When XRC suspends a storage control session on a storage control that does not support hardware bitmaps, the storage control continues to accumulate changes in its cache storage. At the end of the TIMEOUT duration, the storage control ends the storage control session. When you restart the XRC session with an XSTART command, the system data mover drains the storage control cache and accumulates the updates in a software bitmap. When you issue an XADDPAIR command, the software uses the software bitmap to resynchronize the volumes in the XRC session.
A suspended storage control session that experiences a lot of update activity places a greater demand on existing cache resources. This suspended session has an increased potential to significantly affect primary system performance. The storage control may cancel storage control sessions as a result.
If you do not issue the XSTART command before the timeout expires, the storage control ends the XRC session. You can monitor the current timeout for a storage control by issuing an "F ANTAS000,SCDATA" command. If the timeout is close to expiration, follow the procedure that is described in Examples: changing TIMEOUT intervals for suspended sessions to avoid having to recopy the volumes on the storage control.
If a suspended XRC session requires significant cache resources, other applications that are accessing the same storage control can encounter IEA482I, IEF196I, or ADR348E messages. You may choose to cancel the jobs that generate the messages, then rerun them after you have restarted the XRC session. Be aware that DFSMSdss concurrent copy sessions and suspended XRC sessions both use cache resources. The potential exists to overrun these resources, resulting in IEA482I, IEF196I, or ADR348E messages.
During any planned outage, primary systems that issue RESERVE commands to the utility volume will enter into a long-busy condition. Either a storage control report or the "F ANTAS000,SCDATA" command can identify the utility volumes in a suspended storage control session.
For additional information about an SCDATA operation, refer to SCDATA operation (XRC, CC).