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 on 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.