You can specify the required space for a catalog in kilobytes, megabytes, tracks, cylinders, or records. This value can be specified directly on the DEFINE USERCATALOG command, or indirectly, through an SMS data class defined for catalogs that contains a space attribute. You can specify the appropriate data class on the DATACLASS parameter, or you can allow the data class ACS routine to assign the appropriate data class.

If you specify space in records, the amount of space is determined by the average record size. This is specified on the RECORDSIZE parameter, and the default is 4086. In general, you should not change the default values for average and maximum record size.

You must always specify a space parameter at the USERCATALOG (cluster) level. Space is allocated to the BCS according to the following rules:

1. If space is only defined as a subparameter of USERCATALOG, the space specified is assigned to the data component of the catalog. Additional space is allocated to the index according to the size of the space request.
2. If space is specified as subparameters of USERCATALOG and DATA, then the data component is assigned the requested space and the index is allocated space according to the space request for DATA. The USERCATALOG space request is ignored.
3. If space is specified as subparameters of USERCATALOG, DATA, and INDEX, then the data and index components are assigned the requested space. The USERCATALOG space request is ignored. If INDEX space is specified, space must also be specified for DATA.

If you are defining the BCS on a volume that does not contain a VVDS, a VVDS is also defined and allocated with the BCS. This implicitly defined VVDS is allocated with a default primary and secondary space amount. The default space allocation will be the values that the operator specified on the most recent F CATALOG,VVDSSPACE command. If that command has not been issued since IPL, the default space allocation will be TRACKS(10 10).

If you want to define a VVDS with a space allocation different from the default, you must define a VVDS on the volume (using DEFINE CLUSTER) before you define the BCS.