Side Information File

When planning the size of the side information file, consider the size of each entry and the number of entries needed. The size of each side information entry does not vary. The side information key is always 112 bytes, and the remainder of the side information is 136 bytes, resulting in a total of 248 bytes for each entry. This number follows the RECORDSIZE keyword in the VSAM file definition.

The number of entries in a side information file depends on the number of partner LUs and the number of unique TP/logon mode combinations. Outbound requests can be made to many destinations and each combination of destination/TP/logon mode needs a separate side information entry and a unique side information key.

Figure 1 shows how outbound requests for two TPs (TP1 and TP2) require five side information entries because of the various combinations of partner LU/TP/logon mode.

Figure 1. Combinations of Partner LUs, TPs, and Logon Modes

                                                     ┌─────────┐
                  { TP-1 ←───── logmode 1 ───────────┤         │
   Partner LU-A   { TP-1 ←───── logmode 2 ───────────┤         │
                  { TP-2 ←───── logmode 1 ───────────┤         │
                                                     │   MVS   │
                                                     │         │
   Partner LU-B   { TP-1 ←───── logmode 1 ───────────┤         │
                  { TP-2 ←───── logmode 1 ───────────┤         │
                                                     └─────────┘

Therefore, to estimate the number of entries for a side information file, add together the number of unique TP/logon mode combinations for each partner LU.

Figure 2. Side Information Estimate

  Partner LU 1:    # unique TP/logon mode combinations
  Partner LU 2:    # unique TP/logon mode combinations
  Partner LU 3:    # unique TP/logon mode combinations
  Partner LU 4:    # unique TP/logon mode combinations
  Partner LU 5:    # unique TP/logon mode combinations
  ...
  Partner LU n:  + # unique TP/logon mode combinations
           ---------------------------
  TOTAL          = # of side information entries

The estimated number of entries is the first number following the RECORDS keyword in the VSAM file definition. The second number following the RECORDS keyword is the additional number of entries that can be added for expansion. For information about how much expansion to allow, see z/OS DFSMS Access Method Services Commands.

SYS1.SAMPLIB member ATBSIVSM contains a sample VSAM definition for a side information file.