The most commonly quoted figure for the archival life of magnetic tape is 30 years. Even in an era of heightened
concern about compliance and records retention, that is long enough to make storage administrators comfortable -- perhaps a little too comfortable.
Data life on magnetic tapes is not a "write-it-and-forget-it" proposition. While it is true that tapes can have a storage life measured in decades, the 30-year figure assumes storage under ideal conditions. For example, the Quantum DLT 8000 data sheet specifies the 30-year lifespan at 20-degrees centigrade and 40% non-condensing humidity. Other manufacturers specify similar conditions. The important thing is that these ranges of temperature and humidity are generally fairly narrow, and the more the storage conditions depart from those ideals, the shorter the life of the tape. Considering the penalties enterprises face if they fail to meet compliance regulations, losing data because of tape degradation is not a good idea.
This has led to the other extreme of storage: rewriting all critical tapes every year to keep the data fresh. Given the volume of critical data in a typical enterprise, that's not a very attractive proposition. Making sure your tapes are current and usable is not that difficult, but it does require some thought, at least in the beginning. The first thing you need to decide is how long to maintain each class of data. Although most businesses keep records for three to seven years, some of the laws require that they retain some information for as much as 30 years, or perhaps longer.
The next steps: Consult with manufacturers and find the ideal storage conditions for each kind of tape your enterprise uses and then establish storage facilities with those conditions. This may involve making two copies of some tapes: a working copy to be kept in a normal environment and one or more archival copies to be kept under tightly controlled conditions. Generally speaking, only a very small fraction of your enterprise's data will need this kind of special care.
In the case of keeping data for extended periods of time, say 10 years or more, you should also plan to rewrite the data at appropriate intervals for safekeeping.
Finally, plan to migrate the data to new technologies. Even 10 years is a long time in the storage industry, and you will probably want to change backup methods at least once or twice in the retention period of the data.
Until recently, the archival life of storage media has been of more concern to librarians and other keepers of audiotape than to data storage professionals. Much of the best work on preserving magnetic tape is in those areas. For example, Vidipax has a paper titled "Magnetic tape preservation tape storage" on its Web site.
About the author:
Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in storage and other computer issues.
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