Patent ID: 8209498

Claim:
A computer system comprising: a first computer; and a second computer, wherein: the first computer includes a first storage area for storing files transmitted/received to/from a host computer; the second computer includes a second storage area for storing files migrated from the first computer; the first computer migrates first and second files stored in the first storage area, to the second computer, according to the access state from the host computer, and provides first and second file identifiers corresponding to the first and second files, respectively; the second computer receives and stores the migrated first and second files in the second storage area; the second computer determines whether the migrated first and second files are identical to each other, and when determining that the migrated first and second files are identical to each other, the second computer generates duplicate file information indicating that the first and second files are identical to each other; the second computer transmits the generated duplicate file information to the first computer; the first computer manages the first file identifier associated with the second file identifier, based on the duplicate file information; when receiving a read request to the second file from the host computer, the first computer transmits an instruction asking the second computer to transfer the second file from the second computer; the second computer transmits the second file to the first computer; the first computer stores the received second file as a file corresponding to the second file identifier into the first storage area, and transmits the second file to the host computer; and when receiving a read request to the first file from the host computer, the first computer determines that the second file identical to the first file is stored in the first storage area, based on the duplicate file information and on the first and second file identifiers, and responds to the host computer by using the second file.