Backing up to multiple DASD data sets

If you decide to back up the control data sets and journal data set to DASD, you must first allocate and catalog a backup data set for each backup version of the control data sets. If the CDS is multicluster, additional backup version data sets are required. See Considerations when using multicluster control data sets.

The following example describes the process of backing up the control data sets and journal data set to multiple DASD backup data sets. The example assumes you have single-cluster control data sets.

1. The following command has been specified to indicate the number of preallocated data sets for each control data set and the journal data set:

   SETSYS CDSVERSIONBACKUP(DATAMOVER(DSS) -
        BACKUPCOPIES(3) -
        BACKUPDEVICECATEGORY(DASD) -
        MCDSBACKUPDSN(BHSM.MCDS.BACKUP) -
        BCDSBACKUPDSN(BHSM.BCDS.BACKUP) -
        OCDSBACKUPDSN(BHSM.OCDS.BACKUP) -
        JRNLBACKUPDSN(BHSM.JRNL.BACKUP))

   BACKUPCOPIES(3) indicates the number of preallocated data sets for each backup data set.

2. Three backup data sets are allocated for each control data set and the journal data set backup copy. Assume the following 12 data sets are allocated:

   Copy Number	Names of Allocated Backup Data Sets
   1	BHSM.MCDS.BACKUP.V0000001 BHSM.BCDS.BACKUP.V0000001 BHSM.OCDS.BACKUP.V0000001 BHSM.JRNL.BACKUP.V0000001
   2	BHSM.MCDS.BACKUP.V0000002 BHSM.BCDS.BACKUP.V0000002 BHSM.OCDS.BACKUP.V0000002 BHSM.JRNL.BACKUP.V0000002
   3	BHSM.MCDS.BACKUP.V0000003 BHSM.BCDS.BACKUP.V0000003 BHSM.OCDS.BACKUP.V0000003 BHSM.JRNL.BACKUP.V0000003

   Note:

   1. The final qualifier of each backup data set must start with V0000001 and increase by 1 for each required backup data set. Because you chose DSS as the data mover in the SETSYS CDSVERSIONBACKUP command, DFSMShsm changes the final qualifier of its output data sets to begin with the letter D (D0000001). The renaming of the backup data set final qualifier happens automatically when you change data movers.
   2. If the journal is allocated as a large format sequential data set and is larger than 64K tracks, when you preallocate the journal backup data set, you must allocate the journal backup data set as a large format sequential data set, which is large enough to contain a copy of the original large format sequential journal.
3. DFSMShsm backs up the control data sets and journal data set by doing the following:
   1. It issues an exclusive enqueue against the control data set resource and, if it is in a multiple DFSMShsm-host environment, reserves the volumes containing the journal data set and each control data set being used.

      When using RLS in a multiple DFSMShsm-host environment, DFSMShsm does an exclusive enqueue rather than a reserve.

   2. It invokes DFSMSdss to logically dump each of the control data sets, using concurrent copy if available. DFSMSdss informs DFSMShsm when a concurrent copy session has been established, or when it has finished the dump of a control data set.
   3. It copies the journal to the backup data set and nulls the journal data set. When the journal has been backed up and all the concurrent copy sessions have been established or all the control data sets have been backed up, DFSMShsm releases the volume reserves (if using RLS there are no reserves), and dequeues the control data set resource.

      When DFSMShsm backs up the control data sets and journal data set, it determines the final qualifier of the backup data sets. If the version number in the final qualifier matches the version number in the final qualifier of an existing data set, DFSMShsm uses the existing data set. In this example, DFSMShsm finds an existing backup data set the first three times it backs up the control data sets, and changes the first letter of the last data set name qualifier from V to D (V0000001 becomes D0000001). The fourth time DFSMShsm backs up the control data sets, it cannot find an existing version 4 backup data set. Therefore, DFSMShsm backs up the control data sets to the backup data set with the final qualifier of D0000001.

   4. If DFSMShsm backs up the control data sets to DASD volumes and needs to rename the backup data set, it does so. In this example, after DFSMShsm successfully backs up these data sets for the fourth time, it renames the backup data set by changing the final qualifier of D0000001 to a final qualifier of D0000004. Even if the renaming fails, the backup copy is still valid.
   5. DFSMShsm optionally calls the control data set backup user exit ARCCBEXT, allowing you to process the backup version after DFSMShsm creates it.

If you change the specification for the number of backup copies kept to increase the number of copies, you must first allocate and catalog additional backup data sets. Start with a final qualifier that is one more than the last final qualifier of your backup data sets on DASD.