2. PLANNING › 2.2 Supported MVS Data Structures › 2.2.2 Indexed VTOC Support

2.2.2 Indexed VTOC Support

VCC also scans VTOCs that have an index.  This is valid only
if the VTOC has been converted to have an index associated
with it.

An indexed VTOC is comprised of two elements:  the VTOC
itself and its associated index.  The VTOC is structured in
the same way that a standard VTOC is structured with the
following exceptions:

    o  The Format 4 DSCB will no longer contain the CCHHR
       pointer to the last-used Format 1 DSCB and the number
       of free DSCBs.  This information is kept in the index
       and is retrieved using the CVAF interface.

    o  Volume free space extents are no longer kept in the
       Format 5 DSCB.  There is a record in the index that
       contains a bit map of the used tracks on the volume.
       There is still one Format 5 DSCB in the VTOC.  It
       follows the Format 4 DSCB and contains no information.
       Its sole purpose is to provide a means by which an
       indexed VTOC can be converted back to a standard VTOC.