Cache / disk system with command selection based on disk access time

摘要

A cache/disk subsystem responsive to commands from one or more host processors. The cache/disk subsystem includes a cache memory and a plurality of disk drives with a command queue being provided for each disk drive for storing commands awaiting execution with respect to that disk drive. These awaiting commands may include both host processor commands and trickle (write-back) commands. If less than a predetermined number of commands are awaiting execution in a command queue, selection of the next command is based on command priority. If more, then selection is based on the command having the fastest access time to its corresponding disk space taking both seek time and rotational latency into account. Exceptions are made for a high priority command or a command which remains unselected too long.