Reasons for recovering the control data sets

Occasionally a control data set becomes unusable by DFSMShsm. For example, a hardware failure or a software logical failure may occur after which DFSMShsm is unable to use a control data set.

When the control data sets are backed up, they constitute a snapshot of the conditions in the system at that time. After the control data sets are backed up, as DFSMShsm continues to process data sets and volumes, the control data sets are continually changing. To make it possible for you to return the control data sets to their condition just before the error, DFSMShsm makes a journal record of each transaction that occurs in the control data sets. If a control data set becomes lost or damaged, you can return it to its correct condition by recovering a backup version of the control data set and applying the appropriate journal.

The CDS recovery process has variations based on which data mover has been used to back up the control data sets. The low-level (final) qualifier of the name of the control data set backup data set indicates which data mover has been used to back it up. A low-level qualifier of Vnnnnnnn indicates that DFSMShsm backed up the data set. A low-level qualifier of Dnnnnnnn indicates that DFSMSdss backed up the data set, and a low-level qualifier of Xnnnnnnn indicates that CDS version backup of the data set failed, regardless of whether DFSMShsm or DFSMSdss was doing the backup.