Using a List Generated from the Catalog or the VTOC

There are several considerations to keep in mind when you decide whether to generate a list from the catalog or the VTOC. The source of the list affects the job streams ISMF generates for DUMP and COPY and the way ISMF determines if a data set is multivolume.

Differences between a VTOC List and a Catalog List

Both the DUMP and COPY commands are sensitive to the type of list you use.

If you enter DUMP or COPY on a list generated from the VTOC, ISMF builds a job stream that contains input DD statements for every volume on which the data sets in the list reside. If the data set to be processed is cataloged on another volume, DFSMSdss ignores the cataloged volume and processes the data set from the specified volume. The output is a physical dump in the case of the DUMP operation.

If you use either command on a list generated from the catalog, ISMF does not provide input DD statements for individual volumes. When the DFSMSdss background job executes, DFSMSdss uses a catalog search to determine which volumes the data set resides on. DFSMSdss dumps or copies the data set from all volumes indicated in the catalog. The output is a logical dump in the case of the DUMP operation.

For more information on the difference between a physical and logical dump, refer to z/OS DFSMSdss Storage Administration.

Multivolume Data Sets

The way ISMF determines if a data set is multivolume depends on the source of the list (VTOC or catalog).

A list generated from the VTOC

If you generate the list from the VTOC, ISMF uses the VTOC entry to determine if a data set is multivolume. However, the multivolume information could be incorrect in the following cases:

Data sets that have been defined but unopened can appear in the list as multivolume.
Data sets defined as multivolume can appear as single volume if the second volume has not been used.
VSAM data sets can appear as multivolume data sets since VSAM does not update the FMT1 Data set control block (DSCB).

A list generated from the catalog

If you generate the list from the catalog, ISMF determines if the data set is multivolume by the way the data set is defined in the catalog. ISMF checks for multiple volume serial number entries in the catalog. When the list is built, a data set with more than one volume serial number appears as multivolume. If you define a VSAM data set with the IMBED option, it may appear as multivolume.

ALLOC SPACE value in a catalog generated data set list shows only the prime volser. The candidate volser with guaranteed space is not shown. This is because catalog does not return any space value to ISMF. Catalog returns a space value of zero. ISMF will show the candidate volser when there is data on the volume and catalog returns a space value.