When you calculate the size of a COMMDS, you have to account for both system and volume information. With SMS 32-name support, the amount of space required for a COMMDS increased. A previously allocated COMMDS might have insufficient space to support the changes. You might need to allocate a new COMMDS prior to activating SMS on a current level system, and you should always review the COMMDS size when migrating from prior DFSMS releases. The following formula helps you determine the size of a COMMDS (VOL = estimated number of DASD volumes in the SMS complex to be managed by SMS):
COMMDS size (bytes) =8192 + (588 * VOL)
For example, if you have 40 DASD volumes in the SMS complex, you need to allocate 31712 bytes for the COMMDS.