a storage device including a control part which performs control by extracting a life tag specifying a retention term during which the data is to be retained in the second volume having the quicker access time than the first volume , the control part managing the retention term of the corresponding data as specified by the life tag , and an elapsed term which has elapsed since the corresponding data was stored . a storage part manages update segment control information , and when the elapsed term of certain data exceeds the retention term of the certain data , the storage part nullifies the certain data in the second volume .