When DUPLEX(ENABLED) is specified for a structure in the active CFRM policy, the system will attempt to start a duplexing rebuild for a structure that is not currently duplexed when certain triggering events occur. Such duplexing triggers are shown in the following examples:

• The structure becomes allocated with at least one active connector.
• The CFRM policy changes to DUPLEX(ENABLED) for an allocated structure with at least one active connector.
• A new coupling facility resource becomes available.
• The last connector that did not support duplexing rebuild (ALLOWDUPREBLD=NO) disconnects or is forced from the structure.

The system will not attempt to start a duplexing rebuild for the structure under the following conditions:

• The new structure in duplexing rebuild could not be allocated with the same connectivity as the old structure.
• Stop processing completes, and IGNOREDUPLEX=YES was specified on the IXLREBLD STOPDUPLEX request.

The system might be unable to duplex a structure again after an operator-initiated stop of the duplexing rebuild process.

• When an operator initiates a stop of the duplexing rebuild, the system will stop it as requested. There might be a delay before reduplexing when only two coupling facilities are available for duplexing the structure. Reduplexing will occur immediately in configurations with three or more coupling facilities available for duplexing the structure. When reduplexing the structure for this trigger, the system ensures that the structure is not duplexed back into the same coupling facility from which a duplex instance of the structure was just deallocated. Note, however, that if the duplexing rebuild fails or is stopped again, the coupling facility for which the duplexing was stopped may be selected for the next duplexing attempt.

MVS™ will stop the duplexing rebuild for the structure under the following conditions:

• The CFRM policy changes to DUPLEX(DISABLED).
• A coupling facility containing one of the structures is removed from the structure's preference list.