For each structure, RACF® needs 4K of coupling facility storage for each local buffer. For example, if you have requested 255 local buffers in ICHRDSNT, RACF needs 255 × 4K = 1020K of coupling facility storage for the primary structure. You need to add to this value the amount of storage needed for coupling facility control information. The minimum structure size of the backup data set is 20% of the minimum structure size of the primary. (This is because the number of local buffers for a backup data set is 20% of the number specified for the primary data set.) If the number of local buffers specified varies from one system to another, you must use the largest value specified. The minimum establishes a lower bound, and your structure size should be larger.