[ClusterLabs] Fencing on 2-node cluster

[Digimer]

On 2018-06-20 11:52 PM, Andrei Borzenkov wrote:
> 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.

Technically correct, which is the best kind of correct.

I didn't go into that detail as the results are the same (and consistent
with pacemaker's quorum=false language).

>> 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).
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-- 
Digimer
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