Control-O/CMEM supports only System-Managed Rebuild and System-Managed Duplexing Rebuild. The original coupling facility must be available for the system to be able make a copy using the System-Managed Rebuild or the Duplexing Rebuild method. The system maintains a hot copy of a Duplex structure in real time on another coupling facility after the Rebuild.

In System-Managed Duplexing Rebuild the Rebuild takes place immediately after the initial creation of the structures and enabling for smooth recovery. The failover of the structures to the alternate copy occurs without any disruption of work for the connectors that are on the non-failed systems.

User-Managed Rebuild and Duplexing Rebuild enables recreating a new copy of the structure on an alternate coupling facility without the availability of the original coupling facility. This is accomplished by making use of the data available to the connectors and requires the implementation of a synchronization protocol between the connectors. This Rebuild process takes place after the failure and causes an interruption to the normal work during the rebuild processing.

Control-O/CMEM does not support User-Managed Rebuild and Duplexing Rebuild, since the User-Managed Rebuild and Duplexing Rebuild require more complex support by the connectors (Control-O/CMEM Monitors), and provide less availability than the System-Managed Duplexing Rebuild.

To provide for smooth recovery and failover of the structures used by Control‑O/CMEM in case of a coupling facility failure, Control-O/CMEM structures must be defined as Duplex and not as Simplex.

Note: IOA Coupling Facility structures do not support the ALTER function.