9.3 Care and Feeding of a Tape Drive
Tape drives and tape cartridges are surprisingly durable, but getting the best results requires following a few simple rules:
- Clean the drive regularly!
The most frequent cause of tape drive problems is dirty read/write heads. Tape drive manufacturers typically recommend cleaning the drive monthly or after every 10 to 25 hours of use. It is also a good idea to clean the drive immediately after first using a new tape. Depending on how you use your drive and how clean your environment is, even that may be inadequate. Problems caused by dirty heads are not always immediately obvious, because tape drives use industrial-strength ECC methods that allow them to recover from most read and write errors. The first sign of dirty heads may simply be that backups begin taking longer than they should. If your environment is typical, it's probably not excessive to clean the tape drive weekly or before each full backup. Some drives can be cleaned only by using the recommended cleaning cartridge. Other drives allow you to vacuum or blow out the dust and then use a foam swab moistened with rubbing alcohol to clean the heads and rollers (cotton swabs can leave debris on the heads, and should be avoided). Having once watched a cleaning cartridge destroy the heads on a tape drive, we prefer the second method if the drive manufacturer lists it as permissible.
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Some high-end tape drives keep track of how much the drive has been used since the last cleaning. For example, our Tecmar TS3900i DDS-3 drive generates a warning message in Backup Exec when it is time to clean the drive. Running a cleaning cartridge through the drive clears and resets the timer, and the message disappears until the next time cleaning is due. We've been told that some tape drives simply refuse to operate if you ignore the warning messages too long, but we've never experienced that, simply because we've never risked allowing an expensive drive to go too long without cleaning.
- Avoid exposing tapes to magnetic fields
This should be obvious, but what may not be obvious is that stray magnetic fields from monitors and other peripherals can damage even tapes that are stored some distance from the source. We once found that tapes stored in a desk drawer had been damaged by the field from a monitor sitting on the desk surface above them. For DAT tapes, the only loss is the data stored on the tape, because DAT drives format tapes on the fly as they write the data. For Travan and ADR tapes, any damage is fatal to the tape. These tapes are formatted at the factory, and cannot be reformatted by the user. If you expose a Travan or ADR tape to a magnetic field strong enough to damage the data on it, that tape can no longer be used at all.
- Retension tapes frequently
Periodic retensioning is required by Travan and ADR tapes, but not by DAT tapes. Retensioning simply winds the tape out to the end and then back to the beginning. You should retension a tape before using it for the first time; if it has not been used for a month or more; if it has been shipped (or dropped); or if it has been exposed to a significant temperature change. As a rule of thumb, retension a tape used daily once a week, and one used weekly once a month.
- Store tapes safely
Tapes are quite sensitive to their storage environment, and are happiest at the same levels of temperature and humidity that are comfortable for people. When a tape is not actually in the drive, always replace it in its sleeve or case to avoid dust. Never place a tape in direct sunlight. For safe storage on-site, use a fire safe. Make sure that the safe is rated to store magnetic media. Less expensive fire safes are designed to protect paper, and allow internal temperatures to exceed levels safe for tapes. If the temperature or humidity differs greatly between the storage and use locations, always allow the tape an hour or two to reach equilibrium before using it.
- Replace tapes periodically
Tapes do not last forever. Each time you use a tape, the magnetic medium becomes more abraded and the substrate stretches. For best results, replace tapes every two years or fifty uses, whichever comes first. That is, replace a tape that is used daily at least every two months. Replace a weekly tape at least once a year. Replace a monthly tape at least every two years. In addition to risking the data written to it, using an elderly, worn tape risks damaging the tape drive heads.