Provided are a storage apparatus and data management method with which the usage ratio of each of the storage tiers is determined beforehand for each virtual volume and data can be managed by being migrated between storage tiers within a range of predetermined usage ratios.A storage apparatus 5, comprising storage devices 30 of a plurality of types of varying performance; and a controller 31 which manages each of storage areas provided by the storage devices 30 of a plurality of types by means of storage tiers ST of a plurality of different types respectively, and which assigns the storage areas in page units to virtual volumes VVOL from any storage tier among the storage tiers ST of a plurality of types, the controller 31 managing usage ratios of the storage tiers ST of a plurality of types and assigning the storage areas in page units to the virtual volumes VVOL based on the usage ratio managed.