Storage controller and data management method

A storage system comprising a primary storage control device having a first logical volume and a secondary storage control device having a second logical volume capable of forming a copy pair with the first logical volume,

• said primary storage control device further 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, and
• said secondary storage control device further comprising:
• a second transfer differential bitmap table for managing positions of updates to the second logical volume due to remote copying;
• second snapshot management information for logically reconfiguring a data image of the second logical volume;
• a second pool region for storing differential data prior to updating said data image of the second logical volume as a result of remote copying data to the second logical volume;
• a second cache memory for temporarily storing the data;
• a second CPU for writing the data prior to updating to the first pool region when the second logical volume is updated as a result of remote copying and for updating section for updating the second snapshot management information with information for logically reconfiguring said data image for the second logical volume occurring at the time of the predetermined timing when the second logical volume is updated,
• wherein said first snapshot management information is selectively managed by either a first block area or a second block area which is smaller than the first block area,
• wherein the primary storage control device manages the first pool region and the second pool region,
• wherein the first pool region includes a plurality of first pool volumes and corresponds to at least one of a plurality of first logical volumes, and
• wherein the second pool region includes a plurality of second pool volumes and corresponds to at least one of a plurality of second logical volumes.