I don't know how VMTAPE co-operates with IBM ATL. We learned a quite some details about VMTAPE's interaction with STK when our environment became mixed, that is with high capacity cassettes/drives and standard cassettes/drives. Furthermore, we have two STK silos and more VM systems than STK could support on its 3270 interface. So, our setup is as follows: all VM systems can reach all drives, but on each VM system STKACS is connected to one robot only. So, to VMTAPE half the drives appear as STK drives, the others as manual drives.
We learned that VMTAPE first questions STKACS to know if it knows a given volser. If yes, STKACS returns all addresses of drives where that volser can technically be mounted. Then VMTAPE uses STAM to select one of those drives and asks STK to mount the volser there. If it is not a volser known to STK, VMTAPE thinks it must be a manual mount and displays "VMTMAN280A Mount ...", which we intercept and send to a VM system connected to the other silo. You may be tempted to code an ALLOCATE exit. Know than that this exit is only called when mounting a scratch tape, not when mounting a specific volume. So we found out it couldn't help us, but after all we didn't need it. Only SCRPOOL ASSIGN was required to trigger silo selection based on dataset name. Kris Buelens
