[Linux-cluster] GFS on SAN, does a quorum make sense?

[Lon Hohberger]

On Fri, 2005-05-06 at 13:58 -0400, Dan B. Phung wrote:
> > You can do it manually by adjusting cman_tool's expected votes down to a
> > small number while doing a one-node boot, but please ensure the rest of
> > the cluster is down before doing so.
> 
> ah, I see, and that would overide the cluster.conf node/vote counts.  

Yes.

> Woudn't another way be to somehow mark the file system with a unique
> cluster id (randomly generated) so that mounting would fail if the cluster
> isn't part of the other clusters?  ...or rather, at a higher level, what
> would help is an inband locking mechanism.  I guess I should start reading
> the design docs and published papers to see how this would work.

Well, the cluster doesn't form a quorum based on the ability to mount
the file system.  Rather, to mount on a given node, that node must
already be a member of the cluster quorum.

You could use something like SCSI reservations or fibre-channel fencing
(FC zoning) as an additional measure to prevent the other nodes from
being able to access the storage at all, but you'll still have to do the
CMAN trick in order to get it up to a quorate state where you can mount.

-- Lon