When a catalog is defined on a volume, a VSAM sphere record is built for the VVDS which resides on the volume with the BCS. This record has the name of the VVDS as its key (SYS1.VVDS.Vvolser).

A catalog has a sphere record similar to other VSAM key-sequenced data sets. This is a self-describing sphere record for the catalog, and contains information about the catalog itself. This sphere record is given a key of binary zeros to ensure it is the first record in the catalog. The data component name for the BCS is the catalog name as you have defined it. A true name record is created for the data and index components. The true name records are related with a key to the catalog name. A record is created to relate the index component to the catalog name of binary zeros, in the same way as for the data component.