Using cache structures

CF cache structures are defined to z/OS® using coupling facility resource management (CFRM) policies, which determine how and where the structures are allocated. You associate these cache structures with a cache set name in the base configuration. The cache set name is also specified in a storage class definition. When a storage class associated with a data set contains a cache set name, the data set becomes eligible for VSAM record-level sharing and can be placed in a CF cache structure associated with the cache set. The system selects the best cache structure within the cache set defined for the storage class.

CF cache structures must have the same system connectivity as any storage groups that might be assigned to those cache structures. For example, if Storage Class 1 maps to cache set CS1, then the CF structures in CS1 must have the same system connectivity as the storage groups with which Storage Class 1 is associated. Connectivity of CF cache structures to all systems in the Parallel Sysplex® simplifies managing and changing the configuration.

Recommendation: In a JES3 environment, be careful to define cache set names only in those SMS storage classes that are used by data sets opened for VSAM RLS processing. When you define a cache set name in a storage class, any job accessing a data set associated with that storage class is scheduled on a VSAM RLS-capable system (one where the SMSVSAM address space has been successfully initialized). If all storage classes have cache set names defined for them, then all jobs accessing SMS-managed data sets are scheduled to VSAM-RLS-capable systems. This could cause a workload imbalance between those systems and down-level systems.

See Defining CF cache structures for more information on defining CF cache structures. See Defining the base configuration for more information on defining the base configuration.