An embodiment of this invention divides a cache memory of a storage system into a plurality of partitions and information in one or more of the partitions is composed of data different from user data and including control information. The storage system dynamically swaps data between an LU storing control information and a cache partition. Through this configuration, in a storage system having an upper limit in the capacity of the cache memory, a large amount of control information can be used while access performance to control information is kept.