Storage migration method and storage system

A storage system comprising:

• a plurality of storage controllers each including a processor and a memory;
• and
• a plurality of storage media configured to store data, the storage media each being managed by a corresponding one of the storage controllers,
• wherein each of the plurality of storage controllers requests data access and transmits and receives data with respect to a host computer,
• a plurality of the processors of the storage controllers process data input or output to the storage media by the host computer,
• a plurality of the memories of the storage controllers hold control information referred to by the processors to access the data stored in the storage media,
• a storage migration control apparatus is connected to the plurality of storage controllers,
• the storage migration control apparatus transmits a transfer instruction for the control information to a migration source storage controller among the plurality of storage controllers and transmits, to a migration destination storage controller different from the migration source storage controller among the plurality of storage controllers, the migration instruction for the control information and the control information on the migration source storage controller,
• a processor of the migration source storage controller transmits, on a basis of the transfer instruction, the control information to the storage migration control apparatus, and
• a processor of the migration destination storage controller determines whether a storage medium managed by the migration source storage controller has been relocated to the migration destination storage controller on a basis of the control information received from the storage migration control apparatus.