Although most people think of magnetic tape as a long-term storage medium, long term doesn't mean 'forever.' Tape deteriorates over time, and the data it contains eventually becomes unreadable, then unrecoverable.
Unreadable data is data that cannot be read by a conventional tape drive but may be recovered with special techniques. Unrecoverable data is gone for good. The tape has become so badly damaged that the data simply isn't there any more.
Tape has become more reliable as time has gone on. . .which simply means that the tapes most at risk are the oldest ones.
So far the organizations hit hardest by this problem are those storing large quantities of production data, such as oil companies with geophysical exploration data, and scientific establishments, including NASA. However, it is a problem for any organization with data in permanent storage.
If you have archival data that must be maintained 'forever', there are several things you can do.
Take care of your tapes.The lifespan of magnetic tape is strongly influenced by its environment, especially factors such as heat and humidity. Storing tapes under proper conditions will greatly extend their lifespan. Ideally the temperature and humidity of long-term tape storage should be monitored by a device that maintains a history of environmental conditions and warns when the acceptable parameters are exceeded.
Test your tapes regularly. The good news about magnetic tape is that it seldom fails all at once. Often you will get warning signs, such as an increase in read errors, months or even years before the tape finally becomes unreadable. If you include your archival tape in your testing program you can transfer the data to a new tape before it becomes critical.
Replace your tapes regularly. Plan on replacing your tapes on a regular cycle, say once every four to five years, as part of your Information Lifecycle Management strategy. (Tapes that are well-cared for should last at least a decade, but there's no point in pushing it.) Putting the data onto new tapes is also a good time to update old tapes to new technologies such as higher capacity tapes or new drives.
Consider alternative storage media.While no storage medium has an infinite life span, some technologies, notably optical disks, have a much longer life expectancy than tape. In fact,some optical media have lifespans approaching a century or more and are much less sensitive to environmental conditions than magnetic tape.
Of course these optical media are more expensive than magnetic tape. This usually means that they will be used only for the most critical archival data.
About the author: Rick Cook specializes in writing about issues related to storage and storage management.