Developing preference and exclusion lists

When determining which coupling facilities to include in the preference list and which structures to include in the exclusion list, consider various factors. For example,

If a structure has a backup structure containing the same information, you would want to place the backup structure in a different coupling facility. Specify each structure in the other's exclusion list and specify different preference lists for each structure.
If two structures with high activity reside in the same coupling facility, you would probably want to separate them for performance reasons. Specify each structure in the other's exclusion list and specify different preference lists for each structure.
If a structure requires a certain operational level (CFLEVEL) of coupling facility because of the function it provides (such as the structure alter function), you would need to include coupling facilities of only that CFLEVEL in or higher in the structure's preference list.
If a structure has been defined so that it can be rebuilt (due to coupling facility failure, structure failure, loss of coupling facility connectivity, or for planned coupling facility reconfiguration or maintenance activities), you must list more than one coupling facility in that structure's preference list to allow the structure to be rebuilt in a different coupling facility. The system will not allocate a structure in any coupling facility that is not listed in the structure's preference list.
If you intend to allow a structure to use storage-class memory, consider including in its preference list only those coupling facilities that are at CFLEVEL 19 or above which have storage-class memory configured.

You can specify when formatting your CFRM policy whether the order in which the coupling facilities are listed in the preference list is to be enforced with ENFORCEORDER (YES|NO). Specifying ENFORCEORDER(YES) prevents MVS™ from reordering the list when attempting to choose the coupling facility in which to allocate a structure. (See How MVS uses the lists.) When listing the coupling facilities, keep in mind that even though some connectivity requirements may have been specified by the application, the system will ignore them if ENFORCEORDER(YES) is specified. For example,

The CFLEVEL specification will not be honored. This might result in application connect failures if the structure cannot be allocated in a coupling facility of a high enough level.
The CONNECTIVITY=BESTGLOBAL request also is not honored. This parameter, by definition, specifies that the system is to use the coupling facility selection algorithm.

With ENFORCEORDER(YES), the amount of storage requested for a structure (with the INITSIZE and SIZE CFRM policy parameters) will be honored only to the extent of the available storage in the coupling facility. The system will not choose the next coupling facility in the preference list simply because the first coupling facility did not have the requested amount of storage available. If the system was able to allocate the structure with viable object counts in the first coupling facility in the preference list, then despite the degraded size of the structure, that is where it will be allocated.