A storage virtualization system is disclosed for performing data migration operations among the virtual LU (logical units) defined by the system. In one aspect of the present invention, the selection of a target virtual LU is based on a policy that makes a recommendation relating to the target virtual LU. The recommendation is based on the I/O activity of the physical devices which constitute the virtual LUs. In another aspect of the present invention, a replacement policy is recommended to replace a current policy. The replacement policy is based on the I/O activity of the physical devices which constitute the virtual LUs.