The storage system includes a first partition which is associated with a first processor and in which the first processor temporarily stores data relating to I/O requests processed by the first processor; and a second partition which is associated with a second processor and in which the second processor temporarily stores data relating to I/O requests processed by the second processor. Each processor independently controls the size of the first partition of the first cache memory and the size of the first partition of the second cache memory, and also independently controls the size of the second partition of the first cache memory and the size of the second partition of the second cache memory.