Sizing the RCDS

Use this formula to estimate the size of your RCDS.

nvsam × nopen × ndays × 8192 bytes
Where:
  • nvsam is the number of VSAM data sets
  • nopen is the average number of times a VSAM file is opened or closed per day
  • ndays is the number of days of log information you want to keep

For example, if you have 100 VSAM data sets that are opened or closed 10 times each per day and the information is kept for 30 days, calculate the approximate size of the RCDS as follows:

100 x 10 x 30 x 8192 bytes = 245,760,000 bytes

You can estimate the size of your RCDS as 245 megabytes.

IBM® recommends that you make one of the recovery control data sets smaller than the other two. If the smaller one becomes full, CICS® VR issues messages warning you that your smaller RCDS is full, then continues using the larger RCDSs. This warning notifies you that your RCDS needs maintenance and lets you take action before all three RCDSs are full and halts recovery. See Maintaining the RCDS for more information.