The catalog address space is designed with internal checks that allow it to identify, and subsequently rebuild, damaged catalog control blocks. However, not all problems can be identified.

If you find that attempts to access a particular catalog are resulting in recurrent abnormal endings, rebuild the control blocks in the catalog address space. This should be done using the CLOSE or UNALLOCATE parameters. If the damaged control blocks are for a VVDS, use VCLOSE or VUNALLOCATE.

Each of these parameters causes the control blocks to be released and rebuilt on a subsequent request that tries to access the catalog. Which parameter you use depends on whether you want the catalog unallocated and closed (UNALLOCATE), or closed but left allocated (CLOSE).

When rebuilding the control blocks for a VVDS, use VCLOSE whenever possible. With VCLOSE, you specify the particular VVDS whose control blocks you suspect are in error. VUNALLOCATE can also be used, but this parameter unallocates all VVDSs. You cannot unallocate a specific VVDS.

The UNALLOCATE parameter can be used to unallocate all catalogs at once. It can also be used to unallocate a catalog on a volume that you need to vary offline. Use VUNALLOCATE if you need to unallocate a VVDS to get a volume offline.