Patent ID: 7668875

Claim:
A data storage device for storing, in a sequential storage medium that stores data through sequential accesses, data stored in a random storage medium that stores data through random accesses, comprising: history storing means storing, when data is stored in the sequential storage medium, storing history information on the stored data; and data re-storing means discriminating between valid data and invalid data that are stored in the sequential storage medium that is an arbitrary process target, and storing, at an arbitrary timing and on the basis of the discrimination result and the storing history information stored by the history storing means, the valid data in a sequential storage medium in use that is other than the process target sequential storage medium; wherein: the invalid data is data that exists before an update in cases in which data stored in the random storage medium is undated and the undated data is stored in the sequential storage medium, and valid data of the process target sequential storage medium that is stored in the sequential storage medium that is in use and that is other than the process target sequential storage medium is also handled as invalid data; and when the process target sequential storage medium has no more valid data, the data re-storing means handles the process target sequential storage medium as a blank medium.