How the Retention Policy Works

The Backup media retention policy specifies a period of time during which backed-up data is protected from accidental overwrite. After the retention period is exceeded, the save set is eligible to change its status from recoverable to recyclable. The save set's status, however, does not change to recyclable until it and all the save sets that depend on it have passed their retention policy. Backup keeps track of save set dependencies regardless of whether the dependent save sets are stored on the same media volume or on different volumes. The expiration of a save set's retention policy does not remove the save set's entries from the media database.

When the retention policy for every save set on a volume expires and the status for every save set on a volume changes from recoverable to recyclable, Backup changes the mode of that storage volume to recyclable. Since a volume can contain save sets from multiple backup sessions, all with different retention policies, the mode of a volume might not change to recyclable for a long time. The term "recyclable" is best understood as "eligible for recycling."All the data on the volume remains available for recovery using either save set recover or the scanner command. All the entries for "recyclable" save sets remain in the media database.

The change in status to recyclable is a passive reminder that you can overwrite the volume if conditions are right. If you place the volume in an autochanger or mount the volume in a standalone device and enable the auto media management attribute in the Devices resource, the volume is available for relabel and use by Backup. The existing data is nonrecoverable after the volume is relabeled, so the entries for the overwritten save sets are removed from the media database. For more details about this feature of auto media management, see "How Backup Selects a Storage Volume for Relabeling ".

The save set's entries are also removed from the media database when you manually delete a volume from the Backup volume inventory. However, the data on a volume that you delete manually is still available for recovery using the scanner program. The scanner program retrieves the information needed to re-create entries in either the client file index, in the media database, or in both places. If you re-create the entries in the client file index, a user with the proper permissions can recover data through the Backup recover program (nwrecover). If you re-create the save set's entries in the media database, a user with Backup administration privileges can recover data with save set recover. See Appendix B, Command Line Reference Utilities, or refer to the scanner man page for more information on how to use the scanner program.

Figure 5-3 illustrates how a retention policy works. In this example, the backup cycle is set at one week and the retention policy is set at three weeks.

Figure 5-3 One Week Backup Cycle; Three Week Retention Policy

The save set entries for Week 1 have passed their browse policy and retention policy, but they remain available for recovery using the scanner program until you relabel. When all the save set entries on a volume change status to recyclable, the volume mode changes from full or appendable to recyclable, and the volume is ready to be relabeled for reuse. When you relabel the volume, the data on the volume can no longer be recovered by Backup.

For more information about storage volume modes, see Table 4-3.

For more information about schedules, see "Schedule Configuration ", and for more information about backup levels, see "Backup Levels ".