About assigning and deassigning volumes
An assigned volume is one that is reserved for exclusive use by NetBackup. A volume is set to the assigned state when either application writes data on it for the first time. The time of the assignment appears in the Time assigned column for the volume on the Volumes tab. When a volume is assigned, you cannot delete it or change its volume pool.
A volume remains assigned until NetBackup deassigns it.
NetBackup deassigns a volume only when the data is no longer required, as follows:
For regular backup volumes, when the retention period has expired for all the backups on the volume.
For catalog backup volumes, when you stop using the volume for catalog backups.
To deassign a volume, you expire the images on the volume. After you expire a volume, NetBackup deassigns it and does not track the backups that are on it. NetBackup can reuse the volume, you can delete it, or you can change its volume pool.
You can expire backup images regardless of the volume state (Frozen, Suspended, and so on).
NetBackup does not erase images on expired volumes. You can still use the data on the volume by importing the images into NetBackup (if the volume has not been overwritten).
See About importing backup images.
Note:
It is not recommended that you deassign NetBackup volumes. If you do, be certain that the volumes do not contain any important data. If you are uncertain, copy the images to another volume before you deassign the volume.