Selecting volumes for control data sets
SMS control data sets can be either SMS-managed or non-SMS-managed. Initially, you
should ensure that your control data sets have a volume count of one. The volume count can be either
explicitly specified, implied by the number of volumes serials provided, or derived from the data
class assigned to the data set (the greater value of volume count or dynamic volume count). For more
information, see Defining data classes for more information. For SMS control data sets,
the volume count or dynamic volume count must be less than or equal to the number of online volumes
the data set resides on, otherwise, you might receive messages IEF244I and IEF877E.
- You can have your SMS-managed control data sets (SCDS, ACDS, and COMMDS) defined as multivolume. When you define these data sets as multivolume, you must assign a storage class with the guaranteed space attribute. This is because the control data sets are opened in the SMS address space as a non-SMS managed. If guaranteed space is not specified in the storage class, your SMS-managed CDS cannot be extended to a new volume if no candidate volumes with space are already allocated.
- You cannot use dynamic volume count in the data class to allow extends to new volumes for any SMS-managed CDS. This is true when the SMS-managed CDS (SCDS, ACDS, COMMDS) is opened under the SMS address space such as activation or by using the SETSMS commands (COPYSCDS, SAVEACDS).
If you have a multivolume SCDS that you are activating into a single volume ACDS, you might receive an error because the ACDS is not large enough and volumes cannot be dynamically added to it. To bypass this problem, you need to create a new multivolume ACDS and then activate the ACDS and SCDS simultaneously by using the SETSMS command. For more information about the SETSMS command, see Changing Storage Management Subsystem parameters
If your SMS complex includes more than 16 systems, be sure that the ACDS and COMMDS are accessible to every system in the complex. Define your control data sets on volumes that can be attached to more than 16 systems, such as IBM® RAMAC Virtual Array volumes.