A subsystem builds a structure in one coupling facility. If that coupling facility should fail, the subsystem is notified. Most subsystems attempt to rebuild the structure in an another coupling facility. A subsystem running on any z/OS® system in the Parallel Sysplex® that attempts a rebuild will rebuild the structure from information kept in processor storage.

Recommendation: For maximum availability, set up at least two coupling facilities in your Parallel Sysplex, with global connectivity to the multiple z/OS images in a multiple-processor environment. One is not enough because a coupling facility could fail, or maintenance could require the temporary removal of a coupling facility from the Parallel Sysplex. Both coupling facilities should have enough processor power and storage resources to run as the only coupling facility, if necessary.

While it is possible to set a coupling facility up as an LPAR, this is not the ideal configuration. If you set the coupling facility up that way and the machine goes down, you lose both the coupling facility and the SMSVSAM server that was running in another LPAR. If there is only one coupling facility, this results in the loss of the lock structure as well as the SMSVSAM server. Any data sets it might have been accessing are now in lost locks throughout the Parallel Sysplex until the SMSVSAM image comes back up and does lost locks recovery.

Related reading: For information about non-RLS access to data sets that have lost locks, see Accessing data sets that have retained locks or lost locks.