The decision to enable a particular structure for system-managed duplexing rebuild is done at the installation level, through the DUPLEX keyword in the CFRM policy. Even in a hardware-software configuration that is fully supportive of system-managed duplexing rebuild, it may not be to the installation's benefit to exploit the function for certain of its structures. The installation must consider, on a structure by structure basis, whether the availability benefits to be gained from system-managed duplexing rebuild's robust failure recovery capability for a given structure outweigh the additional costs associated with system-managed duplexing for that structure. The availability benefit depends on considerations such as whether or not the structure exploiter currently supports rebuild, whether that rebuild process works in all failure scenarios, and how long that rebuild process generally takes, among others, compared to the rapid failover recovery capability that duplexing provides. The costs depend on considerations such as the hardware configuration cost (possible additional coupling facility processor and CF link capacity requirements), software configuration cost (possible upgrades to installed software levels), and the coupling efficiency cost of duplexing the structure given its expected duplexing workload.

Based on these considerations, an installation might well make a conscious decision to duplex only a subset of the structures that support duplexing, given their installation's unique workload, considerations, and tradeoffs. For example, some installations might choose to duplex all structures that do not provide any user-managed rebuild recovery mechanism, but leave all structures that do provide a user-managed recovery capability unduplexed. Other installations might also want to duplex some of the structures that do have a user-managed rebuild capability, because duplexing provides a faster or more robust recovery mechanism than rebuild does under some circumstances. Other installations might choose to duplex all eligible structures except for a few intensively-used datasharing and duplexing intensive structures for which the coupling efficiency cost is not justified in terms of the availability advantage that duplexing provides. And of course, some installations might choose to duplex all eligible structures.