Patent ID: 7421547

Claim:
A storage system configured to communicate with an external device, that is an externally existing device, comprising: a plurality of storage units for storing data; a management storage area for storing a unit ID and a specific value corresponding to each storage unit; and a controller, wherein said controller (A) updates a specific value on said management storage area corresponding to a first unit ID of a certain storage unit, whenever receiving a formatting instruction specifying said first unit ID, and receives a command specifying a second unit ID from the external device, said second unit ID being identical with or different from said first unit ID, (B) when the command is a write command and data in said command is written to a certain storage unit corresponding to said second unit ID according to said command, acquires a specific value corresponding to said second unit ID from said management storage area, attaches said acquired specific value to the data in said command, and writes the data together with the attached specific value as a data group to said certain storage unit, and (C) when the command is a read command and a data group is read from a certain storage unit corresponding to said second unit ID according to said command, acquires a specific value corresponding to said second unit ID from said management storage area, compares said acquired specific value with a specific value attached to read data in said data group, sends said read data to the external device of said command if the specific values match, and does not send said read data to the external device of said command if the specific values do not match.