If you reject a create (allocate) request in IGGPRE00, create (allocate) provides either return code X'B0' or X'B4' to its caller. You can write IGGPRE00 to provide a reason code in the IEXREASN field of the parameter list, which create returns to its caller along with the X'B0' or X'B4' return code. The reason code appears as the last two bytes of the diagnostic information displayed as part of message IGD17040I.

Scheduler allocation treats return code X'B0' from allocate as an unconditional rejection of the allocate request. Scheduler allocation treats X'B4' as a conditional rejection of the allocate request, only rejecting 'the request' for the volume being processed. If the allocate request is not for a specific volume, another volume can be chosen and the allocate function retried.