Patent ID: 7111134

Claim:
A storage controller for exchanging user data between a host system and a data storage unit comprising: at least one microprocessor; a local memory for a control program and for in-memory management information and not for the user data; and a cache memory for the user data, the cache memory storing therein in-cache management information, the in-memory management information being representative of the in-cache management information, the in-memory management information and the in-cache management information each being information relating to user data that is stored in the cache memory, an access time between the microprocessor and the local memory to perform an access operation being lower than an access time between the microprocessor and the cache memory for the same access operation, the local memory and the cache memory storing management information that is used only by the at least one microprocessor, the local memory and the cache memory exclusive of management information that is used by any microprocessor other than the at least one microprocessor, the control program configured to operate the microprocessor to process a read request by performing steps of: accessing the local memory to access the in-memory management information; based on the in-memory management information, determining whether read-out data associated with the read request is stored in the cache memory; if the read-out data is stored in the cache memory, then accessing the cache memory to access the read-out data; if the read-out data is not stored in the cache memory, then: accessing the data storage unit to access the read-out data; storing the read-out data in the cache memory; and updating the in-memory management information and the in-cache management information to indicate an update of the cache memory.