

Re: [Linux-cluster] quorum

I have the below scenario,
I have made the first node down the service failover to second node,then I switched off second node ,service again swiched to third node,the quorum was not lost,it adjusted automatically

On Mar 22, 2013 9:11 PM, "Digimer" <lists alteeve ca> wrote:
This is correct.

Quorum needs "50% + 1" of the votes. So in Prathyush's cluster of 3 nodes/3 votes;

3 / 2 == 1.5 rounded up is 2.

So once the second node shut down, quorum was lost. With quorum lost, the remaining node will stop all of it's clustered services because it can no longer be sure what the other nodes are doing. For example, the other two nodes might turn back on, fail to connect to the one remaining node, decide they have quorum and start clustered services. This would lead to a split brain.

If you want a 3-node cluster to work with just one node, consider adding a quorum disk, assuming you have a SAN. This would add 2 votes to the cluster. So the new math would be;

5/2 == 2.5 rounded up to 3.

The quorum disk would give it's two votes to the remaining single node for a total of 3 votes, thus giving it quorum and allowing it to operate on it's own.


On 03/22/2013 03:16 AM, emmanuel segura wrote:

If i understand well, you 3 node(3 total votes) and you poweroff 2, 3 -
2 = 1(quorum loss) remain less 50% of votes

can you show your config and your log, without it's so hard help you


2013/3/22 Prathyush <prathyush r gmail com <mailto:prathyush r gmail com>>


    I have 3 node  cluster with 1 vote each ,and  decided to shut down
    the 2 nodes for  maintenance .
    When a proper power off /init 0 given to two of the nodes ,i never
    loses the quorum
    When i am making  force power off (switching off the power/pulling
    the power cable) quorum  was lost and services failed in the third node.
    why this is happening... any idea

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