Real-Time Data Set Stacking Under JES3

JES3 normally issues all tape mount requests in immediate mode at the beginning of a job. However, it is possible to implement Real-time data set stacking under JES3.

In order to implement Real-time data set stacking mount requests under JES3, the mount requests must be intercepted and modified. Use JES3 sample Exit IATUX06 to perform the necessary modifications.

When a job starts, Exit IATUX06 analyzes all tape requests in the job. The exit changes mount requests to DEFERRED mode and issues a message if:

• The data set that is to be created is a candidate for stacking.
• The mount request is in immediate mode (meaning, DEFER is not specified).

When the data set is created, Control-M/Tape searches for an appropriate volume and issues a mount message.

A data set is a candidate for stacking if all of the following are true:

• The request is for a scratch tape.
• Control-M/Tape is active and real-time data set stacking is enabled (meaning, the DYNSTK installation parameter is set to Y).
• A corresponding Control-M/Tape rule has been defined and is active. This rule must include a DO STACK=Y statement.

Note: Under JES3, the DO STACK=Y statement can only be specified with selection criteria ON DATASET, ON JOBNAME and/or ON USERID.