Relationship of the UNIT and VOLUME Parameters (Non-SMS-Managed Data Sets)

Cataloged Data Sets

When the data set is cataloged, the system obtains unit and volume information

from the catalog. However, if the DD statement for a cataloged data set contains

VOLUME=SER=serial-number, the system does not look in the catalog; in this case,

you must code the UNIT parameter.

Volume References to Cataloged Data Sets

If a data set is to use the same volumes as a cataloged data set, code

VOLUME=REF to refer to the cataloged data set. The system obtains unit and

volume information from the catalog and places the data set on the same volumes.

Overridden Procedure DD Statements

When a step calls a cataloged or in-stream procedure, an overriding DD statement

in the calling step statement can specify a cataloged data set in its DSNAME

parameter. If so, the overriding DD statement should nullify the UNIT and VOLUME

parameters; if it does not nullify them, the system uses the UNIT and VOLUME

parameters on the overridden DD statement and does not search the catalog.

Passed Data Sets

When receiving a data set passed from a previous step, omit the UNIT and

VOLUME parameters. The system obtains unit and volume information from the

passing step. However, if the receiving DD statement contains

VOLUME=SER=serial-number, code the UNIT parameter also.

Earlier DD Statement

If a data set uses the volumes used for a data set in an earlier step, code a

VOLUME=REF parameter to refer to the earlier DD statement. The system obtains

the unit and volume information from the earlier DD statement. Therefore, you can

omit the UNIT parameter. However, to make the system assign more devices or to

influence device allocation, code the UNIT parameter. The system uses the coded

UNIT parameter, if it requests a subset of the unit type in the referenced DD

statement. Otherwise, the system ignores it.