<p>A computer system enabling quick and infallible equalization of the storage capacities of real logical area for dynamically providing a storage capacity to a virtual logical area. The computer system is characterized in that while dynamically allocating a storage area to a virtual logical area in response to an access from the host device, the system detects the time when the balance of the storage capacities of the logical areas is lost, and maintains the balance of the storage capacities by moving the storage area from logical areas to others.</p>
