| 摘要 |
PROBLEM TO BE SOLVED: To make the copy data quantity reducible in spite of being of a relatively small memory capacity in comparison with the case where a bitmap format is singly used, by using the bitmap format and a list format differently to store snapshot differential information. SOLUTION: The snapshot differential information is stored in a list format differential information table just after mirror separation. In the case the list format differential information table is full (S9) and also, an entry can not be newly added (S10), that is, while a differential information table area for storing the list format differential information table can not be expanded, the list format differential information table is converted into a bitmap format differential information table (S12), and after that, snapshot differential information is stored in the bitmap format differential information table.
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