1. A storage system coupled to a host computer, comprising: a non-volatile medium that stores data; a disk cache that temporarily stores data stored in the non-volatile medium; a control unit that controls an input and an output of data to and from the non-volatile medium; and a memory unit that stores information used by the control unit, wherein: the control unit divides the disk cache into at least one of independent disk cache partitions; the memory unit stores first information that indicates states of respective memory areas in the disk cache, and second information that indicates states of respective memory areas in the disk cache used by the divided disk cache partitions; and the second information includes information that designates the first information corresponding to the respective memory areas in the disk cache.