Patent ID: 7512753

Claim:
A disk array control apparatus comprising: a control element constructed and arranged so that the control element generates multiple I/O processes for processing I/O requests to a disk array, the multiple I/O processes including first tasks with a first priority and second tasks with a second priority that is lower than the first priority, wherein an upper limit of a number of the first tasks is a first number, and wherein the first tasks and the second tasks are each I/O processes to said disk array; a first element constructed and arranged so that the first element calculates a cache hit ratio at a disk cache memory; and a second element constructed and arranged so that the second element executes the first tasks until the number of the first tasks being executed reaches the first number, and executes the second tasks and the first tasks when the number of the first tasks reaches the first number, except that the second element executes only the first tasks when the calculated cache hit ratio is above a prescribed value even if the number of first tasks reaches the first number.