Coupling facility log streams

If you use a coupling facility, the most suitable environment is provided by two or more non-volatile coupling facilities that are failure-independent from any of the exploiting MVS™ images, using dedicated processor resources.

If one coupling facility fails, or requires maintenance, in such an environment, the system logger can rebuild its data in another coupling facility and continue. CICS® systems that are running are minimally affected.

To define a higher availability Sysplex, review z/OS MVS Setting Up a Sysplex.

If possible, do not run with a single coupling facility because its failure can cause the MVS system logger, and any other users of the coupling facility, to suspend normal operation until access to the coupling facility is restored. CICS is effectively unusable in such a situation.

Unless you specify that the system logger is to use staging data sets, the recovery of log stream data depends on the MVS images remaining active so that the system loggers can use copies of log records held in storage to repopulate the coupling facility when it is again available. If you must run with a single coupling facility, specify DUPLEXMODE(UNCOND) to force the use of staging data sets.