Patent attributes
In the computer system where the plurality of host computers and the plurality of storage apparatuses are interconnected, in order to carry out the data migration between the storage apparatuses transparently to the host computers, the back end server provides the virtual disk to the host computers. From the host computers, at first, the virtual disk looks the same as the old storage subsystem. When migrating the data from the old storage subsystem to the new storage subsystem, at first, the back end server instructs the data migration unit to execute the data migration processing. Subsequently, the back end server switches the setting of the virtual disk, thereby causing the virtual disk to correspond to the new storage subsystem.