A change in the DUPLEX keyword from DISABLED to either ALLOWED or ENABLED, or vice versa, becomes effective immediately. However, the effect of the change differs between user-managed and system-managed duplexing rebuild if other changes that become pending are also made to the policy at the same time. For user-managed duplexing rebuild, the allocation or deallocation of the duplexed structure will cause all pending policy changes to go into effect. For system-managed duplexing rebuild, the process cannot be started or stopped when policy changes are pending. If one or more policy attributes are changed in addition to the DUPLEX attribute, the system will be prevented from initiating duplexing rebuild because of the other pending policy changes.