1. A disk array apparatus comprising: a plurality of I/O processing controllers for controlling an I/O processing between the I/O processing controller and an upper apparatus; and a storage apparatus storing data obtained according to I/O processings conduced in the plurality of I/O processing controllers, wherein each of the plurality of I/O processing controllers includes: a processor for performing an I/O processing; and a cache memory temporarily storing data obtained according to the I/O processing at the processor; the cache memory is logically divided to a plurality of memory area; and the storage apparatus includes a plurality of logical units, and the divided memory areas are allocated to respective logical units, when a failure occurs at a part of the cache memory, the processor performs: identification of an address of the cache memory where the failure has occurred and closes a first memory area of the identified address; determination about an access state from the upper apparatus to reallocate the logical unit that has been allocated to the first memory area to a second memory area of the cache memory where the failure has occurred based on the result of the determination; and continuation of an I/O processing from the upper apparatus using the reallocated second memory area.