[Linux-HA] Redundant Rings "Still Not There?"

Serge Dubrouski sergeyfd at gmail.com
Sat Oct 23 10:59:56 MDT 2010

On Fri, Oct 22, 2010 at 5:27 PM, Robinson, Eric <eric.robinson at psmnv.com> wrote:
>>> I am building a 3-node cluster and adding it to a network that
> already
>>> had a separate 2-node cluster.
>>> The new 3-node cluster would have 2 nodes actively serving up
>>> resources with 1 node acting as a failover for both of the active
> nodes.
>> In this case all 3 nodes have to be connected to all rings
>> if you want to use those rings for Pacemaker communications.
>> And those rings have to be separate from existing cluster rings.
> So in my case, each of the back-to-back connections (crossover cables)
> would be regarded as a separate ring?

Looks like you are mixing up physical connections and Corosync rings.
Ring is an abstraction in Corosync. Crossover cable is a physical
connection. DRBD doesn't need a Corosync "ring" for data replication,
you can use your crossovers for that. Pacemaker/Corosync membership
protocol though requires that all nodes were connected to the same
network and form one or more abstract "rings" to communicate to each
other. That means that using crossovers you can't build a cluster with
more that 2 nodes.

With that said if you have 3 servers connected to one network and also
forming 2 cross-connected pairs you can build a 3 node cluster with 1
Corosync ring for Pacemaker communication and also use your crossovers
for DRBD data replication. But those crossovers won't be considered as
a Corosync rings. If you want to have real redundancy rings you have
to replace your crossovers with a switch and connect all 3 nodes to
it. To have more rings you have to add more switches.

> --
> Eric Robinson
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Serge Dubrouski.

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