Degaussing LTO and 3950 tapes is a no-no

Degaussing used to be the standard way of preparing tapes for re-use. However, LTO and 3950 tapes can't be degaussed and reused, because they contain data they need if they are to function at all.

Degaussing used to be the standard way of preparing tapes for re-use. By passing the tape into and out of a strong magnetic field, the data on the tape could be erased and prepared for rewriting.

Degaussing is still used on some kinds of tapes because it reduces the possibility that previously written data will interfere with new data being written to the tape. However, some kinds of tapes and tape cartridges can't be degaussed and reused, because they contain data they need if they are to function at all.

LTO and 3950 tapes contain pre-recorded servo tracks that keep the tape in synchronization as it passes through the drive. Using servo tracks allows the tapes to record more data by providing feedback to the drive on reading and writing.

Unfortunately, degaussing destroys the servo tracks as well as the recorded information. As a result, a degaussed tape with prewritten servo tracks is useless.

To erase an LTO or other tape with a pre-written servo track without destroying it, use the 'security erase' feature to completely overwrite the data on the tape. Note: Since this means essentially writing the entire tape, it is a time-consuming task.

Of course sometimes you want to render the tape useless. That's why old LTO and 3950 tapes are degaussed before being discarded. Degaussing at the appropriate magnetic flux level (measured in oersteds) effectively destroys all the information on a magnetic tape. Just remember: If you are degaussing old tapes, be careful to do it well away from any tapes you want to keep.

About the author: Rick Cook specializes in writing about issues related to storage and storage management.

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This was first published in October 2006

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