Справочник Пользователя для IBM Flex System V7000 Expansion Enclosure 4939H29
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4939H29
Chapter 9. IBM Flex System V7000 Storage Node Copy Services
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Figure 9-61 Global Mirror write sequence
The Global Mirror algorithms maintain a consistent image on the auxiliary volume at all times.
They achieve this consistent image by identifying sets of I/Os that are active concurrently at
the master, assigning an order to those sets, and applying those sets of I/Os in the assigned
order at the secondary.
They achieve this consistent image by identifying sets of I/Os that are active concurrently at
the master, assigning an order to those sets, and applying those sets of I/Os in the assigned
order at the secondary.
In a failover scenario, where the secondary site needs to become the master source of data,
depending on the workload pattern and the bandwidth and distance between local and
remote site, certain updates might be missing at the secondary site. Therefore, any
applications that use this data must have an external mechanism for recovering the missing
updates and reapplying them, for example, a transaction log replay.
depending on the workload pattern and the bandwidth and distance between local and
remote site, certain updates might be missing at the secondary site. Therefore, any
applications that use this data must have an external mechanism for recovering the missing
updates and reapplying them, for example, a transaction log replay.
9.3.2 Global Mirror with Change Volumes
Global Mirror within the IBM Flex System V7000 Storage Node is designed to achieve a
recovery point objective (RPO) which is as low as possible, so that data is as up-to-date as
possible. This capability places some strict requirements on your infrastructure and in certain
situations, with low network link quality or congested or overloaded hosts, you maybe
impacted by multiple 1920 (congestion) errors.
recovery point objective (RPO) which is as low as possible, so that data is as up-to-date as
possible. This capability places some strict requirements on your infrastructure and in certain
situations, with low network link quality or congested or overloaded hosts, you maybe
impacted by multiple 1920 (congestion) errors.
Congestion errors happen in three primary situations:
1. Congestion at the source site through the host or network
2. Congestion on the network link or network path
3. Congestion at the target site through the host or network
With all releases after 6.3.0, Global Mirror picked up new functionality that is designed to
address a few conditions that were negatively effecting some Global Mirror implementations:
address a few conditions that were negatively effecting some Global Mirror implementations:
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Estimation of bandwidth requirements tends to be complex.
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It is often difficult to guarantee the latency and bandwidth requirements can be met.
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Congested hosts on either the source or target site can cause disruption.
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Congested network links can cause disruption with only intermittent peaks.