Metro/Global Mirror Volume Configuration - IBM DS8000 User Manual

For Global Mirror processing, one storage unit at the intermediate site is
designated as the master storage unit. The master storage unit sends commands
over Fibre Channel Protocol (FCP) links and coordinates the consistency group
formation process. These links are required for the Global Mirror master storage
unit to coordinate the consistency group formation process with the storage units
and to communicate the FlashCopy commands to the remote site. All status is
relayed back to the master storage unit.
How Metro/Global Mirror works
In order to understand how Metro/Global Mirror works, it is important to
understand how the volumes are configured at each site.
Figure 12 shows a Metro/Global Mirror environment that includes the A, B, C, and
D volume configuration at the three sites.
There are three volume configurations in a Metro/Global Mirror environment:
v Volumes at the local (or primary) site are Metro Mirror primary (or source)
v Volumes at the intermediate site are the Metro Mirror secondary (or target)
v One set of volumes at the remote site are the Global Mirror secondary volumes
Figure 12. Metro/Global Mirror volume configuration
The Global Mirror function allows you to combine a Global Copy volume pair
with FlashCopy such that the Global Copy secondary also serves as the FlashCopy
source in a Global Mirror session. FlashCopy plays an integral part of this
configuration because the set of volumes that are FlashCopy target volumes
contain consistent data. This set of volumes is called a consistency group.
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DS8000 User's Guide
volumes and are referred to as the A volumes.
volumes and Global Mirror primary volumes at the same time. These volumes
are referred to as the B volumes. (If additional volumes are used at the
intermediate site as FlashCopy target volumes, they are referred to as E
volumes.)
and FlashCopy source volumes at the same time. These volumes are referred to
as the C volumes. The FlashCopy target volumes are referred to as the D
volumes.
Local Site
A
volumes
Metro
Mirror
Primary
Metro Mirror
(Cascaded Volume)
Intermediate
Site
B C
volumes volumes
Metro Mirror
Global Copy
Secondary
Secondary
Global Copy FlashCopy
Primary Source
Remote Site
D
volumes
FlashCopy
Target
Global Mirror