Quoting Jaap Winius <[email protected]>:
My RHEL7 project is considering using DRBD to create sets of 2 x
2-nodes that replicate synchronously across two data centers. The
first half of each set would consist of a primary and a secondary
with the latter taking over in case of failure (Heartbeat-based
Pacemaker cluster). However, the same block device(s) should also
replicate to the second half of the set in the second data center.
Crucially, it should be possible to turn these roles around without
too much effort when the choice is made to make the second data
center active and the first one passive.
Is this possible with DRBD and if so, what kind of replication
configuration should be used?
Yes. First, install DRBD9 on all four nodes to create a single
replicating DRBD cluster. Next, install the pcs and pacemaker packages
(which include Corosync as dependency instead of Heartbeat) on the
same four nodes, but don't use them to create a single
Corosync/Pacemaker cluster. Rather, create two clusters -- one in each
data center -- of two nodes each, ensuring that DRBD continues to
replicate across all four nodes and that only one of the two
Corosync/Pacemaker clusters is active at a time. This way, failovers
and failbacks will only involve two nodes in the data center where the
Corosync/Pacemaker cluster is active. Use your preferred configuration
management software to stop the Corosync/Pacemaker cluster in one data
center and start it in the other, automatically moving the DRBD
primary along with it.
Cheers,
Jaap
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