Digital Archaeology: “putting the bits and pieces together from … · Digital Archaeology: “putting the bits and pieces together from damaged magnetic tapes” VIVEK NAVALE NATIONAL

Digital Archaeology: “putting the bits and pieces together from damaged magnetic tapes”

VIVEK NAVALENATIONAL ARCHIVES AND RECORDS ADMINISTRATION

8601 ADELPHI ROAD,COLLEGE PARK, MD, 20740Phone: +1-301-837-3404 FAX: +1-301-837-3681

E-mail: [email protected]

Presented at the THIC Meeting at the Raytheon ITS Auditorium, 1616 McCormick Dr

Upper Marlboro MD 20774-5301October 26-27, 2004

Motivation for the Talk

• What factors effect the stability of magnetic tapes?

• What causes “Stiction” in magnetic tapes?

• How were NARA nine track open reel problem tapes migrated to stable media?

• How to recover electronic records from tapes in adverse situation, in a disaster?

V.Navale, NARA, 2004

Magnetic tape composition and stability

• Magnetic layer – Metal particles, oxides• Substrate layer – polyethylene terephthalate• Binders – Polyester urethanes• Backing Layer – carbon particles dispersed

with binder• All these components are potential sources of

failure for a magnetic tape medium.


AFM image of magnetic recording media


TEM photograph of magnetic tape structure


What parameters effect stability of Magnetic Tapes?

• Environment – temperature, humidity

• Magnetic head – structure and contact area

• Tape composition – abrasive lubricants, magnetic powders, surface roughness, finishing

• System issues – tape tension, magnetic head protrusion, running time, multiple passes, internal temperature

• Dust and PollutantsV.Navale, NARA, 2004

Oxidation can reduce electronic signal


Experimental data showing the effect of humidity on life expectancy of magnetic tapes


Experimental data showing effect of temperature on life expectancy of magnetic tapes


Why do Magnetic Tapes Exhibit Stiction?

• In contact with water, Polyurethane binder undergoes hydrolysis, higher temperatures accelerate the reaction

• Lower molecular weight polymers formed, cause the tape coatings to be become sticky

• Polyurethane hydrolysis can be temporarily partially reversed by heating a tape at a relatively low temperature for several days.


Problems observed with MIRA-1000 type magnetic tapes

• Severe stiction causing frequent tape drive faults.

• Material deposits on a drive head and/or tape cleaner, sometimes removable.

• Holes occurred in the tapes because of coating pullout.

• Stretched and wrinkled tape resulting from the tape having stuck previously in a tape drive.


Effect of Stiction in magnetic tapes


Severe Stiction effect, tapes peeled from Magnetic Heads


Associated Problems with Sticky tapes

- Contamination from Binder decomposition.- Transfer of deposits from tape drive to the tape

surfaces- De-lamination of magnetic coating if the tape is

forcefully unwound.

- Widespread layer-to-layer adhesion with gross de-lamination of the magnetic coating as the tape is unwound. Stretching or tearing of tapes occur when tapes are stuck in the drive.


Tape de-lamination resulting from stick tapes


Recovering electronic records from sticky tapes• Operate tape drive at the slowest possible speed;

minimize heat buildup in the tape path.

• Clean the entire tape path before processing each tape.Remove any and all sticky residue from previously processed tapes.

• Do not use a tape cleaner to clean sticky tapes. Cleaning blades can “open” the tape surface resulting in more rapid buildup of tape debris in a drive’s tape path.


Heat is not “Cure All” procedure

• Store the tapes at low relative humidity (35-40%) and at a temperature in the range of 66-68 F.

• Heating a tape that has become sticky for reasons other than hydrolysis can destroy the tape and make recovery of the data impossible.

• Next photograph shows what can happen by heating sticky tapes not caused by hydrolysis.


Effect of Heat damage on Magnetic Tapes

V. Navale, NARA, 2004

How to recover data from damaged tapes?

- Try multiple tape passes

- Read block-by block & record to new mediaDevelop software routine to accounts for blocks read, accountfor missing blocks. Report on the exact number of blocks copied after the end of file or end of volume.

- Gather block fragments and “piece together” all blocks. Write “dummy blocks” to output if needed.

- Data recovery success average 98%


Block #20 needs to be recovered from the backup


Original Data for Block# 20-23

START

Make repairs: smoothing wrinkles and hand cleaning tape

SCAN for duplicate blocks for each recovered file on hard disk. If there are dup. blocks, then delete them.

All Recovered ?

MERGE: The needed segments are identified and merged together.

Secondary Tape ?

Primary?

Read Problems?

WRITE block to file on hard disk

EOT ?

Recover only missing blocks from PrimaryN

N

N

Y

N N

Y

END

Y

Y

Y

NARA, Data Recovery plan

READ block of data

Need to recover Secondary tape



START

Verifying data recovered on 3480 cartridges with APS’ TapeMap or

Dump

N

Y

Data Readable ?

Verifying data recovery process by analyzing eMag’s reports

Inform the errors to eMagand ask for investigating the

problem

END

Verification of Data Recovered (data recovered on 3480 cartridges)

Phase 1

Phase 2

START

Run APS’ TapeMap on 3480 cartridge containing data recovered

by eMag Solutions

N

Y

Data Readable ?

Get result from TapeMap, then check with CDB or old folder to make sure all file

meta data is correct.

Inform the errors to eMagand ask for investigating the

problem

END

Phase 1

Everything OK ?

Y

N


START

Get Block Count (from label) for the file and enter it into F6

Read a Line ( ignore label )

KW=RE KW=SR KW=TSKW=SFKW=BC

F1 = BC(value)Update F4 and F7

F3 = YESUpdate F5

F2= +SF(value)Update F5

F2= -SR(value)Update F3,F1,F4,F5

EXIT(abort)

EOV / EOF

Dup.Blocks in Report #3 ?

Update F8 (value from Report #3)

Adjust values related to file segment containing dup.blocks, then adjust others values in trace table

#BC + #RE = BlockCount ?

Identify Unrecoverable Blocks

Report the problem to eMag and ask for redo the job or more

explanations on problem encountered

N

Y

N

Y

N

Phase 2

END

N N N N

Y Y Y Y Y

Key Word = KWBlock Copied = BC

Read Error = RESpace Forward = SFSpace Reverse = SR

Tape Stuck = TSEnd of File = EOF

End of Volume = EOV

Y


How to minimize Data loss?

• Use certified media to archive electronic information.

• Allow for incoming media to acclimatize for a minimum of 24 hours before attempting to process.

• Archive tapes in controlled environment. Temp 66-68 F and 30-35% humidity.

• Rewind/retension all media types.• Migrate E-records from legacy media formats to

newer formats.


Acknowledgement

NARA Data Recovery TeamHoang Nguyen, Ross Cameron and Nadi Mirvahabi

NARA contract to e-Mag Solutions - NAMA-02-D-007

eMag Solutions Team, LLCBill King, Marvin Howell, Brendan Sullivan


Documents

Digital Archaeology: “putting the bits and pieces together from … · Digital Archaeology: “putting the bits and pieces together from damaged magnetic tapes” VIVEK NAVALE NATIONAL