In most customer sites, if the coupling facility (CF) must be brought down for maintenance, a CF structure must be moved. If other CF-related planned outages must occur, the system (including all production jobs and system address spaces) is brought down. If the customer site does not want to bring their system activity to a halt, we recommend temporarily switching the interface between CMEM and Control‑M, meaning both CMEM and Control-M, to use the communication files. Assuming the IOACPRM PARM member is updated with the system IDs, system names, and the communication file names, this involves a simple change from SYSTLOGR=Y to SYSTLOGR=N and the recycling of CMEM and Control-M.

If CF system maintenance is attempted without switching over to the communication files, CMEM will not be able to write to the system logger and CMEM events will be lost. CMEM does not queue, save, and retry CMEM events in this case. Also, Control-M will not be able to read from the system logger and eventually the CMEM facility will be disabled.

The interface between CMEM and Control-M assumes a healthy and stable system logger environment. If this is not the case, the customer site should use the communication files instead of the system logger interface.