[Users] oVirt 3.5 planning

[Jorick Astrego]

Hi,

Currently we have some small server clusters that have only two storage
nodes with iSCSI. I would like to use Gluster bricks for them but I'm a
bit worried about quorum and split-brain.

Would it be an idea to make ovirt a Gluster quorum arbiter? The ovirt
engine is managing the virtual datacenter and could easily be the
deciding factor when a 2 brick gluster loses one of the bricks.

http://hekafs.org/index.php/2012/11/different-forms-of-quorum/

The second issue is trickier. What should we do when N=2? In some cases,
allowing a single failure to make a volume read-only (the current
behavior) is fine. In others it’s not. One idea would be to “promote”
from all bricks/servers in a replica set to all in a volume to all in
the cluster. Unfortunately, that gets us nowhere in a two-server
two-brick cluster, which is very common especially in the critical case
of people trying GlusterFS for the first time and seeing how it responds
to failures. The other idea is arbiter nodes, which hold no data but
pump up the quorum number for the cluster (or for a volume if that’s how
we’re counting). Thus, if we have a volume on two nodes in a cluster
with more than two, a third node will be (automatically?) designated as
having an interest in that volume so that the effective quorum is two
out of three. Since tracking servers’ interests in volumes will already
have to be part of the second patch I’ve mentioned, adding an arbiter is
just a simple matter of manipulating that information so it should be a
pretty straightforward third patch.

Kind regards,

Jorick Astrego
Netbulae
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ovirt.org/pipermail/users/attachments/20140318/c98ee4e7/attachment-0001.html>