Patent ID: 7464223

Claim:
A storage system comprising: plural storage adaptors, each of which is provided with a cache memory that stores data according to a request from a host; an external storage coupled to said plural storage adapters, said external storage including at least one logical device that handles data and an external cache memory to one of said storage adaptors; and a monitoring computer coupled to said storage adapters, said monitoring computer configured to collect usage information relating to said cache memories of said plural storage adapters, wherein said at least one logical device of said external storage is selected based on said usage situation of said cache memory and is controlled by one of said plural storage adaptors, wherein said monitoring computer is further configured to acquire for each of said cache memories a first dirty data amount indicative of how much first dirty data is stored in said each of said cache memories and to select, based on said first dirty data amounts, a first storage adaptor having the smallest amount of dirty data, wherein said first storage adaptor serves to control said at least one logical device of said external storage.