Defining the Storage Management Subsystem Configuration

An SMS configuration is composed of a set of data class, management class, storage class, storage group, optical library and drive definitions, tape library definitions, and ACS routines to assign the classes and groups. It also includes the aggregate group definitions and the SMS base configuration. The SMS base configuration contains default information such as default management class and default device geometry. It also identifies the systems and system groups (or a combination of both) in the installation for which the subsystem manages storage.

This information is stored in SMS control data sets, which are VSAM linear data sets. You can define these control data sets using the access method services DEFINE CLUSTER command.

Related Reading: For detailed information on creating SMS control data sets, see z/OS DFSMSdfp Storage Administration.

You must define the control data sets before activating SMS. Although you only need to allocate the data sets from one system, the active control data set (ACDS) and communications data set (COMMDS) must reside on a device that can be accessed by every system to be managed with the SMS configuration.

SMS uses the following types of control data sets:

Source Control Data Set (SCDS)

This contains the information that defines a single storage management policy, called an SMS configuration. You can define more than one SCDS, but only one can be used to activate a configuration at any given time.

Active Control Data Set (ACDS)

This contains the output from an SCDS that has been activated to control the storage management policy for the installation. When you activate a configuration, SMS copies the existing configuration from the specified SCDS into the ACDS. By using copies of the SMS classes, groups, volumes, optical libraries, optical drives, tape libraries, and ACS routines rather than the originals, you can change the current storage management policy without disrupting it. For example, while SMS uses the ACDS, you can perform the following actions:

Create a copy of the ACDS
Create a backup copy of an SCDS
Modify an SCDS
Define a new SCDS

The ACDS must reside on a shared device to ensure that all systems in the installation use the same active configuration.

Communications Data Set (COMMDS)

Contains the name of the ACDS and enables communication between SMS systems in a multisystem environment. The COMMDS also contains space statistics, SMS status, and MVS™ status for each system-managed volume.

Recommendation: Although only one COMMDS is used at a time for an SMS installation, ensure that you have more COMMDSs on different volumes for recovery purposes.