To eliminate duplicated caching in a storage system with plural disk cache partitions, which are obtained by dividing a disk cache. A storage system includes non-volatile medium that stores data; a disk cache that temporarily stores data to be stored in the non-volatile medium; a control unit that controls input and output of data to and from the non-volatile medium; and a memory unit that stores information used by the control unit. The control unit divides the disk cache into at least one of independent disk cache partitions. The memory unit stores the first information that describes states of respective memory areas in the disk cache, and the second information that indicates states of respective memory areas in the disk cache used by the divided disk cache partitions. The second information includes information that identifies the first information corresponding to the respective memory areas in the disk cache.