VSAM data sets can be defined with either the DEFINE CLUSTER command
or the ALLOCATE command. When a cluster is defined, VSAM uses the
following catalog entries to describe the cluster:
- A cluster entry describes the cluster as a single component.
- A data entry describes the cluster's data component.
- For a key-sequenced data set, an index entry describes the cluster's
index component.
All of the cluster's attributes are recorded in the catalog.
The information that is stored in the catalog provides the details
needed to manage the data set and to access the VSAM cluster or the
individual components.
If you use DEFINE CLUSTER, attributes of the data and index components
can be specified separately from attributes of the cluster.
- If attributes are specified for the cluster and not the data and
index components, the attributes of the cluster (except for password
and USVR security attributes) apply to the components.
- If an attribute that applies to the data or index component is
specified for both the cluster and the component, the component specification
overrides the cluster's specification.
If you use ALLOCATE, attributes can be specified only at the cluster
level.