About assigning retention periods

The retention period for data depends on the likelihood of restoring information from media after a certain period of time. Some types of data (financial records, for example) have legal requirements that determine the retention level. Other data (preliminary documents, for example) can probably be expired when the final version is complete.

A backup's retention also depends on what needs to be recovered from the backup. For example, if day-to-day changes are critical, keep all the incremental backups in addition to the full backups for as long as the data is needed. If incremental backups only track work in progress toward monthly reports, expire the incremental backups sooner. Rely on the full backups for long-term recovery.

Establish some guidelines that apply to most of the data to determine retention periods. Note the files or the directories that have retention requirements outside of these guidelines. Plan to create separate policies for the data that falls outside of the retention requirement guidelines. For example, place the files and directories with longer retention requirements in a separate policy. Schedule longer retention times for the separate policies without keeping all policies for the longer retention period.

The following table describes recommended retention periods for different types of backups.

The following table suggests several ways that you can prevent backups from expiring earlier than desired.

Another consideration for data retention is off-site storage of the backup media. Off-site storage protects against the disasters that may occur at the primary site.

Regardless of the method that is used for off-site storage, ensure that adequate retention periods are configured. Use the NetBackup import feature to retrieve expired backups.

By default, NetBackup stores each backup on a tape volume that contains existing backups at the same retention level. If a backup has a retention level of 2, NetBackup stores it on a tape volume with other backups at retention level 2. When NetBackup encounters a backup with a different retention level, it switches to an appropriate volume. Because tape volumes remain assigned to NetBackup until all the backups on the tape expire, this approach results in more efficient use of media. One small backup with an infinite retention prevents a volume from being reused, even if all other backups on the volume expired.

To mix retention levels on volumes, select Allow multiple retentions per media in the Media host properties.

If you keep only one retention level on each volume, do not use any more retention levels than necessary. Multiple retention levels increase the number of required volumes.

See Media properties.