| 摘要 |
PROBLEM TO BE SOLVED: To provide an external storage where an inexpensive magnetic tape drive device of low reliability can be mounted and which can reduce its cost by storing the same data as those of the external storage also in an internal hard disk, reading the data again out of a portable storage medium after writing them and then comparing these read data with the original data stored in the hard disk. SOLUTION: The data received from a higher order host 9 are written into a portable storage medium contained in a library device 1 via a controller part 6. The part 6 stores the received data in its internal hard disk 5 and manages its entry number. Then the part 6 mounts the portable storage medium on the device 1. When the writing of data is over, the portable storage medium is demounted and then mounted on another magnetic tape drive device 4 that is connected to another path to read again the data. These read data are compared with the original data stored in the disk 5. Thus, the reliability of data can be secured.
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