You need to provide a structure size for each structure you define in the CFRM policy. There is no standard structure size for RACF®; you need to determine the structure size that is best for your environment. Among the factors that determine structure size are:

• The number of systems in the sysplex
• The number of local buffers
• The number of blocks in the data set the structure is for
• The system workload

The structure size you specify in the CFRM policy is the sum of the amount of storage needed by RACF and the amount of storage needed for coupling facility control information. To determine the amount of storage needed for coupling facility control information, see PR/SM™ Planning Guide for the formula, and use the following characteristics of RACF cache structures:

• The target directory-to-data ratio is 1/1.
• The adjunct assignment indicator is 0.
• The data area element characteristic is 4.
• The maximum data area size is 1.
• The maximum number of storage classes is 1.
• The maximum number of castout classes is 1.

When discussing structure sizes, there are four different structures sizes to consider: minimum, maximum, initial, and optimum.

• Minimum is the least amount of coupling facility storage RACF needs to successfully connect to the structure.
• Maximum is the amount of coupling facility storage it would take to contain the entire data set that the structure is for.
• Initial is an estimate of a size that allows you to do data sharing with acceptable performance.
• Optimum is the smallest structure size at which system performance is “good”. (If you are operating at a less than optimal structure size, an increase in the structure size significantly improves the I/O rate to the RACF database.)