 20Ñyä Ì Ö Ñ5Ð Î ~ Ъâ�8R25Ð Ì ä���ÍIÏ9�4Ð Î Ï�Í � Ñ � ÍPXÑ�Ï�Ö âjÑV;#Õ*Ö Ñ5Ð Î Ïo�C¥'¦�§ � �)���T� � � � �Z� �$� ���T��¨©'ª[« �Y� �v� �$�)���T� � � �¤�e¬ �H­ ��®?¯�� � � � � �0�±�e°±¨%² �±³�³T� � ���)�I�T� � � ��� �$�<� � �$� �¶´v�±� � � �Y�`­ � ��� ��y�I�S� °  

Actual Simulation

|¡0¢ |¡

5£ |¡

10¢ |¡

15£ |¡

20¢ |¡

25£ |¡

30¢ |¡

35£ |¡

40¢ |¡

45£ |¡

50¢|¤0.00

|¤0.25

|¤0.50

|¤0.75

|¤1.00

Response Time Distribution (ms)

Ø�Ù¤Ú��sÛIÜ<g?Ý�� ß- Ì 20Ñyä Ì Ö Ñ5Ð Î ~ Ъâ�8R25Ð Ì äH��ÍIÏS�4Ð Î Ï$Í � Ñ � Í\XÑyÏ$Ö â Ñ3;#Õ#ÖjÑ5Ð Î ÏU��¥'¦�§ � �)�I�T� � � �0�±� µ � � ��� ��¨©'ª[« �Y� �v� �$�)���T� � � �¤�e¬ �H­ ��®?¯�� � � � � �0�±�e°±¨%² �±³�³T� � ���)�I�T� � � ��� �$�<� � �$� �¶´v�±� � � �Y�`­ � ��� ��y�I�S� °  

Page 217: Aggressive Centralized and Distributed Scheduling ofDisk Requests

deP�dw·ûPa¸º¹»� _fÿ þ½¼

$¾@�;�;4Ð?��}'&_�0: @U;5;�ÐªÖ ÖZá?¿A: 1óÌ â<å±Ñ Ì�Ó �?Ð�25Ñ Î4Ì á�À�=òåµæ#ÍÃä3Õ�25Ñ Î�4 ��Í Ì 2 Ó�� Ñ � Í � â ÌIÎ Ï Ì å±Ö Ñ0Ð Î Ï.Á�Ñ5ÖjæPXÑyÏS80��ÍÃÏ�Ñ Óä3Í Î ÖiX Ì Ö Ì� áRÃ2ljí'ıà<àfÅ?Æ�Ç�È�ÉAí9ÊM�ÌË4à[Í�Î���ËAÏZÇ7��àtl�Ç����CÆyí?Ç���Рì]í?ÇZÊIà�l<à)Ç�ıà�í?Ç�Ñ�àtl�ÒUÓ%�Ql±È3àYÔo�����UÕ���ÉIàfÉOá@ � Ï$Ö Ívâöä Ì�� á?@Õ 4 Õ4Ï�Ö ê }���}3á����.:�z���D Ó z�}�c7:

$¾@�;�;4Ð?}�E'&_�0:.@U;�;4ÐªÖ Övá%¿A: 1�Ì â<å±Ñ Ì�Ó �?Ð�20Ñ Î4Ì á�À)=�å<æ#ÍIä3Õ�20Ñ Î�4 %�� � ��Í'�òÕ*ÍIÏ�ÖöÏÖÁ�Ñ0Ö æOXÍ Ì ä720Ñ Î ÍIÏOã Ì çQÍvâ Óé|Ð�â �&Ì�Î å±ÍT×a� Ì 25Õ Ì Ö Ñ0Ð Î� á1Ã2ljí'ıà<àfÅ?Æ�Ç�È�É�í9ÊT��Ë4à_Ï�Ø�Ø�Ø,Ù�àf��ÐjÚ Û%Æ�Ü[à_ÝÞÒ É)��àZÜoÉ_ÝÞÒ�ÜUß*í�É#Æ�àRÜøá ð�Ì 8TÍõ Õ#Í Î Ì -�ÑyÏ$Ö Ì á�G%25Ð�âjÑyä Ì á�XÍÃå±Í � ;�ÍZâ ê }�}�E3áq���á: ê�ê z Ó ê K�� :

$ õ�Ì Ö Í'} ê &Pâ_: õ�Ì Ö ÍIÏOáuÑ�ã[ä ÏCå%æºÝÞàRçZÉ#Ò�É)�$à)ÜoÉ'èJæ%ß���Æ�Ü_Æré#Æ�Ç�È�Ã�à�lVÊZíQl�Ü_�?Ç�ıàöá:ç�â ÐIé|ÍIÏ Ï$Ñ5Ð Î Ì 2Cç�â ÍIÏjÏõ ÐTÐ�8*ϱá ê }�} ê :

$ õ Í Î#Î } � &_=�: õ Í Î#Î ÍvÖjÖvá.XA:á�?Í 2yÏS83Ñ.áaÀ�@ Ô 2 Ì Ï Ï Ó�õ�Ì Ï�ÍIäOXÑyÏS8m=�å<æ#ÍIä�Õ�25Ñ Î�4 @U2 4 Ð�âjÑ5Öjæ � ã[ê � ��20Í � Í Î Ö ÌIÓÖ Ñ0Ð Î Ì�Î ä&çQÍvâ$é|Ð�â �&Ì�Î åOÍA=TÖ Õ ä �� á Ô 2 Ì Ï Ï�ç�âjÐ ÍIå±ÖZá�ë Î ÑV�TÍvâöÏ�Ñ5Ö � ÐIéa~qÑ�Ï å±Ð Î Ï�Ñ Î :

$ õ Ñ0Ö Ö�����&ÖXA: õ Ñ0Ö ÖjÐ Î á�ì�:ní�â Ì�� áWÀ�XÑyÏS8�=ïæ Ì ä3Ð'Á�Ñ Î�4? áBÃ~ljí�ıà<àfÅ?Æ�Ç�È�Éüí9Ê1��Ë4à�Í)î��ÌË0Ï)ÇR��à�l)Ç����CÆyí?Ç���Ð�ì]í?ÇZÊIàtlZÚà)Ç�ıà í?ÇuÑ�à�l)ÒAÓ%�QlïÈ�à�Ôo�����FÕ���ÉIàfÉOá ð Ð Î�4&õ Í Ì å<æ�á ÔAÌ 25Ñ�é|Ð�â Î Ñ Ì áq=TÍ �#ÖjÍ � ;4Ívâ ê }�����áq���.:�z�z ê Ó z�z���:

$ õ Ñ0Ö Ö���}�&ÖXA: õ Ñ5ÖjÖ Ð Î áðÀ�@�â � =�å<æ#ÍIä�Õ�25Ñ Î�4 Ñ Î =ïæ Ì ä3Ð'ÁAÍIäñXÑ�Ï98*Ï Â álì[æbòQÃ�ì[æ�ó�áH� Ì â<å<æ ê }���}3á���.: ê z KIÓ ê z�cq:

$ ÔAÌ â Í'��}�&N�^: ÔAÌ âjÍ � áa�0:%ì Ì Õ#æ Ì â Ñ.áa�^: ð ÑV� ÎR� á[À<ç�â Ñ0Ð�â Ñ0Ö � Ñ Î X(� õ =���ÍIÏ$Ð�Õ#âöå±Í�=òåµæ#ÍÃä3Õ�25Ñ Î�4? ábÃ~l í�Úıà<àfÅ?Æ�Ç�È�Écí9Ê_��Ë4àFÍ�Î���Ë<ÏZÇ7�$à�l�Ç5����Æyí?Ç���Ðüì]í?ÇZÊIà�lµàZÇ�ıà�í?ÇôÑ�à�l)ÒõÓö�QlïÈ3à(Ôo�����FÕ���ÉIàfÉOá.@ � Ï$Ö Ívâöä Ì�� á@Õ 4 Õ4Ï�Ö ê }���}�áW���á:�z�}n6 Óï� ê ER:

$ Ô æ*Í Î }�E'&uçY: Ô æ#Í Î áníP:�í�Ñ3;4Ï�Ð Î á?�0: â Ì Öf÷Tá�XP:vç Ì Ö Ö ÍZâ<Ï�Ð Î á�À�@ Î ×a� Ì 25Õ Ì Ö Ñ0Ð Î Ð�éB��ÍIä�Õ Î ä ÌIÎ Ö%@âjâ Ì � Ï�Ð�éXÑ�Ï98*Ï�Õ Ï�Ñ Î54øÌIÎ @ � ä Ì æ�25D���}�E  áqÃ~l í'ıà<àfÅ?Æ�Ç�È�É�í9Ê��ÌË4à(Í�ø?ø7ù(ãuìYòúÝ�Ï'û1òQØAÛqÙ�ÏIìYÝ ì]í?ÇZÊIà�l<à)Ç�ıàí?Çüòùàf��É#àNlµàZÜ[à)Ç7�P�?Ç�Åmòúí'Å3à�ÐeÆ�Ç�Èûí9Êúì]í?ÜUßÞàn�$à�lFÝÞÒ É)��à)ÜoÉOá õ Ð�Õ�2�ä3Ívâvá Ô Ð�20Ð�â Ì ä3Ð*áU� Ì � ê }�}�E3á���.:q6 ��Ó ��D�:

$ Ô æ*Í Î } ê &_=�: Ô æ#Í Î á�ì�:�=TÖ ÌIÎ 8TÐ'�3Ñ�å�áaì�:iâ�Õ#â ÐïÏ�ÍTá>XA: � Ð'Á�Ï920Í � á(À<çsÍvâ�é|Ъâ �&ÌIÎ å±Íõ×ý� Ì 25Õ Ì Ö Ñ5Ð Î ÐIé � ÁAÐ�Í ÁôX�ÑyÏ98H=�å<æ#ÍIä3Õ525Ñ Î54 @U2 4 Ð�âjÑ5Ö æ � ÏQé|Ð�â[��Í Ì 2 ÓC� Ñ � Í(= � Ï�ÖjÍ � Ï Â á�Ù�àf��ÐjÚ#Û%Æ�Ü[à�ÝWÒ�É)�$à)ÜoÉ0þ*í?à3l)Ç���Ð�áÿ]Ð�2C:�z3á��Ð5:�z3á.=TÍ �*Ö Í � ;4Ívâ ê }�} ê á����.:�z�En6 Ó z�z�c7:

$ Ô æ*Í Î } � &_=�: Ô æ#Í Î á?XP: � Ð'Á�Ï920Í � áqÀ)=�åµæ*ÍIä3Õ�20Ñ Î�4øÔ Õ Ï�Ö Ð � ÍvâöÏQÑ Î�Ì �Ð Î#Ó ��Í � Ð'� Ì 25��Í Ì 2 Ó�� Ñ � ÍU= � Ï�ÖjÍ �Á�Ñ5Öjæ Ì�Î @U����20Ñyå Ì Ö Ñ0Ð Î Ö ÐOXÑ�Ï98l=�åµæ*ÍIä3Õ�20Ñ Î�4� ábÙóàf��ÐjÚ Û%Æ�Ü[àTÝÞÒ�É)�$à)ÜoÉõþ#í?àNl�Ç5��Ð�áaÿ]Ð�2�:ic3á��Ð5: ê áì Ì�Î Õ Ì â � ê }�} � á����.:�D�D Ó 6 K :

$ Ô Ð��%6 K &N×[: Ô Ð�� �&Ì�Î á ð :�â(25Ñ � 8TÐ#á õ :R� ��Ì�Î áaÀ�@ Î4Ì 2 � Ï�ÑyÏ]Ð�é>=�å ÌIÎ#Î Ñ Î54 çQÐ�20Ñyå±Ñ0ÍIÏQé|Ð�â���ÍIä3Õ4å±Ñ Î�4 X�ÑyÏ98=TÍvÍ#8 � Ñ � ÍIÏ Â á�Ý�ÏfãUò»þ*í?à3l)Ç���Рí9Ê ì]í?ÜUßÞàn�CÆ�Ç�È�áRÿ�Ð�2�: ê á5�Ð�:Rz�áW=TÍ �*Ö Í � ;4Ívâ ê }?6 K á����.: K c�} Ó�K 6'}7:

K E �

Page 218: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E�D

$¾X Ì�Î Ñ ��z�&T=�:?X ÌIÎ Ñ5Í#2�áR�o:RíÍZÑyÏ�ÖZá.À�ÿ Ó = Ô @(�øã�@ Î @óä Ì �#ÖjÑV�TÍMXÑyÏS8`=�åµæ*ÍIä3Õ�20Ñ Î�4 @�2 4 Ъâ Ñ0Ö æ �H ánÃ~ljí�ıà<àfÅ�ÚÆ�Ç�È�É~í9ÊQ�ÌË4à`ÏfØbØ�Ø Ï)Ç7�$à�l)Ç����CÆyí?Ç���Ð��CíQl��#É�Ë*í�ß,æ[Ç ì]í?ÜUßÞàn�$à�lpÝWÒ�É)�$à)ÜoÉ�æ2lïÈ?�?Ç5Æré#����Æyí?Ç3á��Í#Á� â�20Í Ì�Î ÏOá ð Ð�Õ#Ñ�Ï�Ñ Ì�Î4Ì áq� Ì â<å<æ ê }���z3á����.:�}�c Ó ê E�zR:

$¾X�Í Î#Î c?6 &uçY:iXÍ Î#Î Ñ Î�4 á(À�×���ÍÃå±Ö<ÏYÐ�éP=�åµæ*ÍIä3Õ�20Ñ Î�4 Ð Î GQÑV20Í`�?Í � Ð�â � � ��ÍZâ Ì ÖjÑ5Ð Î Ï Â á1Ã2ljí'ıà<àfÅ?Æ�Ç�È�É×í9Ê��Ë4àAã��iÏ�Ã�ÝmÝ�ßml�Æ�Ç�ÈQþ#í?Æ�Ç7�Yì]í?ÜUßÞà?�$à�l:ì]í?ÇZÊIà�l<à)Ç�ıà<á.@�Ö�2 Ì�Î Ö Ñ�å Ô Ñ0Ö � áq��Í Á ì�Ívâ<Ï$Í � áÞ@U�#â Ñ32 ê }�c?6Tá���.:�} Ó�K ê :

$¾×a;�20Ñ�} � &P�^:�×a;�25Ñ Î�4 áÞ�^:ö= Ì Ö ��Ì�Î4Ì â Ì ��Ì�Î Ì�Î á�À�= ��Î �Uí�Í Î ãM@ Î ×��Ö Í Î Ï$ÑV;�20ÍPGQÑV20ÍA��ͱé|ÍvâjÍ Î å±Í_í�Í Î ÍZâ Ì�ÓÖ Ðªâ  áöÃ~l í'ıà<àfÅ?Æ�Ç�È'Éuí9Ê0��Ë4à(ãuìYòºÝÞÆjÈ�Ü[à���l)Æ�ÄZÉ ì]í?ÇZÊIà�lµàZÇ�ıàVí?Ç`òùàf��É#àNlµà)Ü[àZÇ7�[�?Ç�ÅFò~í�Å3à�ÐeÆ�Ç�È&í9Êì]í?ÜUßÞà?��à�l(ÝÞÒ�É)�$à)ÜoÉOá�� Ì Ï�æR�3Ñ32V20ÍTá � Í Î*Î ÍIÏ Ï$ÍvÍTá5� Ì�� ê }�} � á����.: ê E�� Ó ê�ê 6?:

$¾G#â Ì�Î c�}�&P¿A:%G#â Ì�Î 8�á�À�@ Î4Ì 2 � Ï�Ñ�Ï ÌIÎ ä � �#ÖjÑ � Ñ3÷ Ì ÖjÑ5Ð Î ÐIé�XÑ�Ï98l=TÖ Ðªâ Ì'4 ÍHXÍ#�3Ñ�å±ÍIÏ�é|Ъâ � Ñ � Í Ó =ïæ Ì âjÑ Î�4= � Ï�ÖjÍ � Ï Â á�þ*í?à3l)Ç���Ð*í9Ê[��Ë4à1ãUÉ�ÉZí'Ä Æ����CÆyí?Ç�ÊZíQl�ì]í?ÜUßÞà?��Æ�Ç�ÈoòO�?ÄZË5Æ�Ç4à�l�ÒIá�ÿ]Ð�2C: ê c�á7��Ð�: � á � å±Ö Ð�;�ÍZâê }�c�}�áq���.:�c�E K�Ó c K E7:

$¾G#Õ Ñ } ê &AG#Õ Ñ0Ö<Ï$Õ ð Ñ � Ñ5ÖjÍIä�á�À�� K c K�K =�W��� K c K zn=����'� K c K�� =��ôê Î Ö Í#2V25Ñ 4 Í Î ÖPXÑyÏS8|Xâ Ñ3�TÍIÏ Ô ×*� Ì�Î#ÓÕ Ì 2  áq=���ÍÃå±Ñ�  å Ì Ö Ñ0Ð Î �Õ � ;4Ívâ � ê Ga¿\c���c���× Ó E ê á5ì�Õ�2 � ê }�} ê :

$¾G#Õ Ñ } ê Ì &PG#Õ Ñ5ÖöÏ�Õ ð Ñ � Ñ0Ö ÍIä á7À�� K c K�K =���'� K c K z?=���'� K c K'� =��Tê Î ÖjÍ 2V20Ñ 4 Í Î ÖÞXÑ�Ï980X�â ÑV�TÍÃÏ � ×��w� Ì�Î#ÓÕ Ì 2 Ó = Ô =Rê ð Ð 4 Ñyå Ì 2�=?�4ÍIå±Ñ� �å Ì ÖjÑ5Ð ÎB áq=?�4ÍIå±Ñ�  å Ì Ö Ñ5Ð Î �Õ � ;�ÍZâ � ê Ga¿\D�E�D?6'× Ó E ê á�ì ÌIÎ Õ Ì â � ê }�} ê :

$¾G#Õ Ñ } ê ;�&PG Õ Ñ5Ö<Ï$Õ ð Ñ � Ñ5Ö ÍÃä�á7À�� K c K�K =���'� K c K zn=���'� K c K�� =��Nê Î Ö Í#2V25Ñ 4 Í Î ÖÞXÑyÏS80XâjÑV�TÍIÏ � ×�� � Ì�Î#ÓÕ Ì 2 Ó =���ÍÃå±Ñ�  å Ì Ö Ñ0Ð Î Ï�� ê Î Ï$Ö Ì 232 Ì Ö Ñ5Ð Î� áq=���ÍÃå±Ñ�  å Ì Ö Ñ0Ð Î �Õ � ;4Ívâ � ê Ga¿(D�E�D�D�× Ó E ê @[á�ì�Õ Î Í ê }�} ê :

$¶í ÌIÎ�4 }�z Ì &`íP:�í ÌIÎ�4 ÍZâvá õ :%~ Ъâ Ö æ*Ñ Î�4 Ö Ð Î á1�0:�¿Ð�Õ�á�_:�ç Ì Ö ÖZáoÀ�XÑyÏS8 =TÕ�;4Ï � Ï$Ö Í � ð Ð Ì ä õ�Ì 2 Ì�Î å ÓÑ Î54 ã0XÑ�Ï98^=TÖjâ ÑV�*Ñ Î�4 �*Ï�: Ô Ð Î �TÍ Î ÖjÑ5Ð Î4Ì 2�X Ì Ö Ì ça2 Ì å±Í � Í Î Ö Â á.Ã2ljí'ıà<àfÅ?Æ�Ç�È�É�í9ÊN�ÌË4à����'�ÌË��Ö��a�?Æ�ÆÏ)ÇR��à�l)Ç����CÆyí?Ç���Ðuì]í?ÇZÊIà�lµàZÇ�ıàCí?ÇüÝÞÒ�É)�$à)ܺÝÞÄ Æ¤àZÇ�ıà�ÉOá[~ Ì ÑV20Í Ì á>¿ Ì Á Ì Ñ5Ñ�á�ì ÌIÎ Õ Ì â � ê }�}�z�á[ÿ�Ð�2�: ê á���.: � E Ó±� }�:

$¶í ÌIÎ�4 }�z�&FíP:�í Ì�Î�4 Ívâvá��_:Tç Ì Ö ÖZáYÀ � æ*Í�ç�â Ð�åOÍIÏ Ï Ó GY20Ð'Áô�?Ð�ä3Í 2�ãi×� Ì'� Ñ Î Ñ Î�4 ê�� � çQÍvâ�é|Ъâ �&ÌIÎ å±Í]é|â Ð �Ö æ*ÍF= � Ï�ÖjÍ ��� ÏAçQÐ�Ñ Î Ö�ÐIé�ÿ�Ñ0Í Á  áqÃ~l í'ıà<àfÅ?Æ�Ç�È'ÉYí9ÊP��Ë4à_Í�ø?ø�õãuìYò»Ý�Ï�ûMòQØPÛqÙUÏÃìYÝûì]í?ÇZÊIà�l<à)Ç�ıàí?Çoòùàf��É#àNlµàZÜ[à)Ç7�.�?Ç5Å\ò~í'Å3à�ÐeÆ�Ç�Èuí9Êóì]í?ÜUßÞàn�$à�lýÝWÒ�É)�$à)ÜoÉOán= Ì�Î Ö Ì�Ô 2 Ì â Ì á ÔAÌ 20Ñ é|Ð�â Î Ñ Ì á�� Ì � ê }�}�z3á���.:���c Ó }n6�:

$¶í ÌIÎ�4 } � &FíP:aí Ì�Î�4 Ívâvá õ :q~úÐ�â Öjæ#Ñ Î54 Ö Ð Î áa�0:%¿Ð�Õ�á��N:�ç Ì ÖjÖvá[À�X�ÑyÏ98O@�â â Ì � ϱã0¿Ñ 4 æ Ó çQÍvâ$é|Ð�â �&Ì�Î åOÍTá¿Ñ 4 æ Ó ��Í#25Ñ Ì ;#ÑV20Ñ5Ö � =TÖjÐ�â Ì'4 ÍO=TÕ�;4Ï � Ï$Ö Í � Ï Â á[Ï�Ø�Ø�Øîì]í?ÜUßÞàn�$à�l<ábÿ]Ð�2�: K 6ïá[�Ð5:�z3á[� Ì â<å<æ ê }�} � á���.:�z�E Ó z�c�:

$¶í�ÍvÑ�Ï��?6 &P�o:.í�ÍvÑyÏ$ÖváY=B:.X Ì�Î Ñ5Í 2.ábÀ�@ Ô Ð Î Ö Ñ Î Õ#Õ � ÐIé[X�ÑyÏ98O=�å<æ#ÍIä3Õ�20Ñ Î�4 @U2 4 Ð�âjÑ5Öjæ � Ï Â áöãuìYò Û�lf�?ÇnÉ)Ú�?Ä��CÆyí?ÇnÉ í?Çùì]í?ÜUßÞàn�$à�lUÝÞÒ É)��à)ÜoÉOá�ÿ]Ð�2C:�D3á���Ð�: ê á�G#Í ;*â Õ Ì â � ê }��n6ïáW�5�.:q6�6 Ó } K :

$¶í�ÍvÑ�Ï��?6 Ì &P�0:bí�ÍvÑ�Ï�Övái�o:i��Í �3Î Ð�2yä#ÏOáa×[:�ç�Ñ0Ö Ö Ì â<ä�á(À�XÑyÏS8ü=òåµæ#ÍÃä3Õ�25Ñ Î�4 Ñ Î = � Ï$Ö Í � ÿ  ábÃ~l í'ıà<àfÅ?Æ�Ç�È'Éí9Ê���Ë4àHãuìYò Ý�Ï'û1òQØAÛqÙ�ÏIìYÝ ì]í?ÇZÊIà�l<à)Ç�ıàúí?Çüò�àf��É#à3l<à)Ü[à)Ç7�T�?Ç�Å^òúí'Å3à�ÐeÆ�Ç�È í9Ê�ì]í?ÜUßÞà?��à�lÝÞÒ É)��à)ÜoÉOá õ�ÌIÎ ��áq@�2V;4Ívâ Ö Ì á5� Ì�� ê }��?6Tá����.:�D�} Ó c��7:

$¶í�ÍvÑ�Ï�}�D�&P�o:�íÍZÑyÏ�ÖZá(ì�:1~úÍIÏ$Ö Ì 232�á_À�X�ÑyÏ98�=òåµæ#ÍÃä3Õ�25Ñ Î�4 Ñ Î ð Ñ Î Õ��  á(Ã2ljí'ıà<àfÅ?Æ�Ç�È�Éúí9Ê�ÌË4à�ì]í?ÜUßÞà?��à�lòùàf��É#àNlµàZÜ[à)Ç7�aû5ljí?à�ß��jìYòlû��uì]í?ÇZÊIàtlµà)Ç�ıàöá � â�2 Ì�Î ä�Ð#á�GY25Ъâ Ñyä Ì á'XÍIåOÍ � ;4Ívâ ê }�} � á����.:q6�z�} Ó 6 � c�:

Page 219: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E�c

$¶í�ЪÖ�2ï6�z�& Ô :aí�Ð�Ö�20Ñ5Í ;�ábíP:%� Ì å ×aÁ�Í Î á[À<çQÍvâ$é|Ð�â �&Ì�Î åOÍVÐ�é��?Ð'� Ì ;525Í Ó ¿Í Ì ämXÑ�Ï98^=TÖjÐ�â Ì�4 ÍpXÍ ��Ñyå±ÍIÏ Â áþ*í?à3l)Ç���Ð�í9ÊH��Ë4à`ãUÉ�ÉZí'Ä Æ����CÆyí?ÇpÊZíQl�ì]í?ÜUßÞà?��Æ�Ç�ÈmòO�?ÄZË5Æ�Ç�àtl�ÒIábÿ]Ð�2C: K E�á[�Ð�: � á � å±Ö Ð�;4Ívâ ê }n6�z3á���.:�c�E �ªÓ c K zq:

$¶í�â Ì�� }�E'&Pì�:qíâ Ì � á õ :5¿Ð�âöÏ�Övá��^:R~ Ì 2V8TÍvâZáYÀöç Ì âjÑ5Ö � =ïÖ â Ñ3�#Ñ Î54 Ð�ébXÑyÏS8`@âjâ Ì � ϱã ð Ð'Á Ó�Ô ÐïÏ�Ö0��Í 20Ñ Ì ;525Í=TÖjÐ�â Ì'4 Í[Á�Ñ0Ö æ_@óåvå±Í �#Ö Ì ;�20Í � æ#âjÐ�Õ 4 æ��#Õ#Ö Â á�Ã~l í'ıà<àfÅ?Æ�Ç�È�ÉAí9Ê>��Ë4àUÍ�'��Ë0Ï)Ç7�$à�l)Ç����CÆyí?Ç���Ð�ì]í?ÇZÊIà�l<à)Ç�ıàí?ÇuÑ�à�l)Ò�Óö�QlïÈ3à[ÔP���C��Õ���ÉIàfÉOá õ â ÑyÏS; Ì�Î ÍTá�@Õ4Ï$Ö â Ì 25Ñ Ì á�@�Õ 4 Õ4Ï$Ö ê }�}�E3á����.: ê � � Ó ê c ê :

$¾¿�Í Î 2���}�&0�^:�¿�Í Î 25Í � á õ :���å �Õ#ÖjÖvá(À�XU@o=nXñê�� � Ô æ Ì â Ì å±Ö ÍvâjÑyÏ$Ö ÑyåZϱãQ@ Ô Ð � � Ì â ÑyÏ$Ð Î Ð�éP�<ÿA=úÖjÐÿ0�  áoÃ~l í'ıà<àfÅ?Æ�Ç�È�É�í9Ê���Ë4à ì]í?ÜUßÞà?�$à�l òùàf��É#àNlµàZÜ[à)Ç7��û5l í?à ß �jìYò û�� ì]í?ÇZÊIà�lµàZÇ�ıà<á_��Í Î Ð*á�Í � Ì ä Ì á�XÍÃå±Í � ;�ÍZâ ê }���}3á����.:ÞD�c�c Ó D?6'��:

$¾¿�Ð�2V2 } K &0�^:q¿�Ð�2V2 Ì�Î ä áöíP:.íÑ3;4Ï�Ð Î á1Àöç Ì âjÑ5Ö � XÍIå�20Õ4Ï�ÖjÍvâ Ñ Î�4 é|Ъâ Ô Ð Î Ö Ñ Î Õ*Ð�Õ4Ï � �4Ívâ Ì Ö Ñ0Ð Î Ñ Î ��ÍIä3Õ Î#Óä ÌIÎ ÖHX�ÑyÏ98|@âjâ Ì � Ï Â á�Ã2ljí'ıà<àfÅ?Æ�Ç�È�É í9Ê<��Ë4àQÎ���ËüÏZÇ7�$à�l�Ç5����Æyí?Ç���Ð ì]í?ÇZÊIà�lµàZÇ�ıàCí?Çüãgl�ÄZË5ÆV�$àfÄ��Cà3lf��ÐÝÞà ß?ß*íQlZ�aÊZíQlFÃ~l í�ÈQl��?Ü_Ü_Æ�Ç�È�Ó%�?Ç�È�à7� È3àfÉ��?Ç5Å]æ%ß�àtl����CÆ�Ç�È ÝÞÒ É)��àZÜoÉOá õ ÐTÏ$Ö Ð Î á[� Ì ÏjÏ Ì å<æ�Õ4Ï�ÍvÖjÖ<ÏOá� å±Ö Ð�;4Ívâ ê }�} K á����.: K z Ó z�D7:

$¾¿�Ð�Õ�}�z�&P�o:M¿Ð�Õ�á!�N:�ç Ì Ö ÖZá`À � â Ì ä�Ñ Î�4 XÑyÏS8 ÔAÌ � Ì å±Ñ0Ö � é|Ð�âCçQÍvâ$é|Ð�â �&Ì�Î åOÍ Â á(Ã~l í'ıà<àfÅ?Æ�Ç�È�É í9Ê�ÌË4à�RÇ�Å ÏZÇ7�$à�l�Ç5����Æyí?Ç���Ð�ÝÞÒ�ÜUß*í�É#Æ�àRÜ�í?Ç"�ÖÆjÈ�ËRÚïÃ�à�lVÊZíQl�Ü_�?Ç5ıàFÔPÆrÉ)�1l�Æ�ç#àn�$àfÅ ì]í?ÜUßÞà?�CÆ�Ç�È�á1=?�4Ð�8 ÌIÎ ÍTá~ Ì Ï�æ*Ñ Î�4 Ö Ð Î áqì�Õ�2 � ê }�}�z�áW���á: K c�z Ó�K 6'ER:

$¾¿óçb} K &P¿Í Á[20ÍvÖ Ö Ó ç Ì å�8 Ì â<ä Ô Ð � � Ì�ÎR� áqÀ�¿�ç Ô>K�K�� E_=TÍvâjÑ5ÍIÏazR:jD Ó Ñ Î åµæH= Ô =Rê ÓCK XÑyÏS8TXâ Ñ3�TÍTá � ÍIå<æ Î Ñ�å Ì 2��ͱé|Ívâ Í Î å±Í0� ÌIÎ Õ Ì 2  á4ç Ì âjÖ��Õ � ;�ÍZâ[D�}�c�E Ó ��z � c�á%×�ä�Ñ5Ö Ñ0Ð ÎQK á�@��#â Ñ32 ê }�} K :

$¾¿óçb} K�Ì &A¿�Í Á[25ÍvÖjÖ Ó ç Ì å�8 Ì âöä Ô Ð � � ÌIÎ7� á^À�¿�ç Ô>K�K'��� � � D?� � c7� � 6*zR:jD Ó Ñ Î åµæ = Ô =Rê ÓCK XÑyÏS8 Xâ Ñ3�TÍTá� ÍIåµæ Î Ñyå Ì 2.��ͱé|ÍvâjÍ Î å±Í0� ÌIÎ Õ Ì 2  á4ç Ì âjÖ��Õ � ;4Ívâ>D�}�c�E Ó ��z � c#á.×]ä3Ñ0Ö Ñ5Ð Î z�áq=TÍ �#ÖjÍ � ;4Ívâ ê }�} K :

$¾¿óçb}�z�&P¿Í Á[20ÍvÖ Ö Ó ç Ì å�8 Ì â<ä Ô Ð � � ÌIÎ7� á�À�¿�ç Ô>K'� }�E�@½z7:dD Ó Ñ Î å<æ�= Ô =Rê ÓCK XÑyÏS8ôXâ Ñ3�TÍIϱá � ÍIå<æ Î Ñ�å Ì 2��ͱé|Ívâ Í Î å±Í0� ÌIÎ Õ Ì 2  á4ç Ì âjÖ��Õ � ;�ÍZâ[D�}�c ê Óï� z�D�}�á%×�ä�Ñ5Ö Ñ0Ð Î z3áq=ïÍ �#Ö Í � ;4Ívâ ê }�}�zR:

$¾¿óçb} � &P¿Í Á[20ÍvÖ Ö Ó ç Ì å�8 Ì â<ä Ô Ð � � ÌIÎ7� á�À�¿�ç Ô z�z K z�@½z7:dD Ó Ñ Î å<æ�= Ô =Rê ÓCK XÑyÏS8ôXâ Ñ3�TÍIϱá � ÍIå<æ Î Ñ�å Ì 2��ͱé|Ívâ Í Î å±Í0� ÌIÎ Õ Ì 2  á4ç Ì âjÖ��Õ � ;�ÍZâ[D�}�c KIÓ c � D K á%×�ä�Ñ5Ö Ñ0Ð ÎQK á�@��#â Ñ32 ê }�} � :

$¾ì Ì å±Ð?} ê &NXA:aì Ì å±Ð�;4Ï$Ð Î á>ì�:Y~qÑ32V8TÍIÏOáUÀ�XÑyÏS8ü=�å<æ#ÍIä�Õ�25Ñ Î�4 @U2 4 Ъâ Ñ5Öjæ � Ï õ�Ì Ï$ÍIä Ð Î ��Ð�Ö Ì ÖjÑ5Ð Î Ì 2�çQÐïÏ�Ñ ÓÖ Ñ0Ð Î� á�¿Í Á[20ÍvÖ Ö Ó ç Ì åZ8 Ì â<ä � ÍÃåµæ Î Ñyå Ì 2q��Í �4Ð�âjÖváÞ¿�ç ð�Ó�Ô =òç Ó } ê Ó 6ïá.G#Í ;#âjÕ Ì â � ê }�} ê :

$¾â Ì Ö�÷'��}�&P�o:d¿A:�â Ì Öf÷TáUíP:j@A:[í�ÑV;4Ï$Ð Î á�XA:d@A:]ç Ì Ö Ö ÍZâ<Ï�Ð Î á_À�XÑ�Ï98u= � Ï�ÖjÍ � @â<å<æ#Ñ5ÖjÍIå±ÖjÕ#â ÍIÏ�é|Ð�âõ¿Ñ 4 æçQÍvâ$é|Ð�â �&Ì�Î åOÍ Ô Ð � �#Õ*Ö Ñ Î54? á1Ã~ljí�ıà<àfÅ?Æ�Ç�È�É�í9Êõ�ÌË4à_ÏfØbØ�ØAáYÿ]Ð�2�:a6�6ïá��Ð�: ê K á�XÍIå±Í � ;4Ívâ ê }���}3á���.: ê � ��K�Ó ê ��D���:

$¾â�Ñ � ��c'&(�^:0â�Ñ � á`À�= ��Î å<æ#â Ð Î ÑV÷vÍÃä�X�ÑyÏ98 ê Î Ö ÍZâ�25Í Ì ��Ñ Î54? áAÏfØ�ØbØ Û&l��?Ç?É#�?Ä���Æyí?Ç?É í?Ç ì]í?ÜUßÞà?��àtl�ÉOáÿ]Ð�2C: Ô]Ó z�D#á��Ð�: ê�ê áÞ�Ð'�TÍ � ;4Ívâ ê }���c�áq���.:�}?6'� Ó }����7:

$¾â�Ñ � } ê &U~,:�â�Ñ � á7ì�:�=Tâ Ñ3� Ì Ï�Ö Ì � Ì ábÀ�× Î æ Ì�Î å±Ñ Î�4 ��Í Ì 2 ÓC� Ñ � Í\X õ �m=×çQÍvâ$é|Ð�â � Ì�Î å±Í�Á�Ñ5ÖjæQ�?Õ�25ÖjÑV�TÍvâ ÓÏ�Ñ0Ð Î X Ì Ö ÌùÌ�Î ä ç�â Ñ5Ъâ Ñ0Ö � õ�Ì Ï�ÍÃäüX�ÑyÏ98u=�å<æ#ÍIä�Õ�25Ñ Î�4? á1Ã2ljí'ıà<àfÅ?Æ�Ç�È�ÉCí9ÊH��Ë4à`Ï�Ø�Ø�Ø*Ù�àf��ÐdÚ Û%Æ�Ü[àÝÞÒ É)��à)ÜoÉ0ÝÞÒ�ÜUß*í�É#Æ�à7Üøá�= Ì�Î @ Î ÖjÐ Î Ñ0Ð#á � Í#� Ì ÏOá�XÍIå±Í � ;4Ívâ ê }�} ê áq���.: K�K�K�ÓCK z ê :

$ ð�Ì â � }�D'&_�0: ð�Ì â � á�=TÖ Ðªâ Ì'4 Í0@âöåµæ*Ñ5Ö ÍÃå±Övá?X�Ñ 4 Ñ0Ö Ì 2q×��TÕ#ÑV� � Í Î Ö Ô Ðªâ��4Ð�â Ì Ö Ñ0Ð Î á çQÍvâöÏ�Ð Î4Ì 2 Ô Ð �õ� Õ Î Ñyå ÌIÓÖ Ñ0Ð Î á�� Ì � ê }�}�D7:

Page 220: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E?6

$ ð ÍZÍ'}�E'&A×[: ð ÍvÍïáaÀ�=TÐIé|Ö9Á Ì âjÍ ÌIÎ ä?çsÍvâ�é|Ъâ �&ÌIÎ å±Í\ê�ÏjÏ�Õ#ÍÃÏ�Ñ Î Ö æ#ÍPê � ��20Í � Í Î Ö Ì ÖjÑ5Ð Î ÐIé Ì ��@(êSX ç�âjÐ�Ö Ð ÓÖ � �4Í Â á���Í#��Ъâ Ö\�Ð�:5ë ÔAõ � Ô =nX }�E?�'D?6'z3ááë Î ÑV�TÍZâ<Ï�Ñ0Ö � Ð�é ÔAÌ 25Ñ�é|Ð�â Î Ñ Ì á õ Ívâ�8TÍ 20Í � á?� Ì � ê }�}�E7:

$ ðq��Î å�6 K &0~,: ðq�3Î åµæ�áÞÀ�XÐNXÑyÏS8T@â � Ï%�?Ð'�TÍ%$  á7Ã�à�lVÊZíQl)Ü_�?Ç�ıà1Ø'& ��ÐeàR����Æyí?Ç`Ù�à(&#Ƥà(�Qá7ÿ]Ð�2�: ê á���Ð�: � áXÍIåOÍ � ;4Ívâ ê }n6 K áq���.:�z Ó ê c7:

$¾� Ì �3Ö�} K &A� Ì �3ÖjÐ�â Ô Ð�âf��Ъâ Ì Ö Ñ5Ð Î ámÀ��*) ��Ó ê K�� En= ç�â Ð�ä�Õ4å±Öl=?�4ÍIå±Ñ� �å Ì ÖjÑ5Ð Î ÌIÎ ä � ×�� � ÍIå<æ Î Ñ�å Ì 2� Ì�Î Õ Ì 2  á�X�Ð�å±Õ � Í Î Ö ê E K ��E ��� á%��Í �3Ñ�Ï�Ñ0Ð Î @øá���Ð��TÍ � ;4Ívâ ê }�} K :

$¾��å#�Õ���c'& õ :���å#�Õ#Ö ÖZá.À�@ Î × � �#Ñ0â Ñyå Ì 2q=TÖjÕ4ä � Ð�éiÿ Ì â Ñ Ì ÖjÑ5Ð Î Ï�Ñ Î X�@o=RXðÿ]Ð�25Õ � Í\@�å±ÖjÑV��Ñ5Ö �5 á7Ã~l í�Úıà<àfÅ?Æ�Ç�È�É í9Ê0��Ë4à�ì]í?ÜUßÞà?��à�l(òùàf��É#àNlµà)Ü[àZÇ7��û�ljí?à�ß+�jìYòlû��Cì]í?Ç�ÊIà�lµà)Ç5ıà<á ê }���c3áÞ���.: K 6 ��ÓCK ��zW:

$¾�?ÍZâ Ö�6�E�&P@A:��?ÍvâjÖ Í Î ábÀ)=TÐ � Í-,�Õ Ì�Î Ö Ñ0Ö Ì ÖjÑV�TÍ � ÍIåµæ Î Ñ��TÕ#ÍIÏ�é|Ъâ0GQÑV20Í � â 4TÌIÎ ÑV÷ Ì Ö Ñ0Ð Î� á�ç�æ.:jXA: � æ#ÍIÏ$ÑyÏOá� ÍIåµæ Î Ñyå Ì 2.��Í �4Ð�âjÖ(�Ð5: ê D3áÞë Î ÑV�TÍZâ<Ï�Ñ0Ö � Ð�éi~qÑyÏ åOÐ Î Ï$Ñ Î�Ô Ð � �*Õ#Ö Ñ Î�4:Ô Í Î Ö ÍvâZá ê }?6'ER:

$¾� 4 } ê &_=�:%� 4 á�À�ê � �#âjÐ���Ñ Î54 X�ÑyÏ98úçsÍvâ�é|Ъâ �&ÌIÎ å±Í_ÿ�Ñ Ì ð�Ì Ö Í Î å � ��ÍIä3Õ å±Ö Ñ0Ð Î� áýÏfØ�ØbØ Û�lf�?ÇnÉ#�?Ä��CÆyí?ÇnÉí?Çùì]í?ÜUßÞà?��à�l�ÉOá�ÿ]Ð�2C: � E�á��Ð�: ê á�ì Ì�Î Õ Ì â � ê }�} ê á����.: K�K�Ó z�E7:

$ ç Ì Ö Ö����'&AXP:�ç Ì ÖjÖ ÍvâöÏ�Ð Î áaíA:%íÑ3;4Ï�Ð Î á%�o:áâ Ì Ö�÷Tá>À�@ ÔAÌ Ï$Ícé|Ъâ0��ÍIä3Õ Î ä Ì�Î ÖA@�â â Ì � Ï�ÐIé�ê Î Í#�R�4Í Î Ï$ÑV�TÍXÑ�Ï98*Ï�IC�U@\ê9X0L  á.Ã~l í'ıà<àfÅ?Æ�Ç�È�É í9ÊN�ÌË4àAãuìYò Ý�Ï�û1òlæbÔ Ï)Ç7�$à�l)Ç����CÆyí?Ç���Ð�ì]í?ÇZÊIà�lµàZÇ�ıà�í?Ç ò �?Ç7Ú� È3à)Ü[àZÇ7��í9Ê0ÔP������á Ô æ#Ñyå Ì�4 Ð*áqê�2325Ñ Î Ð�ÑyÏOáR� Ì�� ê }����3á����.: ê E�} Ó ê�ê c7:

$ çsÐ�2 � }�z'& Ô :]çQÐ�2 � ÷vЪÑyÏOá1@A: õ æ*Ñyä3ÍTá>XA:>XÑ Ì Ï±áAÀ�XÑyÏS8|�?Ñ5â âjÐ�âjÑ Î�4 Á�Ñ0Ö æu@�25Ö ÍZâ Î4Ì Ö Ñ Î54 Xͱé|Ívâjâ ÍIälëU� Óä Ì Ö ÍIÏ Â áUÃ~l í'ıà<àfÅ?Æ�Ç�È'É&í9ÊQ��Ë4à<Í�ø���Ë^Ï)Ç7�$à�l)Ç����CÆyí?Ç���Ðøì]í?Ç�ÊIà�lµà)Ç5ıàCí?Ç*Ñ�à�l)ÒÓö�QlïÈ3à_ÔP���C� Õ���ÉIàfÉOáXÕ�;525Ñ Î á�ê¿âjÍ 2 ÌIÎ ä�á ê }�}�z3á����.:�c�E ��Ó c ê 6?:

$.,�Õ ÌIÎ }�z'&/,�Õ ÌIÎ ÖjÕ � Ô Ðªâ��4Ð�â Ì Ö Ñ0Ð Î áaÀöç�â Ð?X�â ÑV�TÍ(6�E�E?� ê E�D�E?� ê K?K D?=&ç�â Ð�ä�Õ4å±Ö>� Ì�Î Õ Ì 2  á�ç�Õ�;�20Ñyå Ì Ö Ñ5Ð Î�Õ � ;4Ívâ[� ê Ó ê E K�� ��E Ó E K á%� Ì âöåµæ ê }�}�z7:

$¾� Ì�� Ì } K &Pâ�:Þ� Ì��&Ì 83âjÑyÏ�æ Î4Ì�Î á�çY: õ Ñ�Ï9Á Ì Ï±á.�0:.â Ì âjÍIä72 Ì á1À�@ Î4Ì 2 � Ï$ÑyÏÐIé�GQÑ325ÍNê�� � � â Ì å±ÍIÏ�Ñ ÎúÔ Ð �:Ó� Ívâöå±Ñ Ì 2 Ô Ð � �*Õ#Ö Ñ Î�4 × Î ��Ñ5â Ð Î�� Í Î Ö<Ï Â á.Ã~l í'ıà<àfÅ?Æ�Ç�È�Écí9Ê_��Ë4à`Í�ø?ø%�<ãuìYò Ý�Ï'û1ò<ØPÛqÙ�ÏIìYÝ �?Ç�ÅÃ�Ø�Ù��MæbÙ�ò<ã�óVìYØ10 ø%�oÏZÇ7��àtl�Ç����CÆyí?Ç���Ð�ì]í?Ç�ÊIà�lµà)Ç5ıà�í?ÇNò�àf��É#à3l<à)Ü[à)Ç7�%�?Ç5ÅÖòúí'Å3à�жÆ�Ç�Èøí9Ê÷ì]í?ÜAÚßÞà?��à�l(ÝÞÒ�É)�$à)ÜoÉOá��Í#Á[��Ъâ ÖZá���æ#Ð�ä�Í_ê$Ï92 Ì�Î ä�á�ì�Õ Î Í ê }�} K á����.:q6�� Ó }�E7:

$¾��Í ��Î ���'&P�o:Þ��Í �3Î Ð�2yä#ÏOá1À�=ïÍIå±Ö Ъâ Ó.õ�Ì Ï$ÍIä�XÑyÏS8m=�å<æ#ÍIä�Õ�25Ñ Î�4 Ñ Î Ö æ#ÍTë\�(ê2)!354w= � Ï$Ö Í � ÿ × Î ��Ñ5âjÐ Î#Ó� Í Î Ö Â áYÃ~l í'ıà<àfÅ?Æ�Ç�È�É×í9ÊT��Ë4à_ãuìYò Ý í?à?��Ë4àf��É)��à�l)ÇmÙ�à±È?Æyí?Ç5��Ð�ì]í?ÇZÊIà�l<à)Ç�ıà<á��?Ð�;#ÑV20ÍTá.@U2 Ì ; Ì'�&Ì á@U�#âjÑV2 ê }��?6Táq�5�.:�c � � Ó c�D K :

$¾��Õ#Í � }�z�& Ô :1��Õ#Í �`� 2 ÍZâváaì�:�~qÑV238TÍIϱá0À�ë\�(ê2)!354»X�ÑyÏ98|@�åZå±ÍIÏ Ï�ç Ì Ö Ö ÍZâ Î Ï Â á(Ã~l í'ıà<àfÅ?Æ�Ç�È�ÉCí9Êp�ÌË4à�<Æ�ÇR��à�l�6öÝ5Øbó�ÏSäîì]í?ÇZÊIà�l<à)Ç�ıà<á.= Ì�Î XÑ5Í 4 Ð#á ÔAÌ 25Ñ�é|Ð�â Î Ñ Ì á5ì Ì�Î Õ Ì â � ê }�}�z3á����.: � E�D Ó±�?K Eq:

$¾��Õ#Í � } � & Ô :7��Õ#Í �õ� 25ÍvâOá�ì�:7~qÑ32V8TÍIÏOáqÀ�@ Î ê Î Ö âjÐ�ä3Õ4å±ÖjÑ5Ð Î Ö ÐNXÑyÏS8`XâjÑV�TÍ\�?Ð�ä3Í 20Ñ Î�4� áWÏfØ�ØbØ ì]í?ÜAÚßÞà?��à�l<á�ÿ]Ð�2C: K 6Tá���Ð�:�z3á�� Ì â<å<æ ê }�} � á����.: ê 6 ÓCK ��:

$¶=òå±â Ì ��z�&P�0:Y=�å±â Ì�Î Ö Ð Î á%XA: � æ#Ð � �4Ï�Ð Î á.XA:%¿Õ Î ÖjÍvâvá�À � æ#Íõ@�åvåOÍIÏ Ï � Ñ � ÍP� � Ö æ  á%ê õ � ��ÍIÏ$Í Ì âöåµæ��Í �4Ð�â ÖZá�� Ô ê E ê }n6Tá%=TÍ �#ÖjÍ � ;4Ívâ ê }���zR:

$¶= Ô =RêS}�z�&HÀ)= �&Ì 232 Ô Ð � �*Õ#Ö Ívâ0= � Ï�ÖjÍ � ê Î Ö ÍZâ�é Ì åOÍ Ó�K� áÞ@(�o=Rê7)0z � }R: K á.Xâ Ì é|Ö0��Í �3Ñ�Ï�Ñ0Ð Î ê E�8 á.� Ì âöåµæê }�}�zR:

Page 221: Aggressive Centralized and Distributed Scheduling ofDisk Requests

K E��

$¶=ïÍ Ì�4 } K &T=TÍ Ì'4TÌ ÖjÍ � ÍIåµæ Î Ð�20Ð 4�� áaê Î å�:0á�À)= Ô =Rê0ê Î ÖjÍvâ�é Ì å±Í`=?�4ÍIå±Ñ�  å Ì Ö Ñ5Ð Î áb= �&Ì 232 Ô Ð � �*Õ#Ö Ívâ_= � Ï�ÖjÍ �ê Î ÖjÍvâ�é Ì å±ÍlI9= Ô =Rê�L<á[×a25Ñ0Ö Í ç�âjÐ�ä3Õ4å±ÖG Ì�� Ñ32 �5 á[XÐ�åOÕ � Í Î Ö`��Õ � ;4Ívâõc � 6 K ê 6'E K á_��Í ��ÑyÏ$Ñ5Ð Î Xuá� Ì âöåµæ ê }�} K :

$¶=ïÍ Ì�4 } K�Ì &F=TÍ Ì�4TÌ Ö Í � ÍÃåµæ Î Ð�25Ð 4�� á ê Î å�:0áwÀ�=TÍ Ì'4TÌ Ö Í ç�âjÐ�ä3Õ4å±ÖJ=?�4ÍIåOÑ�  å Ì Ö Ñ0Ð Î á*= �1� ê c�E�E�� Ì�Î ä= �1� ê c�E ê �,×a25Ñ0Ö Í\XÑyÏjåUXâjÑV�TÍTáR= Ô =Rêaê Î Ö Ívâ$é Ì å±Í  á?XÐ�å±Õ � Í Î Ö��Õ � ;4Ívâac ��� E�z ê E�z#áÞ��Í#�3Ñ�Ï�Ñ5Ð Î íuá� å±Ö Ð�;4Ívâ ê }�} K :

$¶=ïÍ Ì�4 }�z�&T=TÍ Ì'4TÌ ÖjÍ � ÍIåµæ Î Ð�20Ð 4�� áYê Î å�:5á[À�=TÍ Ì�4TÌ Ö Í&ç�âjÐ�ä3Õ4å±ÖT=?�4ÍIå±Ñ� �å Ì ÖjÑ5Ð Î áb= � êªê 6'D�En� ê �o���(X Ì�Î ä= � ê K D�D�En� ê �o���(X õ�Ì â â Ì å±Õ4ä Ì XÑ�Ï å1X�â ÑV�TÍïá�= Ô =Rê.ê Î ÖjÍvâ�é Ì å±Í  á�XÐ�åOÕ � Í Î Ö.�Õ � ;4Ívâác ��� E�z?6'E�E�á��Í �3Ñ�Ï�Ñ0Ð Î @øá�ì ÌIÎ Õ Ì â � ê }�}�zR:

$¶=ïÍ Ì�� c�c�&Yç%:W=TÍ Ì��&ÌIÎ áR�o: ð Ñ Î ä�á � :?~qÑV2yÏ$Ð Î À�@ Î @ Î Ì 2 � Ï�Ñ�Ï�ÐIéi@Õ���ÑV25Ñ Ì â �3Ó =TÖ Ðªâ Ì'4 Í0@�åOÖ ÑV��Ñ5Ö �5 á?Ï�Õ>òÝÞÒ É)��à)Üwþ*í?à3l)Ç���Ð�á�ÿ]Ð�2�:�D�á��Ð�:�z�á ê }�c�c3áÞ���.: ê D�� Ó ê 6�E7:

$¶=ïÍ 25Ö�}�E�&P�^:7=ïÍ 25Öf÷vÍvâváïçY: Ô æ#Í Î áRì�: � Õ4Ï�ÖjÍvâ æ*Ð�Õ#ÖZáYÀ�X�ÑyÏ98`=òåµæ#ÍÃä3Õ�25Ñ Î�4 ��Í ��ÑyÏ�Ñ0Ö ÍIä  á�Ã~l í'ıà<àfÅ?Æ�Ç�È�É�í9Ê��ÌË4à�<Æ�ÇR��à�l�6öÝ5Øbó�ÏSäîì]í?ÇZÊIà�l<à)Ç�ıà<á�~ Ì Ï�æ#Ñ Î�4 ÖjÐ Î áÞXA: Ô :5á�ì ÌIÎ Õ Ì â � ê }�}�E�áW�5�.:�z ê z Ó z K�� :

$¶=ïÕ 4�4 }�E�&NXA:Y=TÕ 4�4 ÏOáUÀ � æ#ÍTë�Ï�ÍVÐIéMG Õ*Ö Õ#âjÍTâ Î Ð�Á[20ÍIä 4 ÍVÑ Î Ö æ*ÍTXÍIÏ�Ñ 4�Î ÐIé Ì XÑ�Ï98O=�åµæ*ÍIä3Õ�20Ñ Î�4 @�2 Ó4 Ъâ Ñ0Ö æ �H á�� Ì Ï�Ö ÍZâ � Ï � æ*ÍIÏ�Ñ�ϱá Ô 25Í � Ï�Ð Î ë Î Ñ3�TÍvâ<Ï$Ñ5Ö � á7=TЪÕ#Ö æ ÔAÌ âjÐ�25Ñ Î4Ì á ê }�}�ER:

$¶=ïÕ 4�4 }�z�&NXA:a=TÕ 4�4 ϱá(À�XÑyÏS8ü=ïÕ�;4Ï � Ï�ÖjÍ � çQÍvâ$é|Ð�â �&Ì�Î åOÍ Ì�Î ä^��Í#25Ñ Ì ;#ÑV20Ñ5Ö � × Î æ Ì�Î å±Í � Í Î Ö<Ï � æ#â ÐªÕ 4 æÖ æ*ÍAëóÏ�Í�ÐIé ÔAÌ â Î Ñ3� Ì 2%�?Ñ5âjâ Ð�âöÏ Â á#ç�æ.:jXP: � æ#ÍIÏ�Ñ�ϱá Ô 25Í � Ï$Ð Î ë Î ÑV�TÍvâöÏ�Ñ0Ö � á7=TÐ�Õ*Ö æ ÔAÌ âjÐ�25Ñ Î4Ì á ê }�}�z7:

$ � ÍvЪâ�6 K & � : � ÍvÐ�âjÍ � á � :�ç�Ñ Î 8TÍvâ ÖjÐ Î á�À�@ Ô Ð � � Ì â Ì ÖjÑV�TÍõ@ Î4Ì 2 � Ï�ÑyÏYÐ�é\XÑ�Ï98l=�å<æ#ÍIä3Õ�20Ñ Î�4 çQÐ�20Ñyå±Ñ0ÍIÏ Â áì]í?Ü_Ü_àRÇ�Æ�Ä�����Æyí?Ç?ÉVí9ÊÖ�ÌË4à(ãuìYò á7ÿ]Ð�2C: ê D3á���Ð�:�z3á�� Ì â<å<æ ê }n6 K á����.: ê 6�6 Ó ê � � :

$ ~qÑ325æq6�c�&P�A:?~qÑV20æ#Í 2 � áWÀ�@ Î @ Î Ð �&Ì 2 � Ñ Î XÑ�Ï98H=�åµæ*ÍIä3Õ�20Ñ Î�4 ãY@ Ô Ð � � Ì â Ñ�Ï�Ð Î Ð�éiG Ô Gb= Ì�Î ä=5= � G=TÍvÍ#8<=�å<æ#ÍIä3Õ�20Ñ Î�4 ë�Ï�Ñ Î�4�Ì�Î × � �#Ñ0â Ñ�å Ì 2Þ�?Ð�ä3Í 2�é|Ъâ(X�ÑyÏ98p@�åvå±ÍIÏjÏ�ÍIÏ Â á�ì]í?Ü_Ü_à7Ç�Æ�Ä����CÆyí?ÇnÉuí9ÊÖ�ÌË4àãuìYò�á�ÿ]Ð�2�: ê }3á��Ð5: ê á�ì ÌIÎ Õ Ì â � ê }?6'c�áW���á: ê z Ó ê 6�:

$ ~úÐ�âjÖ�} � & õ :%~ Ъâ Öjæ#Ñ Î�4 Ö Ð Î á(íA:1í ÌIÎ�4 ÍvâZá8�_:]ç Ì ÖjÖvá0À�=�å<æ#ÍIä�Õ�25Ñ Î�4 @U2 4 Ð�âjÑ5Ö æ � Ï÷é|Ъâ`�?Ð�ä3ÍZâ Î X�ÑyÏ98XâjÑV�TÍIÏ Â á�Ã~l í'ıà<àfÅ?Æ�Ç�È�Éóí9Ê\�ÌË4àPÍ�ø?ø îpãuìYòúÝ�Ï'û1òQØAÛqÙ�ÏIìYÝ~ì]í?ÇZÊIà�lµàZÇ�ıàYí?Ç`òùàf��É#àNlµà)Ü[à)ÇR���?Ç�Åòúí'Å3à�жÆ�Ç�È&í9Ê×ì]í?ÜUßÞàn�$à�lUÝÞÒ�É)�$à)ÜoÉOá�� Ì Ï�æR�3Ñ32V20ÍTá � Í Î*Î ÍIÏ Ï$ÍvÍTá5� Ì�� ê }�} � á����.: K'� ê ÓCK D ê :

$ ~úÐ�âjÖ�} �TÌ & õ :.~ Ъâ Ö æ*Ñ Î�4 Ö Ð Î á1íA:�í Ì�Î�4 Ívâvá�_:�ç Ì ÖjÖvá(À�=òåµæ#ÍÃä3Õ�25Ñ Î�4 é|Ð�âN�?Ð�ä3Ívâ Î XÑyÏS8^XâjÑV�TÍIÏ Ì�Î ä�Ð Î#Ó � Ì�Î ä3Ð � ~úÐ�âf8720Ð Ì ä#Ï Â á�ë Î ÑV�TÍZâ<Ï�Ñ0Ö � ÐIé��?Ñ�åµæ#Ñ 4TÌIÎ á � ÍIå<æ Î Ñ�å Ì 2ý��Í �4Ъâ Ö Ô =n× ÓC� � Ó ê } ��Ó } � á� Ì âöåµæ ê }�} � :

$ ~úÐ�âjÖ�}�D�& õ :?~úÐ�âjÖ æ#Ñ Î�4 ÖjÐ Î áqíP:Wí ÌIÎ�4 ÍvâZá��_:#ç Ì Ö ÖZá�ì�:R~qÑV2V8TÍÃϱá.À � Î#Ó 25Ñ Î Í0×�3Öjâ Ì å±Ö Ñ0Ð Î ÐIé1= Ô =nêbX�ÑyÏ98XâjÑV�TÍ&ç Ì â Ì'� ÍvÖ ÍZâ<Ï Â á1Ã~l í'ıà<àfÅ?Æ�Ç�È�É í9ÊH��Ë4à<Í�ø?ø?Î<ãuìYò Ý�Ï�û1ò<ØPÛqÙUÏÃìYÝ|þ#í?Æ�Ç7�(ÏZÇ7��àtl�Ç����CÆyí?Ç���Ðì]í?ÇZÊIà�l<à)Ç�ıà�í?Ç_òùàf��É#àNlµà)Ü[à)ÇR�%�?Ç�ÅÖò~í�Å3à�ÐeÆ�Ç�ÈVí9Ê÷ì]í?ÜUßÞàn�$à�lbÝÞÒ É)��à)ÜoÉOá � ÖjÖ Ì Á Ì á � Î Ö Ì â Ñ0Ð#á?� Ì �ê }�}�D�áq���.: ê � c Ó ê D�c7: