[Pacemaker] stonith and avoiding split brain in two nodes cluster

[Angel L. Mateo]

El 25/03/13 20:50, Jacek Konieczny escribió:
> On Mon, 25 Mar 2013 20:01:28 +0100
> "Angel L. Mateo" <amateo at um.es> wrote:
>>> quorum {
>>> 	provider: corosync_votequorum
>>> 	expected_votes: 2
>>> 	two_node: 1
>>> }
>>>
>>> Corosync will then manage quorum for the two-node cluster and
>>> Pacemaker
>>
>>    I'm using corosync 1.1 which is the one  provided with my
>> distribution (ubuntu 12.04). I could also use cman.
>
> I don't think corosync 1.1 can do that, but I guess in this case cman
> should be able provide this functionality.
>
	Sorry, it's corosync 1.4, not 1.1.

>>> can use that. You still need proper fencing to enforce the quorum
>>> (both for pacemaker and the storage layer – dlm in case you use
>>> clvmd), but no
>>> extra quorum node is needed.
>>>
>>    I hace configured a dlm resource usted with clvm.
>>
>>    One doubt... With this configuration, how split brain problem is
>> handled?
>
> The first node to notice that the other is unreachable will fence (kill)
> the other, making sure it is the only one operating on the shared data.
> Even though it is only half of the node, the cluster is considered
> quorate as the other node is known not to be running any cluster
> resources.
>
> When the fenced node reboots its cluster stack starts, but with no
> quorum until it comminicates with the surviving node again. So no
> cluster services are started there until both nodes communicate
> properly and the proper quorum is recovered.
>
	But, will this work with corosync 1.4? Alghtough with corosync 1.4 I 
may won't be able to use quorum configuration you said (I'll try), I 
have configured no-quorum-policy="ignore" so the cluster could still run 
in the case of one node failing. Could this be a problem?

-- 
Angel L. Mateo Martínez
Sección de Telemática
Área de Tecnologías de la Información
y las Comunicaciones Aplicadas (ATICA)
http://www.um.es/atica
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