In one embodiment, a storage system for storage management in a tiered storage environment comprises a plurality of storage volumes in a pool which are divided into a plurality of tiers having different tier levels, the tiers being organized according to a tier configuration rule, the plurality of storage volumes provided by a plurality of physical storage devices in the storage system; and a controller controlling the plurality of physical storage devices, the controller including a processor and a memory. The controller changes tier configurations of the tiers of storage volumes when the tier configuration rule is changed, the tier configurations including the tier levels. The controller allocates the pool to a plurality of virtual volumes based on a change of tier levels against the physical storage devices which occurs when the pool does not meet the tier configuration rule that was in effect.