Understanding the coupling facility level (CFLEVEL)
The level (CFLEVEL) of the coupling facility control code (CFCC) that is loaded into the coupling facility LPAR determines what functions are available for exploiting applications. Different levels provide new functions and enhancements that an application might require for its operation. As more functions are added to the CFCC, it might be necessary to allocate additional storage to a coupling facility structure. Similarly, as new functions are added, the coupling facility itself may require additional storage. In any configuration, the amount of fixed storage required for the coupling facility is based on configuration-dependent factors. This “fixed overhead” may be associated with the coupling facility's code areas or fixed controls and must be considered in addition to the storage needed for structure allocation.
IBM® recommends that you review the sizes of all your coupling facility structures using the CF Structure Sizer (CFSizer) tool before migrating to a coupling facility at a higher CFLEVEL.
After reviewing your coupling facility structures with CF Structure Sizer (CFSizer), modify your CFRM policy INITSIZE and SIZE values appropriately for the structures that changed. Then activate the modified CFRM policy before bringing the coupling facility at the new CFLEVEL into active use.
In general, IBM recommends that coupling facility structures be sized generously, erring on the side of too-large rather than too-small, because sizing structures too-small is a major factor in many different kinds of structure-related problems and outages. Be careful to re-plan so that:
See also Requesting structure size.
PR/SM Planning Guide provides information about the functions available with each CFLEVEL of a coupling facility, model-dependent limits, and other characteristics such as performance, storage allocation, and operations.
Base coupling facility function is available with coupling facility control code (CFCC) level 0 (CFLEVEL=0). Additional function and enhancements are provided by follow-on CFLEVEL versions. For the most accurate list of CFLEVEL functions with associated hardware and software corequisites, see Coupling Facility Level (CFLEVEL) Considerations.
An application might require that its structure be allocated in a coupling facility at a minimum coupling facility level. Or, an application might have a requirement for a particular CFLEVEL, but if a coupling facility of that level is not available, might allow its connectors to connect and run, bypassing the architected function provided by the higher CFLEVEL that was unavailable. To ensure that the structure allocation is successful, you must provide a preference list containing coupling facilities that meet or exceed the minimum level in your CFRM policy.
CFLEVEL and operating system level coexistence provides a summary of these functions and some exploiting products.