Magnetic tape used for backup and data storage is remarkably tough stuff, but it is not invulnerable. Temperature variations between the tape and the operating environment can result in errors and an unreadable tape. If the tape is exposed to different conditions in shipping or storage, it will need time in the operating environment to reach equlibrium.
Theoretically, tape should be kept at a temperature of about 72 degrees Fahrenheit and a relative humidity of about 40% at all times. Many enterprises maintain climate-controlled tape vaults for this reason, but for companies that don't, controlling the environment for the tape during transport is notoriously a problem.
For example, for IBM's 20/40 GB internal 4 mm tapes, the company recommends acclimatization if the tape has been exposed to humidity or temperature differences of more than 20 degrees F (11 C). The acclimatization period should be for as long as the tape was out of the operating environment or 24 hours, whichever is less.
A word of warning: Don't go by how warm the cartridge feels. The tape cartridge's case warms up fairly quickly, but the tape itself takes longer to adapt, with the tape closest to the reel taking the longest of all.
The rule of thumb for acclimatizing tape is to wait 24 hours before mounting the tape. This is a safe guide, but it may be longer than necessary.
If possible, try to ensure that tapes needed immediately, such as those for a restore, are transported under climate control so they will not need acclimatization. This can be expensive, but under the right circumstances (for restoration or disaster recovery, for example), it can be worthwhile.
While these rules of thumb are useful, you should also check with your tape manufacturers for their acclimatization recommendations.
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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