| 摘要 |
The reduction of the volume capacity necessary to copy the snapshot can be achieved. When an operation volume is updated, the data before the update is saved in a difference storing volume, and the data of the two volumes, that is, the operation volume and the difference storing volume are combined to constitute the snapshot. In order to constitute the snapshot, the data necessary to constitute the snapshot is copied to the snapshot saving volume by using the block copy management table in which the data location in the operation volume and the difference storing volume is recorded, and another block copy management table for retaining the data location after the copy is saved in the volume. The saved snapshot can be referenced by accessing the snapshot saving volume, to which the data constituting the snapshot is copied, by using the snapshot read program.
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