In April 2007, I backed up a large amount of scanned files. This fit on one tape (approximately 360 GB). We're now trying to do some further processing on these scans but in trying to restore the files, the images have digital corruption noise going across the images (like static). This is about 40,000 scans and they're all like this. I know they were fine on the RAID set before it was backed up. I tried restoring to different storage locations, rebuilding the catalog from the tape, cleaning the tape drive, tried a different backup library, etc. I'm using EMC Corp. Retrospect 7.5 with an Overland Storage NEO 2000 LTO-3 library. Is it possible that the tape is dirty? When it was backed up, there were no errors from Retrospect. Any ideas?

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What you're describing is a very unusual problem. It's also very difficult to determine the root cause of this type of problem without full diagnostic information. The most frequent problems encountered with image data during backups are usually associated compression. Imaging data doesn't compress very well (if at all) and it's usually advisable to turn compression off at the software or hardware level. That said, if you had compression on before and backup data was restored without a problem, then compression issues can be ruled out.

As you suggest, there might be something wrong with the tape media, but I can't remember having ever encountered a "dirty tape" before.* Typically, faulty tapes will result in I/O errors that are detected at the hardware or software level. I would suggest that you contact both the drive and tape manufacturer to see if they have encountered similar issues in the past and if so, what their fix was.

Hopefully, you've followed backup best practices and you have more than one copy of your backup data for disaster recovery purposes. Using an offsite copy of your backup data should either resolve the issue or point to a hardware or software failure if the condition persists.

*In my original response, I mentioned that I could not remember having ever encountered a "dirty tape" before. That said, because I have not encountered this problem before does not mean it is not possible. A reader who is in the tape cleaning business was kind enough to inform me that this problem can surface from time to time and is not that unusual. It is apparently a result of "environmental and physical stress under which the tape is expected to perform," which can apparently be resolved through a tape cleaning process. The reader works for a company called Bow Industries that offers tape cleaning services.

This was first published in May 2008

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