[ClusterLabs] Fencing on 2-node cluster

[Andrei Borzenkov]

21.06.2018 00:50, Digimer пишет:
> On 2018-06-20 05:46 PM, Jehan-Guillaume de Rorthais wrote:
>> On Wed, 20 Jun 2018 17:24:41 -0400
>> Digimer <lists at alteeve.ca> wrote:
>>
>>> Make sure quorum is disabled. Quorum doesn't work on 2-node clusters.
>>
>> It does with the "two_node" parameter enabled in corosync.conf...as far as I
>> understand it anyway...
> 
> It doesn't, that option disables quorum in corosync.
> 

This option does not disable quorum - this option fakes quorum so
corosync continues to report "in quorum" even when one node is lost. it
is quite possible that pacemaker quorum does not map one-to-one to
corosync quorum though.

> Quorum is floor(($nodes / 2) + 1). So in a 3-node, that is 3 -> 1.5 ->
> 2.5 -> 2 votes needed for quorum. In a 2-node, that is 2 -> 1 -> 2 -> 2
> votes needed for quorum, meaning you can't lose a node to operate (which
> is kinda not HA :) ).
> 

Yes, but that assumes normal, non two_node, configuration. As said,
two_node makes corosync to always pretend quorum is available (after
initial implicit wait_for_all).