Content unrecognized is usually a result of the tape drive not being able to read or recognize the header information on a tape, usually due to problems with the tape or tape drive. However there are two exceptions:
When tapes are written with a drive which utilizes hardware compression and then are inserted in drives that do not utilize hardware compression. Such tapes will appear as 'Content unrecognized' in drives that do not have the ability to read compressed data.
When a tape is written by a utility other than Retrospect it cannot then be read by Retrospect.
If neither of these exceptions apply to your situation read further.
If only the tape or tapes in which you are interested come up "content unknown/unrecognized " then the problem is isolated to the tape(s) in question. You may have a more general problem with the SCSI bus or SCSI device. If it’s just one set of tapes with problems you can try to optimize your chances for recovery or catalog recreation by doing the following even though they are not likely to resolve the problem of a damaged tape:
Clean the drive using a 4mm cleaning cartridge. Your drive manufacturer recommends that you clean the unit once for every 8-10 hours of run time. Once a week is more than enough for most people. Try another tape. If other tapes work then you just have a tape with a spot that’s bad enough to crash your backup.
Remove SCSI devices other than your tape drive from your chain. Another device on your SCSI bus might be interfering with the tape drive’s communication. Make sure your SCSI ID numbers are set correctly. Turn off your Mac and the SCSI devices. Disconnect all SCSI devices except for the tape drive.
Make sure you are using good cables, proper termination and have solid connections between the computer cables tape drive and terminator. You may need to replace the SCSI cable that connects the tape drive to the computer after removing other devices and cables from the SCSI chain.
You might be missing a terminator or have a bad terminator. The last device and ONLY the last device in your SCSI chain might need to be terminated. Try replacing the terminator if you already have one on the chain.
The computer may be having a problem. Install Retrospect on another computer and try the tape drive there as the lone SCSI device.
The drive may be defective. If you have implemented all of the preceding steps and get failures on multiple tapes after changing cables, terminators and computers then the drive (being the only factor that has not changed) is the culprit—send it back to your vendor for repairs.
If the tape(s) still show "content unknown/unrecognized " the last option is to contact a data recovery house. Data recovery tends to be an expensive prospect.
To avoid the problem in the future make sure you have multiple copies of your data on different sets of tapes and rotate your media from time to time. Make sure you are storing the tapes in a secure location protected from excessive humidity temperature direct sunlight and electro-magnetic radiation.
Last Update: February 13, 2012