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Chapter 2 Data Replication
19
2
2
2
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5
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R
R
R
e
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e
l
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If the copy control state is set to the Synchronized Copy state, the difference between MV and RV is
not accumulated because updates to MV are immediately reflected to RV. However, the write time to
MV is longer because it waits for reflection of the updates to RV. If the Copy Control state is set to
the Suspend state, the difference between MV and RV is accumulated because updates to MV are not
reflected to RV, but the write time to MV is the same as normal I/O.
In this way, there are correlations between the amount of accumulated differences in MV and RV and
write performance in different copy control states. The correlation for each copy control state is
shown in Table 2-3.
Table 2-3 Correlations in Different Copy Control States
Copy Control State Difference between MV and RV Write Overhead to MV
Foreground (Synchronous) Small Exists
Foreground
(Semi-synchronous)
Background
Suspend Large Does not exist
If the difference between MV and RV is large in the Replicate state, we recommend to select a copy
control state which gives the difference between MV and RV smaller in a system without sufficient
suspension time for Separate execution because the processing time of Separate increases. Also, we
recommend you to select a copy control state without write overhead to MV in a system where write
performance to MV must be maintained and improved.