[Pacemaker] pingd

[Lars Ellenberg]

On Fri, Sep 03, 2010 at 12:12:58PM +0200, Bernd Schubert wrote:
> > > >> PS: (*) As you insist ;) on quorum with n/2 + 1 nodes, we use ping as
> > > >> replacement. We simply cannot fulfill n/2 + 1, as controller failure
> > > >> takes down 50% of the systems (virtual machines) and the systems
> > > >> (VMs) of the 2nd controller are then supposed to take over failed
> > > >> services. I see that n/2 + 1 is optimal and also required for a few
> > > >> nodes. But if you have a larger set of system (e.g. minimum 6 with
> > > >> the VM systems I have in my mind) n/2 + 1 is sufficient, IMHO.
> > > > 
> > > > You meant to say you consider == n/2 sufficient, instead of > n/2 ?
> > 
> > So you have a two node virtualization stuff, each hosting n/2 VMs,
> > and do the pacemaker clustering between those VMs?
> 
> Yes.
> 
> > 
> > I'm sure you could easily add "somewhere else" a very bare bone VM
> > (or real) server, that is dedicated member of your cluster, but
> > never takes any resources? Just serves as arbitrator? as your "+1"?
> 
> No, I'm afraid it is not that easy. There is simply is nothing that can be 
> used. If there is anything, it is always available on both hosts/controllers. 
> Imagine you would sell a standalone DRBD system (black box), that provides for 
> example NFS to clients. You would want to have each and every additional 
> service mirrored again. And you could not rely on additional customer NFS 
> clients.
> 
> > 
> > May be easier, safer, and more transparent than
> > no-quorum=ignore plus some ping attribute based auto-shutdown.
> 
> I agree on safer and transparent, but unfortunately, it not easier in our 
> case.

Sell a Sheevaplug together with the two blackboxes,
and tell them to plug it into somewhere.
Yeah, well, maybe an other micro thingy with two ethernet adapters,
so you can plug it into your fully redundant network topology ;-)

Something like that.

-- 
: Lars Ellenberg
: LINBIT | Your Way to High Availability
: DRBD/HA support and consulting http://www.linbit.com

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