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Re: [Linux-cluster] quorum



Hi Jakov,

 I got your points , thanks a lot

Regards
Prathyush


On Wed, Apr 3, 2013 at 11:16 PM, Jakov Sosic <jsosic srce hr> wrote:
> On 03/22/2013 02:42 AM, Prathyush wrote:
>> 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
>
> That's the exactly as should be.
>
> When you have 3 node cluster, and first node goes down - it's irrelevant
> if it went down by standard shutdown or by pulling the cord, other two
> nodes still have enough votes to hold the quorum.
>
> But now you're on just 2 out of 3 votes and things get a little bit more
> complicated.
>
> If you shut down one of the remaining two nodes by standard shutdown
> procedure, cman service will announce that the node is leaving cluster
> (ccs_tool leave).
>
> Other node will now know that he's the only one left, and although it
> won't have quorum, it will continue to provide services. It does not
> have a reason not to, cluster was disassembled nicely.
>
>
> But, if you pull out power out of one of the two remaining nodes,
> simulating it's crash, it's OK for the remaining node to stop providing
> services. He just doesn't know what's happening to other node, other
> node could think the same and you would get split-brain scenario.
>
> One thing that could solve your problem is introduction of quorum disk,
> which would hold 2 votes, so in the latter scenario, one node that
> survives would make scsi reservation on quorum disk and would thus hold
> 3 out of 5 votes.
>
> What kind of fencing are you using? Is it IPMI?
>
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--
Regards,
Prathyush


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