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With the Global Mirror method, there is a design option that assists with low bandwidth for the
IBM Flex System V7000 Storage Node and the other IBM virtual storage systems that are
mirroring to it running 6.4.1 code level. This option uses change volumes associated with the
primary and secondary volumes. These volumes are used to record changes to the remote
copy volume, the FlashCopy relationship that exists between the secondary volume and the
change volume, and between the primary volume and the change volume. This function is
called Global Mirror cycling mode. Figure 2-20 shows an example of this function where you
can see the relationship between volumes and change volumes.
Support: Though this feature was added in the 6.3 code level, only 6.4.1code level is
supported to mirror to the IBM Flex System V7000 Storage Node.
Figure 2-20 Global Mirror with change volumes
In asynchronous Remote Copy, the application acknowledges that the write is complete
before the write is committed at the secondary. Hence, on a failover, certain updates (data)
might be missing at the secondary. The application must have an external mechanism for
recovering the missing updates, if possible. This mechanism can involve user intervention.
Recovery on the secondary site involves starting the application on this recent "backup" and
then rolling forward or backward to the most recent commit point.
2.6.5 Copy Services configuration limits
In Table 2-8, we describe the Copy Services configuration limits. For the most up-to-date list
of these limits, see the following website:
http://www.ibm.com/support/docview.wss?uid=ssg1S1003702&myns=s028&mynp=familyind54
02112&mync=E
Table 2-8 Copy Services configuration limits
Properties
Remote Copy (Metro Mirror and
Global Mirror) relationships per
clustered system
Remote Copy relationships per
consistency group
Maximum number
4096
4096
Chapter 2. Introduction to IBM Flex System V7000 Storage Node
Comments
This configuration can be any
mix of Metro Mirror and Global
Mirror relationships.
No additional limit is imposed
beyond the Remote Copy
relationships per clustered
system limit.
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