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A Metro/Global Mirror environment is configured using a minimum of three
storage units, one each at the local, intermediate, and remote sites. Data from the A
volumes at the local site is synchronously replicated to B volumes at the
intermediate site using Metro Mirror. Data from the B volumes at the intermediate
site is asynchronously replicated to the C volumes at the remote site using Global
Copy. FlashCopy relationships that are created with the C volumes at the remote
site become the FlashCopy source volumes and the D volumes at the remote site
become the FlashCopy target volumes.
Note: For ease of understanding, we describe the Metro/Global Mirror
configuration in terms of the local, intermediate, and remote sites. You can
manage the volumes that are associated with the storage units at these sites
from one central location.
For Metro/Global Mirror, one storage unit at the intermediate site is designated as
the master. Optional additional storage units at the intermediate site, if configured,
are designated as subordinates. The master sends commands to its subordinate
storage units over fibre channel protocol (FCP) links and coordinates the
consistency group formation process over all the subordinate storage units. The
FCP links also enable the Global Mirror master storage unit to communicate the
FlashCopy commands to the remote site. All status is then relayed back to the
master storage unit. Figure 13 provides a high-level view of the three-site
Metro/Global Mirror configuration.
Metro
Mirror
Local Site
Figure 13. Metro/Global Mirror configuration with master and subordinate storage units
In a Metro/Global Mirror configuration, if you lose access to the storage unit at the
local site, the Global Copy relationship is intact and Global Mirror is still
operational. Through the use of FlashCopy operations and consistency groups,
consistent data is maintained at the remote site. However, you are left without the
local site until all recovery operations have been performed to recover the local
site.
Subordinate
Subordinate
Master
Intermediate Site
Chapter 8. Optional feature codes for the DS8000
Global Copy
Long Distance
Remote Site
FlashCopy
FlashCopy
FlashCopy
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