Determining the Number of Local LUs

The maximum number of local LUs you can define on a z/OS® system is 500, of which up to 200 can be associated with a transaction scheduler. For administration simplicity, you should define the smallest number of LUs that you need for your installation. You must define at least one LU before APPC/MVS processing can take place, even when APPC processing remains on a single system.

Although APPC/MVS requires only one LU to start processing, an installation might need more than one LU for various reasons:

Testing applications— Programmers who use a test system might want a separate LU from which to test applications. The test applications' profiles can be kept in a separate TP profile file as well. After testing the applications, programmers can add the applications' profiles to the production TP profile file.
More than one transaction scheduler— Only one transaction scheduler can be associated with an LU at a time. If your installation uses a transaction scheduler in addition to the APPC/MVS transaction scheduler, define a separate LU for each scheduler.
Isolation of TPs accessed— An LU can be created to provide exclusive access to a group of TPs. TPs are accessed from a single TP profile file named to an LU. To completely isolate a group of TPs from every other LU, place the TP profiles for the TPs in a separate file from other TP profiles, and associate that TP profile file with one specific LU.
To further isolate TPs within the file, coordinate the TP level from its TP profile key with the LU level. For information about levels, see TP Profile Key.
Using APPC/MVS Servers— Servers cannot normally receive inbound requests from LUs that are associated with a transaction scheduler (unless the servers are associated with the scheduler). If your installation uses one or more APPC/MVS servers, define at least one LU that is not associated with a transaction scheduler. Such LUs are called NOSCHED LUs.
Outbound Requests When No Scheduler is Active— To allow TPs to flow outbound allocate requests when no transaction scheduler is active, define one NOSCHED LU.