CF cache structures must be defined to MVS and also in the SMS base configuration. CF cache structures provide a level of storage hierarchy between local memory and DASD cache. They are also used as a system buffer pool for VSAM RLS data when that data is modified on other systems. Each CF cache structure is contained in a single CF. You might have multiple CFs and multiple CF cache structures.

You use CFRM policy definitions to specify an initial and maximum size for each CF cache structure. DFSMS uses the initial structure size you specify in the policy each time it connects to a CF cache structure. If additional space is required, RLS manages the altering of the cache, up to the maximum size specified. Do not specify ALLOWAUTOALT(YES) for RLS cache structures, which would allow system-initiated alters, thus preventing RLS from being given control to manage the cache structure.

You can assign one or more CF cache structures to each cache set associated with a storage class. Having multiple cache sets allows you to provide different performance attributes for data sets with differing performance requirements. When more than one CF cache structure is assigned to a cache set, data sets are assigned to each CF cache structure in an effort to balance the load.