A disk subsystem and a data restoration method with which the rise time when the disk subsystem is restored can be shortened.A disk subsystem and data restoration method whereby, when the power of the disk subsystem is shut off, the shared memory management table is saved to non-volatile memory together with the cache data and, when the power of the disk subsystem is restored, the shared memory management table is referenced and the duplex data is assigned by two non-volatile memories and restored to each of two shared memories.