The VVDS contains VSAM volume records (VVRs) that hold information about VSAM data sets residing on the volume. The VVDS also contains non-VSAM volume records (NVRs) for SMS-managed non-VSAM data sets on the volume. If an SMS-managed non-VSAM data set spans volumes, only the first volume contains an NVR for that data set.

The system automatically defines a VVDS with 10 tracks primary and 10 tracks secondary space, unless you explicitly define it. If you want to explicitly define a VVDS, for example, as part of volume initialization, IBM® recommends that you use the default TRACKS(10 10) for the space allocation. If you need a VVDS with more space, there are two approaches to obtaining it:

• The recommended approach is to keep the defaults TRACKS(10,10s) and, if required, obtain more space through secondary allocations as needed. For instance, if you determine that you need a 60 track VVDS, keep the default allocation so that you do not over allocate your VVDS and obtain additional space as required through secondary allocation. This is recommended because a large VVDS allocation can effect performance in some products, ADRDSSU for example, which process the entire contents of the VVDS data set in some functions.
• You can estimate the amount of VVDS space you need to allocate by estimating the number and type of data sets that will reside on the volume. (Note that data sets used by NFS or DFM will have 500 bytes added to their published size to accommodate new cell types) Then, use the information in Table 1 to estimate the total amount of space needed for the data sets that will reside in the VVDS.

  To estimate the total amount of space needed:

  1. Add the space required by each data set.
  2. Add 8 kilobytes for use by the VVDS.
  3. Multiply the result by 1.2 to leave room for errors in the calculation.
  4. Divide the result by 1024 to determine the number of kilobytes, and round up to the nearest integer.

  Specify the result in the KILOBYTES parameter of the DEFINE CLUSTER command. Choose an appropriate secondary space allocation, usually at least half of the primary allocation.