[Linux-cluster] quorum

[Digimer]

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.

digimer

On 03/22/2013 03:16 AM, emmanuel segura wrote:
> Hello
>
> 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
>
> Thanks
>
> 2013/3/22 Prathyush <prathyush.r at gmail.com <mailto:prathyush.r at gmail.com>>
>
>     HI,
>
>
>     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
>     --
>     /*Regards,
>     Prathyush*/


-- 
Digimer
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