IBM Flex System V7000 Expansion Enclosure 4939H29 사용자 설명서
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4939H29
Chapter 9. IBM Flex System V7000 Storage Node Copy Services
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Draft Document for Review January 29, 2013 12:52 pm
8068ch09-Copy Servies.fm
This situation provides an always consistent image at the target site and protects your data
from being inconsistent during re synchronization.
from being inconsistent during re synchronization.
Take a closer look at how Change Volumes might reduce replication traffic.
Figure 9-64 shows a number of I/Os on the source volume and the same number on the
target volume, and in the same order. Assuming that this set is the same set of data being
updated over and over, then these updates are wasted network traffic and the I/O can be
completed much more efficiently (Figure 9-65).
target volume, and in the same order. Assuming that this set is the same set of data being
updated over and over, then these updates are wasted network traffic and the I/O can be
completed much more efficiently (Figure 9-65).
Figure 9-64 Global Mirror I/O replication without Change Volumes
In Figure 9-65, the same data is being updated repeatedly, so Change Volumes demonstrate
significant IO transmission savings, because you only need to send I/O number 16, which
was the last I/O before the cycling period.
significant IO transmission savings, because you only need to send I/O number 16, which
was the last I/O before the cycling period.
Figure 9-65 Global Mirror I/O replication with Change Volumes
The cycling period can be adjusted by running
chrcrelationship -cycleperiodseconds
<60-86400>
. If a copy does not complete in the cycle period, the next cycle does not start until
the prior one has completed. It is for this reason that using Change Volumes gives you two
possibilities for RPO:
possibilities for RPO:
If your replication completes in the cycling period, then your RPO is twice the
cycling period.
cycling period.
If your replication does not complete within the cycling period, then your RPO is twice the
completion time. The next cycling period starts immediately after the prior one is finished.
completion time. The next cycling period starts immediately after the prior one is finished.
Careful consideration should be put into balancing your business requirements with the
performance of Global Mirror with Change Volumes. Global Mirror with Change Volumes
increases the inter-cluster traffic for more frequent cycling periods, so going as short as
possible is not always the answer. In most cases, the default should meet your requirements
and perform reasonably well.
performance of Global Mirror with Change Volumes. Global Mirror with Change Volumes
increases the inter-cluster traffic for more frequent cycling periods, so going as short as
possible is not always the answer. In most cases, the default should meet your requirements
and perform reasonably well.