When you define a cluster, you can directly specify certain descriptive, performance, security and integrity information. Other sources provide information you omit or the system does not let you provide.

If the Storage Management Subsystem (SMS) is active, and you are defining a system-managed cluster, you can explicitly specify the data class, management class, and storage class parameters and take advantage of attributes defined by your storage administrator. You can also implicitly specify the SMS classes by taking the system determined defaults if such defaults have been established by your storage administrator. The SMS classes are assigned only at the cluster level. You cannot specify them at the data or index level.

If SMS is active and you are defining a non-system-managed cluster, you can also explicitly specify the data class or take the data class default if one is available. Management class and storage class are not supported for non-system-managed data sets.

If you are defining a non-system-managed data set and you do not specify the data class, you must explicitly specify all necessary descriptive, performance, security, and integrity information through other access method services parameters. Most of these parameters can be specified for the data component, the index component, or both. Specify information for the entire cluster with the CLUSTER parameter. Specify information for only the data component with the DATA parameter and for only the index component with the INDEX parameter. See Using Access Method Services Parameters for an explanation of the types of descriptive, performance, security, and integrity information specified using these parameters.

Both the data class and some other access method services parameters can be used to specify values to the same parameter, for example, the control interval size. The system uses the following order of precedence, or filtering, to determine which parameter value to assign.

1. Explicitly specified DEFINE command parameters
2. Modeled attributes (assigned by specifying the MODEL parameter on the DEFINE command)
3. Data class attributes
4. DEFINE command parameter defaults