Storage system and control method thereof

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 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 data prior to updating constituted by data prior to updating as a result of a host access that is data written to the first logical volume;
• a first writing section for writing the data prior to updating to the first pool region when the first logical volume is updated at a predetermined timing onwards;
• a first snapshot updating section for updating the first snapshot management information with information for logically reconfiguring a data image for the first logical volume occurring at the time of the predetermined time 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
• a remote copy section for discerning whether each data constituting a 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 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 data prior to updating constituted by data prior to updating as a result of remote copying that is data written to the second logical volume;
• a second writing section 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
• a second snapshot updating section for updating the second snapshot management information with information for logically reconfiguring a data image for the second logical volume occurring at the time of the predetermined time when the second logical volume is updated.