Storage controller and data management method

A primary storage control device control method comprising the steps of

• accepting host accesses to the primary storage control device having a first logical volume;
• managing positions of updates to the first logical volume due to host accesses using a first differential bitmap table;
• temporarily storing differential data;
• writing, via a first CPU differential data to a first pool region prior to updating said data image of the first logical volume from the predetermined timing onwards as a result of a host access;
• updating, via the first CPU, first snapshot management information for logically reconfiguring a data image of the first logical volume with information for logically reconfiguring said data image for the first logical volume for the point in time of the predetermined timing when the first logical volume is updated at the predetermined timing onwards;
• merging bit information of the first differential bitmap table with a first transfer differential bitmap table for managing whether or not update data for the first logical volume possessed by the primary storage control device is remote copied to a second logical volume possessed by a secondary storage control device;
• discerning, via the first CPU, 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 a discerned party and remote copying the data to the second logical volume;
• managing positions of updates to the second logical volume due to remote copying using a second transfer differential bitmap table;
• writing differential data to a second pool region prior to updating said data image of the second logical volume as a result of remote copying data to the second logical volume;
• updating second snapshot management information for logically reconfiguring a data image of the second logical volume with information for logically reconfiguring said data image for the second logical volume for the point in time of the predetermined timing when the second logical volume is updated;
• selectively managing said first snapshot management information by either a first block area or a second block area which is smaller than the first block area;
• and
• managing a first pool region and a 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.