Because the physical and logical description of a VSAM data set is contained in its catalog entries, VSAM requires up-to-date catalog entries to access data sets. If either your data set or your catalog is damaged, your recovery procedure must match both data set and catalog entry status. Recovery by reloading the data set automatically takes care of this problem. A new catalog entry is built when the data set is reloaded.

Backing up the data sets in a user catalog lets you recover from damage to the catalog. You can import the backup copy of a data set whose entry is lost or you can redefine the entry and reload the backup copy.

For information about backing up and recovering a catalog, see z/OS DFSMS Managing Catalogs and z/OS DFSMShsm Managing Your Own Data.