Patent ID: 7752409

Claim:
A computer system comprising a plurality of storage systems for managing a storage extent of an external storage apparatus connected to a network as a volume, and a host computer connected to said network; wherein a source storage system among said plurality of storage systems comprises: a guarantee code creation unit for creating a guarantee code corresponding to read or write access-target data; a processor for controlling the writing of said created guarantee code in said external storage apparatus or the reading of said guarantee code stored in said external storage apparatus; a confirmation unit for confirming the concordance of a guarantee code created from said access-target data and a guarantee code read from said external storage apparatus as a guarantee code corresponding to said access-target data; and a management migration unit for migrating data stored in said external storage apparatus and management information including volume management information of a migration-target external volume and key information which includes a volume key of an external volume, each information being related to said guarantee code; wherein a target storage system comprises a management unit for managing said management information migrated from said source as target management information.