Additional CPU requirements are lowest with cache areas in main memory.
Hit rates > 90% are generally achieved with AutoDAB. A small prefetching factor is set for accesses which are predominantly non-sequential (random) while a larger one is set for predominantly sequential accesses. The CPU utilization for the read/write cache includes the requirement for save I/Os to the disk.
Effect of the FORCE-OUT operand
The FORCE-OUT operand of the /START-DAB-CACHING command can be used to control saving of cache data to disk. FORCE-OUT=*AT-LOW-FILLING causes saving to be started whenever 25% of the cache area are filled with write data not yet saved; FORCE-OUT=*AT-HIGH-FILLING triggers saving at an occupancy of 75%. FORCE-OUT=*AT-LOW-FILLING is always recommended. FORCE-OUT=*NO is recommended for resident buffering, since this specification suppresses I/Os for saving data to disk, which is superfluous with this caching technique.
With automatic caching, any incorrect setting of this operand is corrected (see also section“Automatic caching (AutoDAB)”).