Patent ID: 7103731

Claim:
A method for managing data in storage units, comprising: maintaining storage pool information indicating an assignment of a plurality of storage units to a plurality of storage pools, wherein each pool is assigned zero or more storage units, wherein data associated with one storage pool is stored in a physical medium of a storage unit assigned to the storage pool, wherein the storage pool information for each pool indicates a threshold and target storage pool, and wherein the target storage pool is capable of being different from the storage pool; selecting one storage unit associated with a source storage pool; determining the threshold from the storage pool information for the source storage pool; determining whether the physical medium of the selected storage unit satisfies the determined threshold wherein the physical medium of the selected storage unit satisfies the determined threshold if an amount of active data stored in the physical medium of the selected storage unit is less than the threshold; if the physical medium of the selected storage unit satisfies the determined threshold, then selecting a target storage unit in the target storage pool if the storage pool information for the source storage pool indicates a target storage pool different from the source storage pool; and copying data from the physical medium of the selected storage unit to a physical medium of the selected target storage unit.