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

Creating the VTOC and VTOC index
To initialize a volume (prepare for I/O activity), use the Device Support Facilities (ICKDSF)
utility to initially build the VTOC. You can create a VTOC index at that time by using the
ICKDSF INIT command and specifying the INDEX keyword.
You can use ICKDSF to convert a non-indexed VTOC to an indexed VTOC by using the
BUILDIX command and specifying the IXVTOC keyword. The reverse operation can be
performed by using the BUILDIX command and specifying the OSVTOC keyword. For details,
see Device Support Facilities User’s Guide and Reference Release 17, GC35-0033, and
z/OS DFSMSdfp Advanced Services, SC26-7400, for more information about that topic.
VTOC index format-1 DSCB
A format-1 DSCB in the VTOC contains the name and extent information of the VTOC index.
The name of the index must be 'SYS1.VTOCIX.xxxxxxxx', where xxxxxxxx conforms to
standard data set naming conventions and is usually the serial number of the volume
containing the VTOC and its index. The name must be unique within the system to avoid ENQ
contention.
VTOC index record (VIR)
Device Support Facilities (ICKDSF) initializes a VTOC index into 2048-byte physical blocks
named VTOC index records (VIRs). VIRs are used in several ways. A VTOC index contains
the following kinds of VIRs:
► VTOC index entry record (VIER) identifies the location of format-1 DSCBs and the
format-4 DSCB.
► VTOC pack space map (VPSM) identifies the free and allocated space on a volume.
► VTOC index map (VIXM) identifies the VIRs that have been allocated in the VTOC index.
► VTOC map of DSCBs (VMDS) identifies the DSCBs that have been allocated in the
VTOC.
Chapter 2. Data set basics 49