US Patent 7949827 Storage system and access count equalization method therefor

This invention aims to optimize an entire storage system by equalizing the access counts in appropriate units. When migrating data in pool volumes to equalize the data access counts, which data migration—data migration in units of pages or data migration in units of volumes—is most appropriate is judged based on the information stored in an access information table storing access information, which is the information about the access counts for the data stored in the disk drives and, based on the judgment, data is migrated in units of pages or volumes so that the data access counts are equalized among groups. The data migration is repeated until the data access counts are equalized among the groups.