Patent ID: 7694087

Claim:
A duplicate data storing system of a storage device for storing original data of a copy source in a duplicate data storage area in accordance with an update of the original data, the system comprising: a real data storage area which stores data of a copy source, a copy of which is to be written as duplicate data to a duplicate data storage area which is virtually built within the storage device; a data-storage area determining device which determines a next storage area to be used for storing said duplicate data in a contiguous arrangement in the real data storage area; and a data-storage area managing device which manages where, in the real data storage area, the duplicate data of the duplicate data storage area is stored; a held-data managing device which manages a use state of the real data storage area; and a real data storage area expanding device which increases a storage capacity of the real data storage area, wherein a plurality of duplicate data storage areas share the real data storage area, wherein a storage capacity of the real data storage area which is physically secured in response to a snapshot command to store said data in the real data storage area corresponds to an amount of data of said copy source which is to be updated among original data of said copy source, and wherein the held-data managing device comprises: a table which indicates the presence of data by each memory unit through dividing the storage area of the real data storage area into memory units; a table which indicates the presence of data by each memory unit group in which a plurality of the memory units are put together; and a table with a plurality of hierarchies in which a plurality of the memory unit groups are put together to indicate the presence of data by each of the hierarchies.