Depending on your business environment you might want to control the use of tape resources to allow important jobs to finish quickly. i5/OS™ provides several features for this.
You can use the Change Job Media Library Attributes (CHGJOBMLBA) command to change the priority of tape resource requests for a particular job, and the Work with MLB Resource Queue (WRKMLBRSCQ) command to work with the tape resource manager queue.
The CHGJOBMLBA command allows you to change the resource allocation attributes for your own job or another user's job if you have *JOBCTL special authority. You can use the resource allocation priority to change the priority of requests to use a tape resource within a tape library. You can assign a higher priority to certain jobs to allow them to get a tape resource as soon as one becomes available. You can assign a lower priority to jobs that can wait until all other higher priority jobs finish using the tape resources. Typically, very short-running tape operations such as the dynamic retrieval of an object that was saved storage free should be assigned a high resource allocation priority. Long-running jobs that are not required to finish quickly, such as Duplicate Tape (DUPTAP) or Display Tape (DSPTAP), can be assigned a lower resource allocation priority.
You can also add *MLBA to either the Work with Job (WRKJOB) or Display Job (DSPJOB) command in order to view or adjust your tape library attributes.
The WRKMLBRSCQ command allows you to manipulate the requests to use a tape resource within a tape media library. The WRKMLBRSCQ command shows the resources that are currently processing a request, have a category mounted, or the requests that are waiting to be assigned a tape resource. You can change the resource allocation attributes for requests that are waiting to use a tape resource by using option 2 (Change Request MLB Attributes) on the Work with MLB Resource Queue (WRKMLBRSCQ) display. The attributes for the next request can be changed by using the CHGJOBMLBA command to change the resource allocation attributes for the job that is currently using the tape resource. You can do this by using option 5 (Work with job) on the Work with MLB Resource Queue (WRKMLBRSCQ) display, and then selecting option 21 (Work with media library attributes).
There are times when a request will show a priority of 0. These requests are for when a tape resource is being used by the system for a tape operation. An example is when a tape command using ENDOPT(*UNLOAD) is completed and the system is still unloading the cartridge.
You can use the Retrieve Job Media Library Attributes (QTARJMA) and Change Job Media Library Attributes (QTACJMA) APIs to control tape library attributes programmatically. For a more detailed description and an example, see Control tape library attributes with APIs.