[Pacemaker] RHEL6.x dependency between 2-node-settings for cman and quorum settings in pacemaker

[Andreas Mock]

Hi Andrew,

that means (when I understand it right), that with this setting
you get two different semantics about what the cluster knows
about itself.

With setting of a+c as recommended by you the 2-node-cluster
does not get quorum in case only one node survives, but ignores
that info.

With the setting of b) the cluster does get quorum even when
only one node is left. In this case I need not set c) as pacemaker
believes having quorum (told by cman).

Is this right?

Best regards
Andreas


-----Ursprüngliche Nachricht-----
Von: Andrew Beekhof [mailto:andrew at beekhof.net] 
Gesendet: Montag, 15. April 2013 05:58
An: The Pacemaker cluster resource manager
Betreff: Re: [Pacemaker] RHEL6.x dependency between 2-node-settings for cman
and quorum settings in pacemaker


On 12/04/2013, at 4:58 PM, Andreas Mock <Andreas.Mock at web.de> wrote:

> Hi all,
> 
> another question rised up while reading documentation concerning 
> 2-node-cluster under RHEL6.x with CMAN and pacemaker.
> 
> a) In the quick start guide one of the things you set is
> CMAN_QUORUM_TIMEOUT=0 in /etc/sysconfig/cman to get one node of the 
> cluster up without waiting for quorum. (Correct me if my understanding 
> is wrong)
> 
> b) There is a special setting in cluster.conf  <cman two_node="1" 
> expected_votes="1" >  </cman> which allows one node to gain quorum in 
> a two node cluster (Please also correct me here if my understanding is 
> wrong)
> 
> c) And there is a pacemaker setting
> no-quorum-policy which is mostly set to 'ignore' in all startup 
> tutorials.
> 
> My question: I would like to understand how these settings influence 
> each other and/or are dependent.

a) allows "service cman start" to complete (and therefor allow "service
pacemaker start" to begin) before quorum has arrived.
b) is a possible alternative to a) but I've never tested it because it is
superseded by c) and in fact makes c) meaningless since the cluster always
has quorum.

a+c is preferred for consistency with clusters of more than 2 nodes.

> 
> As most insight as possible appreciated. ;-)
> 
> Best regards
> Andreas
> 
> 
> 
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