You might find it beneficial to merge catalogs if you have many small or seldom-used catalogs. An excessive number of catalogs can complicate recovery procedures and waste resources such as CAS storage, tape mounts for backups, and system time performing backups.

Merging catalogs is accomplished in much the same way as splitting catalogs. The only difference between splitting catalogs and merging them is that in merging, you want all the entries in a catalog to be moved to a different catalog, so that you can delete the obsolete catalog.

The following steps should be followed to merge two catalogs:

1. Use ALTER LOCK to lock both catalogs.
2. Use LISTCAT to list the aliases for the catalog you intend to delete after the merger. Use the OUTFILE parameter to define a data set to contain the output listing.
3. Use EXAMINE and DIAGNOSE to ensure that the catalogs are error-free. Fix any errors indicated.
4. Use REPRO MERGECAT without specifying the ENTRIES or LEVEL parameter. The OUTDATASET parameter specifies the catalog that you are keeping after the two catalogs are merged. This step can take a long time to complete.
5. Use the listing created in step 2 to create a sequence of DELETE ALIAS and DEFINE ALIAS commands to delete the aliases of the obsolete catalog, and to redefine the aliases as aliases of the catalog you are keeping.

   If this step fails for any reason, see Recovering from a REPRO MERGECAT Failure.

6. Use DELETE USERCATALOG to delete the obsolete catalog. Specify RECOVERY on the DELETE command.

   If your catalog is shared, run the EXPORT DISCONNECT command on each shared system to remove unwanted user catalog connector entries.

7. Use ALTER UNLOCK to unlock the remaining catalog.

You can also merge entries from one tape volume catalog to another using REPRO MERGECAT. REPRO retrieves tape library or tape volume entries and redefines them in a target tape volume catalog. In this case, VOLUMEENTRIES needs to be used to correctly filter the appropriate entries. The LEVEL parameter is not allowed when merging tape volume catalogs.