Patent ID: 8266401

Claim:
A primary storage control device having a first logical volume, comprising: a first differential bitmap table for managing positions of updates to the first logical volume due to host accesses; first snapshot management information for logically reconfiguring a data image of the first logical volume; a first pool region for storing differential data prior to updating said data image of the first logical volume as a result of a host access; a first cache memory for temporarily storing the data; a first CPU for writing the data prior to updating to the first pool region when the first logical volume is updated at a predetermined timing onwards and for updating the first snapshot management information with information for logically reconfiguring said data image for the first logical volume occurring at the time of the predetermined timing when the first logical volume is updated at the predetermined timing onwards; a first transfer differential bitmap table for managing whether or not update data of the first logical volume has been remote copied to the second logical volume; a transfer bitmap table update section for updating the first transfer differential bitmap table by merging bit information of the first differential bitmap table with the first transfer differential bitmap table; and wherein the first CPU discerns whether each data constituting said data image for the first logical volume at the point in time of the predetermined timing is in the first logical volume or the first pool region based on the updated first transfer differential bitmap table, and acquiring data from the discerned party and transmitting the data to the second logical volume.