150 IBM System Storage DS6000 Series: Copy Services in Open Environments
Planned outages
The planned outage procedures rely on two facts:
򐂰 Metro Mirror source and target volumes are in a consistent and current state.
򐂰 Both DS6000s are functional and reachable.
You can swap sites without any full copy operation by combining Metro Mirror initialization
modes.
Unplanned outages
In contrast to the assumptions for planned outages, the situation in a disaster is more difficult:
򐂰 In an unplanned outage situation, only the DS6000 at the recovery site is functioning.
The production site DS6000 might be lost or unreachable.
򐂰 In an unplanned situation, volumes at the production and recovery site might be in
different states.
򐂰 As opposed to a planned situation in which you can stop all I/Os at the production site to
make all volumes across the recovery site reach a consistent status, you cannot do this in
an unplanned situation. If you are not using Consistency Groups, and, for example, the
power fails, you can only assume consistency at the level of a single volume pair, not at
the application level.
14.8.1 Metro Mirror Failover function
In our example, we have used the Metro Mirror environment shown in Figure 14-4. We have
four Metro Mirror source volumes in DS6000#1 (serial number 1300819) at the production
site, and four Metro Mirror target volumes in DS6000#2 (serial number 1300247) at the
recovery site. We call the volumes at the production site, A volumes, which initially are Metro
Mirror source volumes. We call the volumes at the recovery site, B volumes, which initially are
Metro Mirror target volumes. During operations to switch sites, A and B volumes become
alternatively source and target; therefore, we add the A and B terminology for clarification.
Figure 14-4 Metro Mirror environment for example of switching sites
LSS14
1400
1401
LSS15
1500
1501
LSS1A
1A00
1A01
LSS1B
1B00
1B01
FCP links
Metro Mirror paths
Metro Mirror Pairs
DS6000#2
-dev IBM.1750-1300247
DS6000#1
-dev IBM.1750-1300819
Source
(A volumes)
Target
(B volumes)
Metro Mirror Pairs

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