Patent ID: 8639899

Claim:
A storage apparatus providing a logical storage area for storing data to an external apparatus, comprising: a plurality of storage devices each providing a physical storage area for storing the data, the storage devices being different from each other in a device property including data input/output performance; a capacity virtualization part managing the physical storage areas of the storage devices as unit physical storage areas each having a predetermined storage capacity and managing the unit physical storage areas in association with a plurality of unit logical storage areas forming the logical storage area; a tier controller managing the plurality of unit physical storage areas by classifying the unit physical storage areas into a plurality of tiers, the unit physical storage areas provided by the storage devices having the different device properties; and a redundant data management part managing redundant unit storage areas which are a plurality of the unit physical storage areas storing the same data, wherein the tier controller classifies each of the unit physical storage areas into one of the tiers by use of a threshold of an access frequency from the external apparatus through the unit logical storage areas, the tier controller calculates as the access frequency an access frequency to each of the unit physical storage areas belonging to the tiers based on an access record from the external apparatus, and classifies the unit physical storage areas into the tiers by comparing the calculated access frequencies with the access frequency threshold, and when a piece of the data is migrated between the tiers, the redundant data management part determines if the unit physical storage areas classified into the tiers by the tier controller include the redundant unit storage areas, when determining that the tier of a destination of the data migration includes the redundant storage areas, the redundant data management part changes a mapping of the unit logical storage area to the unit physical storage area as a source of the data migration to the mapping to the unit physical storage area as the destination, and, when the migration destination and the migration source are in the same tier, the redundant data management part changes the mapping of the unit logical storage area to the unit physical storage area that is any of the redundant unit storage areas to the mapping to another redundant unit storage area in the same tier.