A backup tape that cannot be read is useless. It is a good idea to clean and check your tape drives periodically to ensure correct operation. See your hardware manuals for instructions on procedures for cleaning a tape drive. You can check your tape hardware by:
Copying some files to the tape, reading them back, and then comparing the original with the copy.
Or, you could use the -v option of the ufsdump command to verify the contents of the media with the source file system. The file system must be unmounted or completely idle for the -v option to be effective.
Be aware that hardware can fail in ways that the system does not report.
Always label your tapes after a backup. If you have planned a backup strategy similar to those suggested in Chapter 42, Backing Up and Restoring File Systems (Overview), you should indicate on the label "Tape A," "Tape B," and so forth. This label should never change. Every time you do a backup, make another tape label containing the backup date, the name of the machine and file system backed up, backup level, the tape number (1 of n, if it spans multiple volumes), plus any information specific to your site. Store your tapes in a dust-free safe location, away from magnetic equipment. Some sites store archived tapes in fireproof cabinets at remote locations.
You should create and maintain a log that tracks which media (tape volume) stores each job (backup) and the location of each backed-up file.