A storage apparatus and a storage method for decreasing the number of storage devices shared by a plurality of servers for reduced size and power consumption and for updating storage contents by preventing services from being degraded. A first virtual volume includes a plurality of storage devices and saves the same data in part or all of the storage devices. A virtualization engine detaches a storage device from the first virtual volume and generates a second virtual volume from the detached storage device. The virtualization engine further detaches a storage device from the first virtual volume and moves the detached storage device to the second virtual volume. The virtualization engine writes the difference between data saved in the first and second virtual volumes to the moved storage device.