The DFSMShsm control data sets are the resources with which DFSMShsm manages the storage environment. The journal data set receives an entry for each critical update to any CDS. Discussions of the control data sets and the journal are not complete without also discussing the CDS and journal backup copies. By retaining backup copies of the control data sets and the journal, you provide data integrity because you can merge the journal with the control data sets to reconstruct your environment to the point of failure should the control data sets be lost or damaged.

The three DFSMShsm virtual storage access method (VSAM) control data sets are the migration control data set (MCDS), the backup control data set (BCDS), and the offline control data set (OCDS). The MCDS manages migrated data sets, the BCDS manages backup versions and dump copies, and the OCDS manages backup and migration tape volumes. A single journal data set records each update to any of the three control data sets.