Naming a Cluster

You specify a name for the cluster when defining it. Usually, the cluster name is given as the dsname in JCL. A cluster name that contains more than 8 characters must be segmented by periods; 1 to 8 characters can be specified between periods. A name with a single segment is called an unqualified name. A name with more than 1 segment is called a qualified name. Each segment of a qualified name is called a qualifier.

You can, optionally, name the components of a cluster. Naming the data component of an entry-sequenced cluster or a linear data set, or the data and index components of a key-sequenced cluster, makes it easier to process the components individually.

If you do not explicitly specify a data or index component name when defining a VSAM data set or alternate index, VSAM generates a name. Also, when you define a user catalog, VSAM generates only an index name for the user catalog (the name of the user catalog is also the data component name). VSAM uses the following format to generate names for both system-managed and non-system-managed data sets:

If the last qualifier of the name is CLUSTER, replace the last qualifier with DATA for the data component and INDEX for the index component.
```
   Cluster name:  SALES.REGION2.CLUSTER
   Generated data name = SALES.REGION2.DATA
   Generated index name = SALES.REGION2.INDEX
```
ELSE if the cluster name is less than or equal to 38 characters, then append .DATA to the end of the cluster name for the data component and a .INDEX for the index component.
```
   Cluster name:  DEPT64.ASSET.INFO
   Generated data name = DEPT64.ASSET.INFO.DATA
   Generated index name = DEPT64.ASSET.INFO.INDEX
```

ELSE if the cluster name is between 39 and 42 characters inclusive, then append a .D to the end of the cluster name for the data component and a .I for the index component.

   Cluster name:  DEPTABCD.RESOURCE.REGION66.DATA1234.STUFF
   Generated data name = DEPTABCD.RESOURCE.REGION66.DATA1234.STUFF.D
   Generated index name = DEPTABCD.RESOURCE.REGION66.DATA1234.STUFF.I

ELSE if the name is longer than 42 characters, and the last qualifier is not CLUSTER, use the first (N-1) qualifiers of the cluster, alternate index, or user catalog name up to the first four qualifiers, and append as many 8-character qualifiers as necessary to produce a 5-qualifier name.
```
   Cluster name:  DIV012.GROUP16.DEPT98.DAILYLOG.DEC1988.BACK
   Generated data name = DIV012.GROUP16.DEPT98.DAILYLOG.TY7RESNO
   Generated index name = DIV012.GROUP16.DEPT98.DAILYLOG.YIIQHNTR
```

After a name is generated, VSAM searches the catalog to ensure that the name is unique. If a duplicate name is found, VSAM continues generating new names using the format outlined in 4 until a unique one is produced.