Abstract: A disk volume access controlling method includes the steps of setting a threshold number of times of accesses from a computer to a predetermined disk volume per time unit, acquiring a number of times of accesses to the predetermined disk volume per time unit, seeking whether or not the number of times of accesses acquired exceeds the threshold number of times, creating a mirror volume for the predetermined disk volume in case that the number of times of accesses acquired exceeds the threshold number of times, and changing an access pass between the computer and the predetermined disk volume to another access pass between the computer and the newly created mirror volume. It then becomes possible to distribute accesses to a certain disk volume, and further to make the accesses to a plurality of volumes even.