To keep the CMEM and Control‑O shared variables and perform Sysplex-wide variable processing, CMEM and Control‑O require a list, a cache, and a lock structure.

Note: IOA allows you either to externally specify the space required for the structures by using the CFRM Administrative utility provided by IBM, or to let IOA internally calculate how much space will be required and then pass the calculated value to the IXLCONN service of MVS.

During space calculations and settings, note that different XES components use different units of allocation for calculation, For example, the STRSIZE parameter of the MVS macro IXLCONN specifies the size of the structure in units of 4 KB (4096 bytes) blocks while the INITSIZE(initsize) or SIZE(isize) used by the Administrative utility of the CFRM specifies the size of the structure in 1 KB (1024 bytes) blocks.

Therefore a structure allocated by the IXLCONN service that specifies STRSIZE=256 requires 1 MB (256 x 4 KB) of Coupling facility storage while the same structure space can be allocated with an INITSIZE of 1024 (1024 x 1 KB).