A backup volume is an optical volume that is associated with an Object Backup storage group. Backup volumes are usually intended to provide disaster recovery or to meet legal storage requirements. They contain backup copies of objects whose primary copies reside elsewhere in the object storage hierarchy. OAM can create up to two backup copies of an object. A primary copy of an object resides on a grouped volume; backup copies reside on backup volumes.
A scratch volume becomes a backup volume when it is used by OAM to satisfy a write request for the Object Backup storage group. When a scratch volume becomes a backup volume, both volumes on the optical disk become backup volumes.