Network Data: Tape Reliability
Although tape drives are very reliable, they do run amok once in a while. The problem is that they don’t always tell you when they’re not working. A tape drive (especially the less-expensive Travan drives) can spin along for hours, pretending to back up your data – but in reality, your data isn’t being written reliably to the tape.
In other words, a tape drive can trick you into thinking that your backups are working just fine. Then, when disaster strikes and you need your backup tapes, you may just discover that the tapes are worthless.
Don’t panic! Here’s a simple way to assure yourself that your tape drive is working. Just activate the “compare after backup” feature of your backup software. Then, as soon as your backup program finishes backing up your data, it rewinds the tape, reads each backed-up file, and compares it with the original version on the hard drive. If all files compare, you know your backups are trustworthy.
Here are some additional thoughts about the reliability of tapes:
The compare-after-backup feature doubles the time required to do a backup, but that doesn’t matter if your entire backup fits on one tape. You can just run the backup after hours. Whether the backup and repair operation takes one hour or ten doesn’t matter, as long as it’s finished by the time the network users arrive at work the next morning.
If your backups require more than one tape, you may not want to run the compare-after-backup feature every day. However, be sure to run it periodically to check that your tape drive is working.
If your backup program reports errors, throw away the tape and use a new tape.
Actually, you should ignore that last comment about waiting for your backup program to report errors. You should discard tapes before your backup program reports errors. Most experts recommend that you should use a tape only about 20 times before discarding it.
If you use the same tape every day, replace it monthly. If you have tapes for each day of the week, replace them twice yearly. If you have more tapes than that, figure out a cycle that replaces tapes after about 20 uses.