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

Specify SHAREOPTIONS(3,3) for the ACDS and COMMDS. These data sets must be shared
between systems that are managing a shared DASD configuration in a DFSMS environment.
Define GRS resource names for active SMS control data sets
If you plan to share SMS control data sets between systems, consider the effects of multiple
systems sharing these data sets. Access is serialized by the use of RESERVE, which locks
out access to the entire device volume from other systems until the RELEASE is issued by the
task using the resource. This is undesirable, especially when there are other data sets on the
volume.
A RESERVE is issued when SMS is updating:
► The COMMDS with space statistics at the expiration time interval specified in the
IGDSMSxx PARMLIB member
► The ACDS due to changes in the SMS configuration
Place the resource name IGDCDSXS in the RESERVE conversion RNL as a generic entry to
convert the RESERVE/RELEASE to an ENQueue/DEQueue. This minimizes delays due to
contention for resources and prevents deadlocks associated with the VARY SMS command.
Important: If there are multiple SMS complexes within a global resource serialization
complex, be sure to use unique COMMDS and ACDS data set names to prevent false
contention.
For information about allocating COMMDS and ACDS data set names, see z/OS DFSMS
Implementing System-Managed Storage, SC26-7407.
272 ABCs of z/OS System Programming Volume 3