RACF Help

RACF uses the Coupling Facility to improve performance by using a cache structure to keep frequently used information, located in the RACF database, quickly accessible. You need one cache structure for each data set specified in your data set name table (ICHRDSNT). For example, if you have one primary data set and one backup data set, you need to define two cache structures. The RACF backup structure only needs about 20% of the data capacity of the primary structure.

At a minimum, the RACF primary structure must be large enough to accommodate the data written from the instorage I/O buffers. Additional performance benefits may be gained by increasing the size of the structure to permit RACF to cache frequently-referenced profiles. Caching infrequently used profiles does not improve performance. The amount of CF storage needed to cache frequently-used profiles will vary from installation to installation. It should not exceed the size of the data set containing the RACF database, as this simply wastes CF storage.

Attention: RACF does not support the ALTER function of coupling facility structures. Therefore, do not specify the INITSIZE operand in the structure statement of the CFRM policy. If you do, the size of the structure is limited to the INITSIZE value instead of the SIZE value. If the INITSIZE value is less than the SIZE value, RACF issues an informational message IRRX012I. If this message is followed by IRRX013A, the structure size does not meet RACF's minimum requirements, and the system enters read-only mode.

 

Max # Instorage Local Buffers

The number of local ECSA resident buffers that the installation defines for each data set that comprises the database. The maximum number of local buffers is 255. IBM recommends that you define the maximum 255 buffers.

# Additional Buffers

The additional number of 4K buffers to be contained in the structure to improve caching performance. Specify for this value the estimated number of profiles in frequent use in the RACF database. Calculate this input as follows:

1. Determine the number of cylinders occupied by the RACF database dataset.
2. Determine the percentage of the dataset actually in use, from the output of IRRUT200.
3. The number of 4K blocks in use is
   
   (total cylinders) * (% cylinders used) *
   (15 tracks / cylinder) * (12 4K blocks / track)
   
   (for 3390 geometry)
4. Enter (number of 4K blocks in use) * (30%)
   
   where 30% is an initial estimate of the typical percentage of profiles in frequent use. If caching performance is not satisfactory, gradually increase this percentage until no further performance improvement is observed.

# MVS Images

Number of systems in the RACF data sharing group