Establishing a Backup Schedule
The frequency with which you create backups depends on how often your data changes and how valuable your data is. You can perform a weekly backup, a monthly backup, and an archive backup. The archive backup can be a simple copy.
The 12-week schedule uses a different backup tape each day for two weeks, with the first tape being used again at the beginning of every third week. Incremental backups are performed Monday through Thursday, and normal backups are performed Friday, with the most recent normal backup stored on-site, as illustrated in Figure 12.3. The normal backup of the preceding week is stored off-site. At the end of 12 weeks, the cycle starts again with a new set of tapes.
Figure 12.3 Backup Rotation for a 12-Week Schedule
One popular tape-alternation schedule uses 19 tapes over the course of one year. Four tapes are used Monday through Thursday for incremental backups, and three tapes are used for the normal backups performed each Friday. Figure 12.4 shows one month of the 12-month schedule. The remaining 12 tapes are used for monthly normal backups that are stored off-site.
Figure 12.4 Backup Rotation for One Month in a 12-Month Schedule
You can lower backup costs by alternating backup media. The life cycle of a tape depends on the manufacturer and on storage conditions.