DFSMShsm normally determines that it is in a shared-CDS environment by (1) recognizing startup parameters CDSSHR=YES or RLS, and (2) by examining whether the index component of the migration control data set (MCDS) resides on a DASD volume that has been SYSGENed with a SHARED or SHAREDUP device attribute. If either condition is met, DFSMShsm performs appropriate serialization.

If the control data sets are used by only a single DFSMShsm host but reside on a shared DASD volume, specify CDSSHR=NO to eliminate unnecessary overhead associated with serialization.

If you do not plan to employ RLS, but do plan to share the control data sets using either RESERVE or ENQ methods, you should explicitly specify CDSSHR=YES. This avoids any damage if the DASD volumes are mis-specified as non-shared on one or more of the sharing systems.