How to destroy data on backup tapes

What you will learn: This tip offers guidelines for destroying data on backup tapes, with information about

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degaussing, tape cartridge destruction, tape reuse and record keeping.

Although data left on discarded hard drives gets a lot more publicity, data on discarded tapes is potentially a bigger issue. Most organizations discard tapes before they start having problems and there is a vigorous market in used tapes and cartridges. If the data on those tapes is still readable -- that can be a major problem.

The most common method of destroying data on tapes is degaussing -- exposing the tape to a powerful magnetic field to scramble the data. If it's done properly, degaussing effectively destroys the data on tapes and allows reuse of tapes that don't have prewritten servo tracks. If the tape technology uses magnetic servo tracks, they also will be destroyed and the tape will be rendered useless.

Note, however, that degaussing has to be performed properly. The tapes need to be exposed to a strong enough magnetic field for the correct amount of time to completely destroy the data. Tapes differ significantly in how strong the magnetic field needs to be. For example, tapes with higher data densities generally need stronger fields because the magnetic particles have greater coercivity (are harder to magnetize and demagnetize). Tape maker Imation Corp. ran tests on its cartridges and found that a magnetic field that took most of the data off its 3940E cartridge left its 9840 cartridge readable in a normal drive. Always remember that the degausser has to be matched to the specific kind of tape being destroyed.

Also, because it can take two-to-five minutes and sometimes multiple passes through the degausser to make sure a tape is properly destroyed, there's a temptation to gain speed at the expense of certainty by cutting down on the degaussing cycle or putting more tapes than specified in the device at once. It's important that the manufacturer's recommendations be followed carefully.

Another thing to consider is whether you want to try to reuse the media. This applies mostly to tapes that were written once or a few times for archival purposes. Tapes used for daily or weekly backups often don't have enough life left in them to reuse reliably.

The common rule is that tapes containing highly confidential data should not be reused. Those tapes should be physically destroyed after they have been erased. Many tape degaussers offer an option to physically destroy the tape, as well as erasing it by methods such as punching holes in the cartridge.

Selling your used tapes is even more contentious because of the possibility that some of your data will be readable when the tape is resold. Imation and other tape manufacturers have made much of this possibility recently. Some vendors of used tape, such as Graham Magnetics disagree. It claims that not all resellers properly erase their tapes, and if a tape is properly erased, it is unreadable and not a danger.

Finally, record keeping and auditing is almost as important as destroying the data. Keep complete and auditable records of what was destroyed and when. If you have a third party handle the destruction, make sure you get, and keep, certificates of destruction on the data.

There are a number of companies that offer tape erasing and destruction services. For example, Media Recovery offers secure destruction of data on both servo and nonservo tapes. The company overwrites the data tracks on servo tapes so the tapes can be reused. StorageMedia purchases used tapes, destroys the data on them, including providing certificates of destruction, and resells the media or donates it to a specified charity.

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

This was first published in June 2007

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