Using Object, Object Backup, and Tape storage groups

In addition to the storage groups that are defined by each installation for its data sets, OAM uses three special storage group types: Object, Object Backup, and Tape. OAM uses these storage groups as follows:

An Object storage group contains primary objects. See Assigning Object Storage Groups for more information on assigning storage groups.
An Object Backup storage group contains the first or the second backup copy of each object for which the management class construct requires a backup. See Assigning Object Backup storage groups for more information on assigning Object Backup storage groups.
A Tape storage group contains tape volumes that are associated with an automated tape library dataserver (ATLDS) or a manual tape library (MTL). See Assigning Tape Storage Groups for more information on assigning storage groups.

A primary object is the primary copy of an object in the object storage hierarchy, which is stored in the Object storage group on a disk sublevel (DB2 or file system), optical, or tape. A backup object is the first backup copy of an object, which is stored in the Object Backup storage group specified as a first backup storage group. A second backup object is the second backup copy of an object, which is stored in the Object Backup storage group specified as a second backup storage group.

You can retrieve the primary, backup, or second backup copy of an object by using the OSREQ RETRIEVE command. Specify VIEW(PRIMARY), VIEW(BACKUP), or VIEW(BACKUP2) on the RETRIEVE request. You can also get automatic access to the backup copies for retrieval by using the Automatic Access to Backup facility.

When a primary or backup copy of an object residing on optical or tape media is retrieved, OAM can also create a temporary copy of the object in disk sublevel 1 or disk sublevel 2 for a user-defined number of days. This can significantly improve the performance rate for subsequent retrieves of this object. This object recall to disk process can be initiated explicitly using a RECALL keyword on the OSREQ RETRIEVE request, or implicitly using defaults defined through SETOSMC statements in the CBROAMxx Parmlib member. Refer to Recalling objects to disk for details.

Related reading: See z/OS DFSMS OAM Application Programmer's Reference for more detailed information on the OSREQ macro.