[Linux-cluster] Quorum question / split brain paranoia

[Lon Hohberger]

On Thu, Sep 06, 2007 at 09:30:55AM -0400, Christopher Barry wrote:
> On Thu, 2007-09-06 at 08:22 -0400, Lon Hohberger wrote:
> > On Wed, Sep 05, 2007 at 06:16:32PM -0400, Christopher Barry wrote:
> > > 
> > > The cluster nodes will run GFS, the director will not. Only one director
> > > will be active with a VIP, load will balance across all 6 VMs. The
> > > crossover will actually have VLANs on it that will allow a separate
> > > heartbeat net, but it was getting a bit tricky with ASCII art ;)
> > > 
> > > Can anyone see any issues that may arise where quorum could create a
> > > split brain scenario? What would be the best way to approach votes, etc.
> > > here?
> > 
> > So, two physical boxes hosting LVS to virtual machines as the real
> > servers (how ironic, actually...).  Said real server cluster is using
> > GFS to share the data?
> > 
> > (I want to make sure I understand the question here)
> > 
> 
> 
> Hi Lon,
> 
> It is a bit ironic, isn't it ;) Yes, you are correct; the vm
> real-servers are sharing a gfs volume.

No real issues, but your qdiskd heuristics should be based on "can I
talk to a physical node in the cluster" or something like that.

Basically, you need to implement a solution which will allow all-but-one
node to fail in the "virtual machine" cluster.  This way, if you lose
half of the VMs, you can still maintain a quorum.

-- 
Lon Hohberger - Software Engineer - Red Hat, Inc.