Patent ID: 8572319

Claim:
A storage system composed of a storage device coupled to one or more upper level devices and a management terminal; the storage device comprising a plurality of memory device units assigned to different tiers respectively, a data location management unit configured to manage location of data in the respective tiers and migration of data among the tiers, and a migration amount calculation unit configured to calculate a data storage time in the respective tiers and a data migration amount when data are migrated among the tiers; the management terminal comprising an input unit, an output unit, and a cost calculation unit; wherein based on a result calculated using the migration amount calculation unit, the cost calculation unit is configured to calculate: (1) a stored cost for storing data in a tier; (2) a first migration cost for migrating data to an upper tier level; and (3) a second migration cost for migrating data to a lower tier level; and at least one of the calculated costs (1) through (3) is displayed on the output unit of the management terminal; wherein the second migration cost is calculated using at least a migration data amount, a migration destination tier level and a migration source tier level; and wherein the calculation is performed so that an amount of increase in the second migration cost does not exceed an amount of decrease in the stored cost.