Patent ID: 8478729

Claim:
A computer system, comprising: a processor; a first storage system including a first plurality of storage devices configuring primary logical units and a first controller controlling read/write accesses from a first host computer to the primary logical units; and a second storage system including a second plurality of storage devices configuring secondary logical units corresponding to the primary logical units and a second controller storing data received from the first storage system to the secondary logical units; wherein the first controller is configured: to compare a first data stored in a first reference location in the primary logical units to a second data stored in a second reference location in the primary logical units, and to detect if the first data is the same as the second data, and when the first data is the same as the second data, the first controller is configured: to release a storage area storing the second data from the primary logical units, and to update a second metadata of the second data to change reference location information from the second reference location to the first reference location, and wherein the first controller detects overlap of a first file stored in the first reference location in the first logical unit of the primary logical units and a second file stored in the second reference location in the second logical unit of the primary logical units, in which a reliability of the first logical unit is higher than the reliability of the second logical unit, wherein the first controller updates a second metadata of the second data to change reference location information from the second reference location to the first reference location, wherein the first controller sends the first file and the metadata file to the second storage system, and wherein when the first host computer updates an original file stored in the primary logical units by using a different filename as a new file, the first controller detects overlap data between the original file and the new file, creates a difference file based on the new file, releases a storage area of the original file from the primary logical units and writes the difference file to the storage area, wherein the first controller sends the difference file to the second storage system, wherein the first controller configured to create a metadata file consolidating a first metadata of the first data and the updated second metadata of the second data, and send the created metadata file and the first data to the second storage system without sending the second data to the second storage system.