Patent ID: 7155593

Claim:
A data migration method in a virtualization system coupled to a plurality of storage subsystems which store data written by a host device, each of the plurality of storage subsystems presenting at least one storage volume configured with a plurality of physical storages as a storage resource to the virtualization system, the virtualization system presenting at least one of virtual volumes as a storage resource to the host device, the data migration method comprising: mapping a first storage volume to a first virtual volume classified as a first tier, the first storage volume being configured with a plurality of physical storages in a first storage subsystem; mapping a second storage volume to a second virtual volume classified as a second tier, the second storage volume being configured with a plurality of physical storages in a second storage subsystem; managing the first virtual volume and the second virtual volume together as a migration group; and in response to receiving a migration instruction for the migration group, migrating data in the first storage volume to a third storage volume and data in the second storage volume to a forth storage volume, the third and forth storage volumes being configured with a plurality of physical storages of third and forth storage subsystems, respectively, wherein a relationship of tier position between the third volume and the forth volume is based on a relationship of tier position between the first tier and the second tier.