CA MIA serializes the device allocations performed by SWAP across all the systems in the MIMplex to prevent tasks on external systems from simultaneously allocating the same device as a local SWAP.
CA MIA serializes SWAP processing across all active systems in the MIMplex by obtaining the device group lock for the device requested on each DDR unit allocation and then plugging the device allocated by SWAP on the external systems.
When CA MIA intercepts a DDR unit allocation request for a potential TO device during a tape SWAP, CA MIA requests the device group lock for the device before allowing the unit allocation request to continue. CA MIA then serializes the device group lock request with the other systems in the MIMplex as it would device lock requests for normal allocations.
CA MIA does not allow the unit allocation to continue until the device group lock becomes available to the local system; that is, no other systems in the MIMplex are currently using the device group lock. Once the lock is available to the local system, CA MIA allows the unit allocation request to continue to allocate the device. When the allocation is complete, CA MIA releases the device group lock for the device, notifies the other systems in the MIMplex that the lock is available, and plugs the allocated device on the other systems.
With device group lock serialization, only those allocations and SWAPs on external systems that are requesting the same device group locks as the local SWAP are delayed by the SWAP. Allocations and SWAPs on the external systems that do not involve the device group requested by the local SWAP continue. Conversely, only those allocations and SWAPs on external systems that are requesting the same device group locks as the local SWAP delay the local SWAP. If no allocations or SWAPs on external systems hold the device group lock requested by the local SWAP, the SWAP continues.
With device group lock serialization, local SWAPs do not delay HCD ACTIVATEs on external systems.
Note: Since z/OS carries out local serialization of the SWAP through the enqueue SYSIEFSD/DDRTPUR EXCL, allocations, SWAPs, and HCD ACTIVATES on the system local to the SWAP is delayed by the SWAP. Any local allocations, SWAPs, and HCD ACTIVATEs will delay the SWAP. This is true, regardless of the device groups associated with the local allocations and SWAPs.
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