A multi-stage technique invalidates and replaces loadable physical volume block numbers stored in indirect blocks of a dual vbn virtual volume of a storage system to enable efficient image transfers andor fragmentation handling of the flexible vvol. The method of centring includes attaching the disk to the spindle with a stick-slip clamp. The extended electrode layer is folded back together with the insulating layer to a side opposite to the second substrate, to constitute an electrode taking-out portion.