Duplexing rebuild is a process by which a duplexed copy of a structure is created and maintained, so that in the event of a failure, a viable structure will remain available to the application. While the structure is duplexed, operations to the structure are maintained in a synchronized manner — with user-managed duplexing rebuild, through unique protocols designed by the subsystem, and with system-managed duplexing rebuild, through protocols established by z/OS®. For either method (user-managed or system-managed) of duplexing rebuild, the installation has the final word on whether it will allow a structure to be duplexed by controlling the setting of the DUPLEX keyword in the installation's active CFRM policy.

• User-managed duplexing rebuild is available only for cache structures. At the current time, it is used by DB2® for its group buffer pools. When an exploiter of duplexing rebuild supports both methods (user-managed and system-managed), the user-managed method will always take precedence over the system-managed method.
• System-managed duplexing rebuild applies to all structure types. Any application that provides support for system-managed processes can participate in either system-managed rebuild or system-managed duplexing rebuild. See Coupling facility structures for IBM products.