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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.

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.

Local Site

Subordinate

Master

Remote Site

FlashCopy

Intermediate Site

Metro

Mirror

f2c00504

Global Copy

Long Distance

Figure 13. Metro/Global Mirror configuration with master and subordinate storage units

Chapter 8. Optional feature codes for the DS8000 121

IBM DS8000 User Manual

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