MPC dynamics

With MPC dynamics support, if at least one WRITE and one READ subchannel path is allocated successfully, an MPC connection is activated. Additional paths (defined but not ONLINE) in an MPC group can later be dynamically added to the active group using the MVS™ command VARY device ONLINE. For example, if there is a need for an increase in capacity to allow for extra traffic over a channel, additional paths can be added to the active group without disruption. Similarly, paths can be deleted from the active group when no longer needed using the MVS command VARY device OFFLINE.

Note: By default, the last READ and last WRITE subchannel paths in an MPC group cannot be deleted. To be able to use VARY device OFFLINE to delete the last READ or last WRITE subchannel path in an MPC group, include LASTRW=ALLOW on the TRLE definition statement for the MPC connection. For details on the TRLE definition statement, see the z/OS Communications Server: SNA Resource Definition Reference.

If a path fails, it can be dynamically added back to the active group without disruption [automatically using the Event Notification Facility (ENF) channel recovery support or by issuing the MVS command VARY device ONLINE].

When an MPC connection is activated, if the minimum number of WRITE and READ subchannel paths cannot be allocated successfully, either because they are offline or no valid path exists to the connecting host, then activation is suspended until the minimum number becomes available. This is true unless the start option specification MPCACT=NOWAIT is in effect.