Patent ID: 7058692

Claim:
A first computer system comprising: a first accessing unit coupled to a first disk unit storing data in a first format; a second accessing unit coupled to a second disk unit storing data in a second format, wherein the second format is different from the first format; a CPU for issuing a first type access request according to the first format; an interface configured to receive a second type access request according to the second format from a second computer system; a processor configured to receive the first type access request from said CPU and the second type access request from said second computer system via said interface; a disk cache configured to store data accessed from one of said CPU or said second computer system previously; first information on data locations in said second disk unit, wherein said first information includes location information of data stored in said second disk unit according to the second format and corresponding location information according to the first format; and second information indicating whether data stored in said second disk unit is stored in said disk cache or not, wherein said second information includes data location information of data stored in said second disk unit according to the second format and an information indicating whether data stored in the corresponding location in said second disk unit is stored in said disk cache or not; wherein said processor is configured to receive the first type access request from said CPU, control said second accessing unit to write the target data of said first type access request to said second disk unit by referring to said first information, store said target data in said disk cache, and update said second information; wherein when said processor receives the second type access request to read said target data from said second computer system via said interface, said processor judges whether said target data is stored in said disk cache based on said second information; and wherein if said target data is stored in said disk cache, said processor transmits said target data stored in said disk cache to said second computer system via said interface.