Patent ID: 7680983

Claim:
A storage system connected to a host computer, comprising: at least one interface connected to the host computer; at least one processor connected to the interface; at least one memory connected to the processor; and at least one disk drive which stores data requested by the host computer to be written, wherein the processor executes programs stored in the memory to implement a file system input/output processing unit receiving from the host computer a request to read data from a file and a request to write data in a file, and a block input/output processing unit reading and writing data from and to blocks in the disk drive, wherein the block input/output processing unit provides, to the file system input/output processing unit, storage areas of the disk drive as plural volumes including a first volume, a second volume, and a third volume, the first volume storing a file which is accessed by the host computer, the second volume storing a block write history which includes association between each of the blocks and a time when data is written in the block, the third volume storing a replication of data existing in the first volume at a specific time, wherein the block input/output processing unit refers to the block write history stored in the second volume to overwrite the replication data stored in the third volume with a replication of data existing in the first volume at a different time from the specific time, wherein the block write history stored in the second volume further includes information about which block is associated with which file; wherein, upon receiving file designation from the file system input/output processing unit, the block input/output processing unit extracts from the block write history stored in the second volume a part of the block write history relevant to blocks that are associated with the designated file, and wherein the block input/output processing unit sends the extracted part of the block write history to the file system input/output processing unit.