ABCs of z/OS System Programming Volume 3 - IBM Redbooks

► Physical errors
The records on the DASD volume are invalid; for example, they are of a wrong length.
Reasons can be an overlay of physical DASD space or wrong extent information for the
data set in the VTOC or VVDS.
When errors in the VSAM structure occur, they are in most cases logical errors for the BCS.
Because the VVDS is an entry-sequenced data set (ESDS), it has no index component.
Logical errors for an ESDS are unlikely.
You can use the IDCAMS EXAMINE command to analyze the structure of the BCS. As
explained previously, the BCS is a VSAM key-sequenced data set (KSDS). Before running the
EXAMINE, run an IDCAMS VERIFY to make sure that the VSAM information is current, and
ALTER LOCK the catalog to prevent update from others while you are inspecting it.
With the parameter INDEXTEST, you analyze the integrity of the index. With parameter
DATATEST, you analyze the data component. If only the index test shows errors, you might
have the chance to recover the BCS by just running an EXPORT/IMPORT to rebuild the index. If
there is an error in the data component, you probably have to recover the BCS as described
in 6.14, “Recovery procedures” on page 355.
Catalog errors
By catalog errors we mean errors in the catalog information of a BCS or VVDS, or
unsynchronized information between the BCS and VVDS. The VSAM structure of the BCS is
still valid, that is, an EXAMINE returns no errors.
Catalog errors can make a data set inaccessible. Sometimes it is sufficient to delete the
affected entries, sometimes the catalog needs to be recovered (see 6.14, “Recovery
procedures” on page 355).
You can use the IDCAMS DIAGNOSE command to validate the contents of a BCS or VVDS. You
can use this command to check a single BCS or VVDS and to compare the information
between a BCS and multiple VVDSs.
For various DIAGNOSE examples, see z/OS DFSMS Access Method Services for Catalogs,
SC26-7394.
358 ABCs of z/OS System Programming Volume 3