[Linux-cluster] Two node cluster - a potential problem of node fencing each other?

[Ian Hayes]

On Sat, Mar 12, 2011 at 11:19 PM, Parvez Shaikh
<parvez.h.shaikh at gmail.com>wrote:

> Hi all,
>
> I have a question pertaining to two node cluster, I have RHEL 5.5 and
> cluster along with it which at least should have two nodes.
>
> In a situation where both nodes of the cluster are up, and have reliable
> connection to fencing device (e.g. power switch OR any other power fencing
> device) and heartbeat link between two nodes goes down.
>
> Each node finds another node is down (because heartbeat IP becomes
> unreachable) and tries to fence each other.
>
> Is this situation possible? If so, can two nodes possibly fence (in short
> shutdown or reboot) each other? Is there anyway out of this situation?
>

This is a fairly common problem called "split brain". The two nodes will go
into a shootout, fencing each other. There are a few ways to prevent this,
such as redundant network links and the use of quorum disks.
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