Embed Size (px)
Citation preview
Buffer-to-Buffer Credits, Exchanges, and Urban Legends
Lou Ricci, EMCHoward L. Johnson, Brocade
14 August 2013 (8:00am – 9:00am)Session 14281
QR Code
Legal Stuff
• Notice• IBM may have patents or pending patent applications covering subject matter
described in this document. The furnishing of this document does not give you any license to these patents. You can send license inquiries, in writing to: IBM Director of Licensing, IBM Corporation, North Castle Drive, Armonk, NY 10504-1785 U.S.A.
• Any references in this information to non-IBM Web sites are provied for convenience only and do not in any manner serve as an endorsement of those Web sites. The materials at those Web sites are not part of the materials for this IBM product and use of those Web sites is at your own risk.
• Trademarks• The following terms are trademarks of the International Business Machines
Corporation in the United States, other countries, or both: FICON® IBM® RedbooksTM System z10TM z/OS® zSeries® z10TM
• Other Company, product, or service names may be trademarks or service marks of others.
Abstract
• Performance in a FICON network is influenced by the underlying flow control mechanisms of Fibre Channel. In this session, we examine how Buffer-to-Buffer credits flow from the channel to the control unit. We also look at how exchanges are used in FICON applications and how they change with the introduction of zHPF. During both examinations, we explore the role of the FICON Director in managing Buffer-to-Buffer credits and exchanges over a cascaded network. Throughout the session, we debunk the various FICON “Urban Legends” featuring credits and exchanges. Take the opportunity to learn from two of the FICON industry’s leading experts in channel and fabric development and join our session.
Agenda
• Buffer Credits• What are they and how do they work?
• How do you fill the pipe?• What if you can’t fill the pipe?• What’s wrong with multiple senders and one receiver?• What happens when the pipes are different sizes?• What’s it like in the real world?
• Exchanges• What are they and how do they work?
• What’s an Exchange?• How many exchanges are needed?• Can they be "reused?”• Can you have too many exchanges?
BUFFER CREDITSWhat are they and how do they work?
What is Buffer-to-Buffer Credit?
• The greater the BB Credit….• A. The faster frames can be sent• B. The farther apart the two ports can be• C. The larger the frames can be• D. None of the above
What is Buffer-to-Buffer Credit?
• The greater the BB Credit….• A.• B. The farther apart the two ports can be• C.• D.
Flow Control
• Related to the devices’ ability to receive and process frames• Manages when frames are coming faster than they can be processed• Dropped frames occur when frames are arriving too fast to be processed
• Frames can only be transmitted when the receiver is ready• Credit establishment communicates the number of frames a device can receive at a time• The credit value is exchanged at login• Transmission stops when credit runs out• The receiver indicates when it is ready to receive more frames
Credit exchange at Fabric Login
Host says, “I can receive 40 frames.”
Switch says, “I can receive 8 frames.”
Storage says, “I can receive 16 frames.”
Buffer Credit
• At initialization, the two ports establish credit• Each buffer credit corresponds to a frame (regardless of size)
• Each side can support different values• Credit Count
• If a port doesn’t have credit, it can’t send a frame• Credit Count has reached zero
• Mechanism limits frame drops
Credit accounting after Fabric Login
Host thinks, “Good, I can send 8 frames without thinking about it.”
Storage thinks, “Good, I can send 8 frames without thinking about it.”
Switch thinks, “OK, I can send 40 frames that way and 16 frames this way, but I have to think about it.”
Credit Count8
Credit Count8
Credit Count40
Credit Count16
Receiver Ready (R_RDY)
• R_RDY• Used for link level flow control• Called buffer-to-buffer credit (BB
Credit)• R_RDY is not a frame
• It is a “primitive” so it doesn’t consume a buffer
• Frame transmission• BB Credit is decremented
• Once for each frame transmitted• When BB Credit = 0
• Transmission stops• Frame received
• R_RDY is sent• Causes transmitter to increment BB
Credit
Credit Accounting during Transmission
Host says, “I can send 8 frames without stopping.”
Switch says, “I can 40 frames that way and 16 frames the other way without stopping.”
Storage says, “I can send 8 frames without stopping.”
Credit Count1
Credit Count40
Credit Count5
Credit Count16R_RDY
R_RDY
Urban Legend:Buffer Credits at Zero are a Problem
• Buffer credit determines DISTANCE• The distance two nodes can be apart and still maintain full link frame rate
• Buffer credit is the number of FRAME buffers• A port provides for it’s NEAREST neighbor for RECEIVING frames• Does NOT have to be symmetrical
• Buffer credit is a FRAME count• Not a data SIZE• A 1 byte frame consumes 1 buffer credit• A 2K byte frame consumes 1 buffer credit
• Number of credits needed is determined by:• Raw Link Speed• Speed of light thru a fiber• Distance between two adjacent nodes
How Long is a Fibre Channel Frame?
12
BUFFER CREDITSExample: A full pipe
20
Channel “Perfect” Switch Control Unit
Initial Conditions
Number of B-B Credits the switch advertised to the channel during link init
NOTE: In these animations, both the frames and R_RDY’s are numbered. This is for illustrative purposes only. In reality, neither the frames nor the R_RDY’s are numbered. The arrival of an R_RDY only informs the receiver that A frame has been forwarded, not WHICH frame has been forwarded.
20
19
1
18
12
17
3 12
16
3 14 2
15
5 3 14 2
14
5 3 16 4 2
13
7 5 3 16 4 2
12
78 5 3 16 4 2
11
9 78 5 36 4 2 1
1
9 78 5 36 410
10
12
1 2
9
9 78 56 41011 3 12
31 2
8
9 78 56101112 3 14 2
1 2 3 4
7
9 78 610111213 5 3 14 2
1 2 3 4 5
6
9 781011121314 5 3 16 4 2
1 2 3 4 5 6
5
9 8101112131415 7 5 3 16 4 2
1 2 3 4 5 6 7
4
910111213141516 78 5 3 16 4 2
1 2 3 4 5 6 7 8
4
1011121314151617 9 78 5 3 16 4 2
2 3 4 5 6 7 8 9
4
1112131415161718 9 78 5 3 16 4 210
3 4 5 6 7 8 9 10
4
1213141516171819 9 78 5 36 4 21011
4 5 6 7 8 9 1011 1
THIS PAGE INTENTIONALLY LEFT BLANK
BUFFER CREDITSExample: A not so full pipe
20
Suppose the switch is too far away from the channel for the B-B credit it advertised to the channel
19
1
18
12
17
3 12
16
3 14 2
15
5 3 14 2
14
5 3 16 4 2
13
7 5 3 16 4 2
12
78 5 3 16 4 2
11
78 5 3 16 4 29
10
8 6 4 210 7 5 3 19
9
78 5 3 16 4 291011
8
78 5 3 16 4 29101211
7
78 5 3 16 4 2910111213
6
78 5 3 16 4 291011121314
5
78 5 3 16 4 29101112131415
4
78 5 3 16 4 2910111213141516
1
3
78 5 3 16 4 291011121314151617
1 2
2
78 5 3 16 4 29101112131415161718
1 2 3
1
78 5 3 16 4 2910111213141516171819
1 2 3 4
0
78 5 3 16 4 291011121314151617181920
1 2 3 4 5
0
78 5 3 16 4 291011121314151617181920
1 2 3 4 5 6
0
78 5 3 16 4 291011121314151617181920
1 2 3 4 5 6 7
0
78 5 3 16 4 291011121314151617181920
1 2 3 4 5 6 7 8
0
78 5 3 16 4 291011121314151617181920
1 2 3 4 5 6 7 8 9
0
78 5 3 16 4 291011121314151617181920
1 2 3 4 5 6 7 8 9 10
0
78 5 36 4 291011121314151617181920
1 2 3 4 5 6 7 8 9 1011 1
0
78 5 36 491011121314151617181920
1 2 3 4 5 6 7 8 9 101112 1 2
0
78 56 491011121314151617181920
1 2 3 4 5 6 7 8 9 10111213 1 2 3
0
78 5691011121314151617181920
1 2 3 4 5 6 7 8 9 1011121314 1 2 3 4
0
78 691011121314151617181920
1 2 3 4 5 6 7 8 9 101112131415 1 2 3 4 5
0
7891011121314151617181920
2 3 4 5 6 7 8 9 101112
21
13141516 1 2 3 4 5 6
0
891011121314151617181920
3 4 5 6 7 8 9 101112
2122
1314151617 1 2 3 4 5 6 7
0
91011121314151617181920212322
4 5 6 7 8 9 101112131415161718 1 2 3 4 5 6 7 8
0
1011121314151617181920212324 22
5 6 7 8 9 10111213141516171819 1 2 3 4 5 6 7 8 9
0
21
1 2 3 4 5 6 7 8 9 10
2324 2225
6 7 8 9 1011121314151617181920
11121314151617181920
0
21
2 3 4 5 6 7 8 9 10
2324 222526
7 8 9 1011121314151617181920
121314151617181920
11
0
21
3 4 5 6 7 8 9 10
2324 22252627
8 9 1011121314151617181920
1314151617181920
1112
0
21
4 5 6 7 8 9 10
2324 2225262728
9 1011121314151617181920
14151617181920
111213
0
212324 222526272829
1011121314151617181920
151617181920
5 6 7 8 9 10 11121314
0
212324 22252627282930
11121314151617181920
1617181920
6 7 8 9 10 1112131415
0
212324 2225262728293031
121314151617181920
17181920
7 8 9 10 111213141516
0
212324 222526272829303132
1314151617181920
181920
8 9 10 11121314151617
0
212324 22252627282930313233
14151617181920
1920
9 10 1112131415161718
0
212324 2225262728293031323334
151617181920
20
10 111213 151617181914
0
212324 222526272829303132333435
1617181920 11121314151617181920
0
212324 22252627282930313233343536
181920 2117 121314151617181920
0
212324 22252627282930313233343536
181920 13141516171819202122
37
0
212324 22252627282930313233343536
1920 14151617181920212223
3738
0
212324 22252627282930313233343536
20 15161718192021222324
373839
0
212324 22252627282930313233343536
1718192021 25222324
37383940
16
0
212324 22252627282930313233343536
17181920212223242526
37383940
0
212324 22252627282930313233343536
181920222324252627
37383940
21
0
212324 22252627282930313233343536
192022232425262728
37383940
21
0
212324 22252627282930313233343536
202223242526272829
37383940
21
0
212324 22252627282930313233343536
222324252627282930
37383940
21
0
2324 22252627282930313233343536
222324252627282930
37383940
21 31 21
0
2324252627282930313233343536
3132
37383940
22232425262728293021 2221
THIS PAGE INTENTIONALLY LEFT BLANK
BUFFER CREDITSExample: Different sized pipes
Fat Pipe Skinny Pipe
Fat Pipe / Skinny Pipe
20
8 Gig Link 4 Gig Link
Fat Pipe Skinny Pipe
19
1
18
12
17
3 12
16
3 14 2
15
5 3 14 2
14
5 3 16 4 2
13
7 5 3 16 4 2
12
78 5 3 16 4 2
11
9 78 5 36 4 2 1
10
9 78 5 36 410 1
2
1
9
19 78 56 41011
1
2
3
8
12
4
9 78 56101112
1 2
3
7
1239 78 610111213
1 2
45
6
123
456
9 781011121314
1 2 3
5
1234
567
9 8101112131415
1 2 3
4
1234
5678
910111213141516
1 2 3 4
3
12345
56789
1011121314151617
1 2 3 4
3
12345
56789
10
1112131415161718
52 3 4
2
6 12345
7891011
1213141516171819
52 3 4
2
6 2345
789101112
20 13141516171819
5 63 4
1
6 23457
89
10111213
2021 141516171819
53 4 6
1
6 3457
89
1011121314
202122 1516171819
5 74 6
0
6 34578
9101112131415
20212223 16171819
5 74 6
0
6 4578
910111213141516
20212223 171819
5 7 86
24
0
9 6 4578
1011121314151617
20212223 181924
5 7 86
0
9 6 578
101112131415161718
23 20212223 1924
97 86
0
10 9 6 578
1112131415161718
23 20212223
19
24
97 86
0
10 9 678
111213141516171819
2325 21222324
97 8 10
20
0
11 10 9 678
121314151617181920
2325
21
222324
97 8 10
0
11 10 9 78
12131415161718192021
26 2325
22
2324
9 118 10
0
12 11 10 9 78
13141516171819202122
26 2325
23
24
9 118 10
0
12 11 10 9 8
1314151617181920212223
26 2325
24
27
9 11 1210
0
13 12 11 10 9 8
1415161718192021222324
26 232527
9 11 1210
0
13 12 11 10 9
1415161718192021222324
2628 2527
23
1311 1210
0
2628 2527
1311 1210
14 13 12 11 10 9
1516171819202122232423
0
14 13 12 11 10
1516171819202122232423
25 2628
25
27
1311 12 14
THIS PAGE INTENTIONALLY LEFT BLANK
BUFFER CREDITSExample: Real Life?
20
20
More real life example: Two senders sending at 30% - 50% link rate to one receiver
19
19
1
1
18
18
12
12
17
18
3 12
12
16
18
3 14 2
12
16
17
3 14 2
3 12
16
16
3 14 2
3 14 2
16
16
3 14 2
3 14 2
15
16
3 14 2
3 14 2
5
15
16
3 14 2
3 14 2
5
15
16
34 2
34 2
5
1
1
1
15
15
34
34
52
11
2
5
1
1
14
14
112
3
2
2
4
34
5
5
6
6
1
1
14
14
5
5
6
6
1122
34
21
1 2
34
14
14
11223
4
3
4
5
5
6
6
21
1 2
3
14
14
11223
4
4
3
31 2
5
5
6
6
21 3
14
13
1122334
4
4
5
5
6
6
31 2
21 3
7
14
13
11223344
5
4
5
6
67
31 2
421 3
13
13
112233445
5
5
6
67
421 3
431 2
7
14
13
112233445
5
6
67
7
542 3
431 2
13
14
12233445
6
67
7
5
5
8
542 3
432
13
13
223344556
6
6
7
78
543
5432
8
9
12
14
23344556
6543
543
7
78
8
9
6
6
10
13
14
33445566
7
78
8
910
654
543 6
12
15
3445566
7
78
8
91011
654
54 6
13
15
445566
78
8
91011
7
7
65
54 6
13
15
45566
78
8
91011
7
7
65
5 6
9
14
15
5566
8
8
91011
77
7
7
6
5 6
9
13
15
56677
8
8
91011
7
7
6
5 6
9
12
13
16
56677
8
91011
8
87
7
6
6
9
12
14
16
667788
9
8
1011
87
76
9
12
BUFFER CREDITSExample: Cascaded Directors
8208
7
1
820
6
12
820
5
3 12
820
4
3 14 2
820
3 819
1
1
5 34 2
2 818
12
1 2
5 36 4
1 817
31 2
3 127 56 4
0 816
1 2 3 4
3 14 278 56
0 815
2 3 4 5
5 3 14 29 78 6
0 814
5 3 16 4 278910
3 4 5 6
0 813
7 5 3 16 4 2891011
4 5 6 7
0 812
78 5 3 16 4 29101112
5 6 7 8
0 811
9 78 5 3 16 4 210111213
6 7 8 9
0 810
9 78 5 3 16 4 21011121314
7 8 9 10
0 79
12131415
8 9 1011
9 78 5 36 4 21011
1
1
0 68
78 5 36 49101112
1 2
1213141516
9 101112
0 57
14151617
10 111213
3 1278 56 4910111213
1 2 3
0 46
78 5691011121314
1 2 3 4
15161718
11121314
3 14 2
0 35
5 34 278 69101112131415
1 2 3 4 5
16171819
12131415 1
0 24
5 36 478910111213141516
1 2 3 4 5 6
17181920
13141516 1 2
0 13
7 56 4891011121314151617
1 2 3 4 5 6 7
18192021
14151617 1 2 3
0 02
78 569101112131415161718
1 2 3 4 5 6 7 8
19202122
15161718 1 2 3 4
0 01
78 6910111213141516171819
1 2 3 4 5 6 7 8 9
20212322
16171819 2 3 4 5
0 00
78910
1 2 3 4 5 6 7 8 9 10
11121314151617181920212324 22
17181920 3 4 5 6
0 00
891011
2 3 4 5 6 7 8 9 10
121314151617181920
11
212324 2225
181920 21 4 5 6 7
THIS PAGE INTENTIONALLY LEFT BLANK
Slow Drainers• A device that delays the return of BB credit significantly slower than the desired load
• Moderate delays can cause performance impacts even to other uninvolved devices
• Severe delays can cause errors (IFCCs), even to other uninvolved devices
10
10
Slow Drainer
12
10
66
1
10
10
12
9
66
1
12
9
10
12
8
66
12
1
3
12
8
9
12
7
66
12
2 1
3
12
8
8
12
7
66
3 12
2 1
3
12
7
8
12
7
66
3 12
2 13
3
1
2
4
7
7
12
6
56
3
1
2
2 134
4
2 1
3
4
6
6
11
6
46
3
12
2
1
34
4
23
4
5
6
6
5
36
10
3
2
34
4
5
6
5
9
5
36
12 1 3
4
5
3122 1
34
4
5
5
6
4
5
5
4
8
5
46
3 122 1
3
4
4
4
5
5
5
6
6
5
4
7
5
46
3 122 134
4
5
5
5
67
4
6
6
3
6
6
46
3 122
1
3 5
5
5
67
6
6
5
4
5
7
35
4
4
3 22
1
344 5
5
5
67
6
6
8
6
3
4
7
25
3 2
2
1
3445
5
6
7
6
6
8
5
3
3
6
34
7
9
7
3
2
34455 6
7
6
6
8
6
4
2
6
34
7
9
78
Notice NO R_RDY
3
2
34455 6
7
6
8
6
4
2
6
34
7
9
78
3
3
4455 676
8
6
4
2
7
43
7
9
78
8
10
34
455 676
8
6
4
2
7
42
7
9
78
8
10
1
34
455 6768
5
4
2
7
42
7
97
8
8
1011
9
9
1
5768
5
4
1
7
41
7
9
7
8
8
1011
9
9
4
5
6 4
12
1
5768
6
4
1
7
31
79 78
8
1011
9
9
56
12
2
5768
5
5
1
6
21
79 88
10
11
9
9
56
10
12
2
10
5
7
68
6
5
1
6
30
79810
11
9
9
6
10
1213
2
10
7
68
6
5
1
7
31
79810
119
9
10
1213
10
7
6
8
6
5
1
7
30
7981011
11
9
10
12
1314
11
10
9
8
6
4
1
7
30
7981011 99
10
12
1314
11
15
10
11
3
86
5
1
7
20
79
81011 910 12
13
14
11
15
10
11
3
12
This frame is blocked:Head of Line Blocking!
7
4
1
7
30
10
11 910 1213
14
11
1516
11
3
9
8
12
10
6
5
1
7
40
9
8
1011
9
10 121314
11
15
12
16
11
13
12
6
5
1
7
40
10
11
9
10 12131411
15
12
1617
11
4
13
12
8
6
5
1
7
40
1013141115
12
1617
11
4
13
13
12
810
11
9
12
6
5
0
6
40
1314111512
16
1718
11
4
10
1314
13
12
14
10
11
9
12
6
5
0
6
40
14111512
16
13
1718
10
5
14
13
12
14
10
11
9
12
13
6
5
0
6
40
14
111512 1613
17
18
14
5
19
12
11
10
13
1314
12
9
10
6
4
0
7
40
14
11
1512 1617
18
5
19
12
11
10
13
131415
20
12
1314
10
9
6
5
0
7
30
14
11
15
12 1617
18
19
12
11
10
13
131415
20
1213
14
5
5
0
6
20
14
11
15
12
16
17
18
19
12
11
10
13
13
1415
20
1314
21
6
16
15
5
5
0
7
30
14
11
15
12
16
17
18
19
12
11
10
13
1314
15
20
14
21
6
16
15
5
5
0
7
40
14
11
15
12
16
1718
19
12
10
13
1314
15
2021
6
16
15
22
17
5
5
0
8
50
1411
15
12
16
17
18
19
12
10
13
1314
15
2021
16
15
22
17
5
4
0
9
50
14
11
15
12
16
17
1819
12
10131314
15
20
21
16
15
22
17
23
4
4
0
9
40
14
11
15
12
16
17
1819
12
10131314
15
20
21
16
15
22
17
23
7
18
5
4
0
9
40
14
11
15
12
16
17
1819 13
13
14
15
20
21
16
15
22
17
23
7
18
5
4
0
9
40
14
11
15
12
16
17
18
19 13
13
14
15
20
21
16
22
17
23
7
18
24
What Can Be Done About A Slow Drainer?
• Difficult to identify the culprit– Sometimes issues are intermittent– There may be more than one gremlin
• Tools are available to help!– “Bottleneck Detection”
See Also:https://elabnavigator.emc.com/vault/pdf/FC_SAN.pdfhttps://www.ibm.com/developerworks/mydeveloperworks/blogs/sanblog/entry/how_to_deal_with_slow_drain_devices20?lang=enhttp://www.brocade.com/downloads/documents/html_product_manuals/NA_SAN_1130/wwhelp/wwhimpl/common/html/wwhelp.htm#href=Ch_Performance.31.7.html&single=true
What Can Be Done About A Slow Drainer?
• Creates an alert when a port(s) have zero credit for a user selectable amount of time
• Use detection mechanisms to monitor ISLs portsand F_Ports
SAN Performance Gotcha’s
• Oversubscription• Trying to send more than can be received
• Slow draining• Unable to receive what is being sent in a timely manner
245
Culprits
• Oversubscription• Big pipe to small pipe
• Signal degradation• Failing SFP• Poor connections• Insufficient cable hygiene
• Unexpected slow down• Big pipe to small pipe (16G to 2G)• Narrow bridge (reduced ISL bandwidth)
• Odd stuff• Long links• Zoning conflicts• Invalid Attachment / Decommissioned Channel/CU Port• Queue depth
246
Stuff to Look For
• Physical Errors• Detected (Obvious stuff)
• Logins & Logouts• Link Failures
• Undetected (Not Obvious)• CRC Errors
• Encoding errors (inside of a frame)
• Code Violation Errors• Loss of synchronization• Loss of signal
• Loss of Sync• Encoding errors (outside
of a frame)
• Logical Errors• Credit Starvation
• Time at zero credit• Link Resets• Class 3 Discards
• Response Times• High CMR• Exchange Completion
Times • SCSI Reservation Conflicts
247
BUFFER CREDITSOther Neat Stuff
How Does Credit Affect Throughput?
4 20 36 52 68 84 100 116 132 148Distance (Km)
102030405060708090
100110
Per
cent
Dat
a R
ate
4Gb32 Credits
• Absolute Minimum Formula:
Number of credits needed = 1 + Link speed in Gb/s * Distance in KmAverage Frame Size in KB
How Much Credit Do I Need For A Given Distance?
This “1” is to account for the processing delay in a real device
This accounts for round trip time on the fiber
This is the HARD part
Average Ficon Frame Size vs Block Size
Average Frame Size for 28K I/O
600.00
800.00
1000.00
1200.00
1400.00
1600.00
1800.00
2000.00
1 2 3 4 5 6 7 8 9 10 11 12
28K X N
Series1
Average Frame Size for 4K I/O
600.00
800.00
1000.00
1200.00
1400.00
1600.00
1800.00
2000.00
1 2 3 4 5 6 7 8 9 10 11 12
4K X N
Ave
rage
Fram
eSi
ze
Number of records per I/O Number of records per I/O
How Should I Configure My BB Credit?
Local links under 1Km in length:– Even at 8G and small frame size, < 16 credits required
1 + ((8*1) / .8) = 11
Provision ISLs with extra headroom– Use formula, and round UP
1 + ((8*10) / 1.5) = 54
EXCHANGES
Urban Legend:FICON uses fewer Exchanges Than FCP
• In Ficon, each concurrent I/O operation uses two Exchanges• One unidirectional Exchange for IUs from the Channel to the CU• A different unidirectional Exchange for IUs from the CU to the
Channel
• The PAIR is commonly know as a “Ficon Exchange”
How many Exchanges do I need?
• Little’s Law states:• The number of “things” in a system can be determined by multiplying the
average arrival rate of those “things” by the average time each “thing” stays in the system.
• Applied to Ficon:• The average number of Exchanges active at any given time =
Average I/O rate * Average response time
• Example: 5000 Ficon I/Os / Second on a given channel with .4ms service time1 needs 2 Active Exchanges (pairs) at any given time
1 The amount of time the I/O is active in the channel
Urban Legend:Ficon is More Sensitive to Errors than FCP
• Is a Ficon frame more likely to get lost, damaged or corrupted than FCP?• No, the probability is the same
• When a Ficon frame gets lost, damaged or corrupted, is the recovery action different from FCP?• Not really. They are both retried, FCP by the Device Driver,
Ficon by IOS/ERP
So What are the Differences?
• z Operating Systems tend to provide more detailed messages
• Ficon does provide additional debug data and actions• RNID• Link Error Status Blocks• Extensive State Change Processing
Source: FC-FS-3 INCITS/T11 Draft Standard v0.92
See www.t11.org
Summary
• Buffer Credits• Distance• Flow Control
• Exchanges• Unidirectional• Bidirectional
Wednesday August 14, 2013 -- 11:00pm to 12:00pm -- Session 14482
……Newly Scheduled Presentation……
Brocade SAN and FICON UpdatePlease consider attending to discover the innovation
of Brocade’s Gen 5 Fibre Channel Architecture
259© 2012-2013 Brocade - For Boston Summer SHARE 2013 Attendees
THANK YOU!
SHARE, Boston, August 2013Buffer-to-Buffer Credits, Exchanges, and Urban LegendsSession 14281
QR Code
REFERENCES
Speaker Biography
• Lou Ricci• EMC
• 1 Year• IBM
• 34-years• 24-years in channel development• An inventor of FICON• FICON Firmware Team Leader
• Contact Information• [email protected]
Speaker Biography
• Howard L. Johnson• BROCADE• Technology Architect, FICON
• 29 years technical development and management
• Contact Information• [email protected]
BONUS SLIDES
End to End Credit
• Device to Device Flow Control• Between source and destination
• Not the links• Similar to buffer-to-buffer flow control
• At N_Port Login• Report available receive buffers (EE_Credit)• Transmitter counts buffers transmitted (EE_Credit_CNT)• Receiver acknowledges frame (ACK)
• ACK 1 (a single data frame in a sequence) – most common• ACK n (several (N) consecutive data frames in a sequence)• ACK 0 (all data frames in a sequence) – not used
Virtual Channels
• Technology to allocate BB_Credits to particular data flows• Class F traffic has one data flow• Assigned with Zoning by using special Zone names
