[Openais] quorum service question

Christine Caulfield ccaulfie at redhat.com
Tue Nov 17 05:55:28 PST 2009

On 17/11/09 10:59, Dietmar Maurer wrote:
>>> But AFAIK this information is local (not copied to other nodes). And
>> the votequorum seems to add new nodes dynamically. So how can I make
>> sure that all nodes in the cluster use the same values? I guess it is
>> important that all nodes start with the same value?
>>> Or is it better to not set expected_votes at start:
>>> quorum {
>>>           provider: corosync_votequorum
>>> 	  votes: 1
>>> }
>>> And set expected_votes later with an application that has static
>> knowledge about all cluster members?
>> The quorum service really works best if you have a common configuration
>> system so that the values are the same on all nodes.
> The question is how to do that. Quorum setting are read from /etc/corosync/corosync.conf, but there is no way to write that file - the confdb interface is read-only?

That's currently down to you, sadly. Red Hat cluster has a mechanism for 
distributing its configuration file and of making corosync re-reading it 
when necessary. But really, it's not a hard job with a bit of scripting 
and and SSH key.

Actually confdb does support writing, it's just that most of the 
back-end configuration modules don't ... yet.

>> Having said that it should always use the highest expected_votes value,
>> so as you add nodes (with, I hope, increasing values for
>> expected_votes!) then the quorum requirement will increase. So although
>> the actual values for expected_votes per node are not replicated, the
>> effect is.
> This does not work when the cluster is partitioned. If you start with low expected_votes settings both partitions can get quorate?

That's why you should be careful, and always share your configuration 
files :-)


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