Data Recovery of Magnetic Tape

Digital Archaeology: “putting the bits and pieces
together from damaged magnetic tapes”
VIVEK NAVALE
NATIONAL ARCHIVES AND RECORDS ADMINISTRATION
8601 ADELPHI ROAD,COLLEGE PARK, MD, 20740
Phone: +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 20774-5301
October 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.
V.Navale, NARA, 2004
AFM image of magnetic recording media
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TEM photograph of magnetic tape structure
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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 Pollutants
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Oxidation can reduce electronic signal
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Experimental data showing the effect of humidity on
life expectancy of magnetic tapes
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Experimental data showing effect of temperature on
life expectancy of magnetic tapes
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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.
V.Navale, NARA, 2004
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.
V.Navale, NARA, 2004
Effect of Stiction in magnetic tapes
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Severe Stiction effect, tapes peeled from Magnetic Heads
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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 delamination of the magnetic coating as the tape is
unwound. Stretching or tearing of tapes occur when
tapes are stuck in the drive.
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Tape de-lamination resulting from stick tapes
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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.
V.Navale, NARA, 2004
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.
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Effect of Heat damage on Magnetic Tapes
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How to recover data from damaged tapes?
- Try multiple tape passes
- Read block-by block & record to new media
Develop software routine to accounts for blocks read, account
for 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%
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Block #20 needs
to be recovered
from the backup
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Original Data for Block# 20-23
NARA, Data Recovery plan
START
N
Primary?
Recover only missing
blocks from Primary
Y
READ block of data
N
Read
Problems?
Y
Make repairs: smoothing wrinkles
and hand cleaning tape
WRITE block to
file on hard disk
Need to recover
Secondary tape
N
EOT ?
Y
SCAN for duplicate blocks for each recovered file on
hard disk. If there are dup. blocks, then delete them.
N
All Recovered ?
Y
N
Secondary
Tape ?
Y
MERGE: The needed segments are
identified and merged together.
END
V.Navale, NARA, 2004
Verification of Data Recovered
(data recovered on 3480 cartridges)
START
Phase 1
Verifying data recovered on 3480
cartridges with APS’ TapeMap or
Dump
N
Data Readable ?
Inform the errors to eMag
and ask for investigating the
problem
Y
Phase 2
Verifying data recovery process by
analyzing eMag’s reports
END
V. Navale, NARA, 2004
START
Phase 1
Run APS’ TapeMap on 3480
cartridge containing data recovered
by eMag Solutions
N
Data Readable ?
Y
Get result from TapeMap,
then check with CDB or old
folder to make sure all file
meta data is correct.
N
Everything OK ?
Inform the errors to eMag
and ask for investigating the
problem
Y
END
V.Navale, NARA, 2004
START
Phase 2
Key Word = KW
Block Copied = BC
Read Error = RE
Space Forward = SF
Space Reverse = SR
Tape Stuck = TS
End of File = EOF
End of Volume = EOV
Get Block Count (from label) for
the file and enter it into F6
Read a Line ( ignore label )
N
N
KW=BC
N
KW=RE
Y
Y
F1 = BC(value)
Update F4 and F7
N
KW=SF
KW=SR
Y
F3 = YES
Update F5
KW=TS
Y
F2= +SF(value)
Update F5
Y
F2= -SR(value)
Update F3,F1,F4,F5
EXIT
(abort)
EOV / EOF
N
Y
Update F8 (value from Report #3)
N
Dup.Blocks in Report #3 ?
Y
Adjust values related to file segment containing dup.blocks, then adjust others values in trace table
N
#BC + #RE = BlockCount ?
Y
Report the problem to eMag and
ask for redo the job or more
explanations on problem
encountered
Identify Unrecoverable Blocks
END
V.Navale, NARA, 2004
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.
V.Navale, NARA, 2004
Acknowledgement
NARA Data Recovery Team
Hoang Nguyen, Ross Cameron and Nadi Mirvahabi
NARA contract to e-Mag Solutions - NAMA-02-D-007
eMag Solutions Team, LLC
Bill King, Marvin Howell, Brendan Sullivan
V.Navale, NARA, 2004