[Linux-cluster] Two nodes cluster issue without sharedstorageissue

[Jeff Sturm]

Certainly.  That third node need not run any cluster services at all other than fencing, and yet would guarantee a quorum in the even of loss of any single node.
 
A quorum disk would theoretically solve this as well, but for reasons I can't quite articulate I suspect the three-node cluster is superior.  (Besides, we have stockpiles of cheap hardware where I'm at, so there's little reason for us not to do it.)

________________________________

	From: linux-cluster-bounces at redhat.com [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Rodrique Heron
	Sent: Friday, October 24, 2008 12:00 PM
	To: linux clustering
	Subject: Re: [Linux-cluster] Two nodes cluster issue without sharedstorageissue
	
	
	Jeff
	
	I have two node cluster only because my storage array only supports two nodes, can I add a third node without it having access to the storage? I am using CLVM to run domU's.
	
	
	
	Jeff Sturm wrote: 

		For what it's worth, considerations like these have caused us to abandon any efforts to build a 2-node cluster.
		
		>From this point forward all our RHCS deployments will have a minimum of 3 nodes, even if the 3rd node is a small node that provides no resources and only exists for arbitration purposes.  (It was going to be that, or a quorum disk for our application, but we have no experience running a quorum disk over the long-haul in a production envrironment.)
		
		Hope this helps someone.
		
		> -----Original Message-----
		> From: linux-cluster-bounces at redhat.com
		> [mailto:linux-cluster-bounces at redhat.com] On Behalf Of Chen,
		> Mockey (NSN - CN/Cheng Du)
		> Sent: Thursday, October 23, 2008 10:36 PM
		> To: linux clustering
		> Subject: RE: [Linux-cluster] Two nodes cluster issue without
		> sharedstorageissue
		>
		> 
		>
		> >-----Original Message-----
		> >From: linux-cluster-bounces at redhat.com
		> >[mailto:linux-cluster-bounces at redhat.com] On Behalf Of ext Lon
		> >Hohberger
		> >Sent: 2008年10月24日 0:02
		> >To: linux clustering
		> >Subject: Re: [Linux-cluster] Two nodes cluster issue without shared
		> >storageissue
		> >
		> >On Thu, 2008-10-16 at 17:10 +0800, Chen, Mockey (NSN - CN/Cheng Du)
		> >wrote:
		> >> Hi,
		> >>
		> >> I want to set up a two node cluster, I use active/standby
		> >mode to run
		> >> my service. I need even one node's hardware failure such as
		> >power cut,
		> >> another node still can handover from failure node and the
		> >provide the
		> >> service.
		> >>
		> >> In my environment, I have no shared storage, so I can not
		> use quorum
		> >> disk. Is there any other way to implement it? I searched and found
		> >> 'tiebreaker IP' may feed my request, but I can not found any
		> >hints on
		> >> how to configure it ?
		> >
		> >Since you have no shared data, you may be able to run
		> without fencing.
		> >
		> >That should be pretty straightforward, but you might need to comment
		> >out the "fenced" startup from the cman init script.
		> >
		> >In this case, the worst that will happen is both nodes will end up
		> >running the service at the same time in the event of a network
		> >partition.
		> >
		> >The other down side is that if the cluster divides into two
		> partitions
		> >and later merges back into one partition, I don't think
		> certain things
		> >will work right; you will need to detect this event and
		> reboot one of
		> >the nodes.
		> >
		> >-- Lon
		>
		> I know such defects in two node cluster. 
		> Since our service is mission critical, I want to know how to
		> avoid such failure case ?
		>
		> Thanks.
		>
		>
		>
		> --
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		>
		
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	-- 
	Rodrique Heron 
	

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