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When Restore is performed, data copy from RV to MV starts to reflect the content of RV at the
beginning of Restore to MV. When Restore(update) is executed, any update to MV after Restore is
also reflected to RV.
After Restore is started, the difference between MV and RV gradually decreases, and eventually the
content of RV at the beginning of Restore is completely reflected to MV (The difference is zero). The
state from the beginning of Restore to the content of RV at the beginning of Restore is completely
reflected to MV is called the "Restore execution". The state where the difference between MV and
RV is zero is called the state synchronized by Restore, or simply the "synchronous state". Restore
execution and the state synchronized by Restore are collectively called the Restore state.
When Restore(protect) is executed, the updated data of the MV is not reflected into the RV. In this
case, the updated information of the MV is managed as the difference between the MV and RV contents
so that the difference can be reflected into the RV when Replicate/Restore is executed subsequently.
When the Synchronous State (sync) is placed after Restore(protect) is executed, it is automatically
changed to the Separated State (separated).
When data of MV is referred to during Restore execution, the user can refer to the content of RV
immediately after the instruction to start Restore even if the content of RV has not been completely
reflected to MV. This is done by obtaining data from RV when the area where difference copy from
RV to MV has not been completed is accessed in response to a reference request to MV.
Update to MV
Restore
operation starts
MV
RV
Separate State
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Update to MV
MV
RV
Restore Execution
Figure 2-5 Restore and State Transitions
15
Chapter 2 Data Replication
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Until the
difference is zero
Only when
updating RV
Synchronous State
Restore State
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Update to MV
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