| 摘要 |
Data can be recovered at the point in time when the consistency is provided, without increasing a load on the host. The control program 118 updates the snapshot generation at the point in time when the snapshot is taken for each occurrence of the point in time when the snapshot is taken. In cases where new data are written into PVOL 1 from the point in time when the snapshot has been taken until the next point in time when the snapshot is taken, the old data are saved by the CoW in DVOL 1 and new data are written into PVOL 1. Each time new data are written into PVOL 1, the update differential data, which are the copy of this data, are prepared and written into DVOL 1. The opportunity of providing the consistency of PVOL 1, which occurs independently of the operations of the user of the host computer 20, is taken and the update differential generation, which is the generation of update differential data at each point in time where the update differential data has been set, is updated each time the opportunity is taken. The recovery of PVOL 1 is conducted based on the managed update differential generation and snapshot generation.
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