[Linux-cluster] How to disable node?

Rick Stevens ricks at nerd.com
Mon Aug 31 21:22:07 UTC 2009

Jakov Sosic wrote:
> On Mon, 31 Aug 2009 15:30:13 -0500
> Alan A <alan.zg at gmail.com> wrote:
>> You have to give your cluster 2 node setting on remaining two nodes.
>> How can I define a two-node cluster if a majority is needed to reach
>> quorum?
>> We had to allow two-node clusters, so we made a special exception to
>> the quorum rules. There is a special setting "two_node" in
>> the /etc/cluster.conf file that looks like this:
>> <cman expected_votes="1" two_node="1"/>
>> This will allow one node to be considered enough to establish a
>> quorum. Note that if you configure a quorum disk/partition, you don't
>> want two_node="1".
>> http://sources.redhat.com/cluster/wiki/FAQ/CMAN#two_node
> Yeah I know how to set up two_node cluster, but didn't know that
> reconfiguration is the only way out when one node is missing :( I'm
> disappointed with this limitation, I hope that developers will sort it
> out for RHEL6 :(

I don't see that there's anything to fix.  You had a three-node cluster
so you needed a majority of nodes up to maintain a quorum.  One node
died, killing quorum and thus stopping the cluster (the expected and
correct behavior).  As a three-node cluster, it's dead.  It can't be run 
as a three-node cluster until the third node is fixed.  Those are the

A two node cluster requires special handling of things to prevent the
dread split-brain situation, which is what two_node does.  Running the
surviving nodes as a two-node cluster is, by definition, a
reconfiguration.  I'd say simply requiring you to set two_node is pretty
damned innocuous to let you run a dead (ok, mortally wounded) cluster.

If you pulled a drive out of a RAID6--thus degrading it to a RAID5--
would you complain because it didn't remain a RAID6?
- Rick Stevens, Systems Engineer                      ricks at nerd.com -
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