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

Transcription

1 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, Phone: FAX: Presented at the THIC Meeting at the Raytheon ITS Auditorium, 1616 McCormick Dr Upper Marlboro MD October 26-27, 2004

2 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?

3 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.

4 AFM image of magnetic recording media

5 TEM photograph of magnetic tape structure

6 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

7 Oxidation can reduce electronic signal

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

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

10 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.

11 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.

12 Effect of Stiction in magnetic tapes

13 Severe Stiction effect, tapes peeled from Magnetic Heads

14 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.

15 Tape de-lamination resulting from stick tapes

16 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.

17 Heat is not Cure All procedure Store the tapes at low relative humidity (35-40%) and at a temperature in the range of 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.

18 Effect of Heat damage on Magnetic Tapes V. Navale, NARA, 2004

19 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%

20 Block #20 needs to be recovered from the backup V. Navale, NARA, 2004

21 Original Data for Block# 20-23

22 START NARA, Data Recovery plan Primary? N Recover only missing blocks from Primary Y READ block of data Read Problems? N Y Make repairs: smoothing wrinkles and hand cleaning tape WRITE block to file on hard disk Need to recover Secondary tape N EOT? SCAN for duplicate blocks for each recovered file on hard disk. If there are dup. blocks, then delete them. Y All Recovered? N Secondary Tape? N Y Y MERGE: The needed segments are identified and merged together. END

23 Verification of Data Recovered (data recovered on 3480 cartridges) START Phase 1 Verifying data recovered on 3480 cartridges with APS TapeMap or Dump Data Readable? Y N Inform the errors to emag and ask for investigating the problem Phase 2 Verifying data recovery process by analyzing emag s reports END V. Navale, NARA, 2004

24 Phase 1 START Run APS TapeMap on 3480 cartridge containing data recovered by emag Solutions Data Readable? N Y Get result from TapeMap, then check with CDB or old folder to make sure all file meta data is correct. Everything OK? N Inform the errors to emag and ask for investigating the problem Y END

25 Phase 2 KW=BC START Get Block Count (from label) for the file and enter it into F6 Read a Line ( ignore label ) N N N N KW=RE KW=SF KW=SR KW=TS 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 Y Y Y Y Y F1 = BC(value) Update F4 and F7 F3 = YES Update F5 F2= +SF(value) Update F5 F2= -SR(value) Update F3,F1,F4,F5 EXIT (abort) N EOV / EOF Y Update F8 (value from Report #3) N Dup.Blocks in Report #3? Adjust values related to file segment containing dup.blocks, then adjust others values in trace table Y #BC + #RE = BlockCount? Identify Unrecoverable Blocks Y N Report the problem to emag and ask for redo the job or more explanations on problem encountered END

26 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 F and 30-35% humidity. Rewind/retension all media types. Migrate E-records from legacy media formats to newer formats.

27 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