Storage system and processing migration method

A processing migration method in a storage system including a storage drive that physically stores data and a plurality of storage apparatuses each including a controller and providing a volume from and to which a host inputs and outputs data, the processing migration method comprising:

• by each of the storage apparatuses, generating access data and writing data into the storage drive at a time of write processing for writing data to the volume, and accessing data in the storage drive using the access data at a time of read processing for reading data from the volume;
• and
• in a case of migrating the volume together with the access data between the storage apparatuses,
• migrating one responsible for the write processing on the volume to a migration destination storage apparatus at a time of migration of the access data, and one responsible for the read processing on the volume being performed by a migration source storage apparatus using the access data, and
• migrating the one responsible for the read processing to the migration destination storage apparatus after the access data is available for the migration destination storage apparatus.