[Gluster-users] [Gluster-devel] Default quorum for 2 way replication

Diego Remolina dijuremo at gmail.com
Fri Mar 4 16:35:51 UTC 2016

I run a few two node glusterfs instances, but always have a third
machine acting as an arbiter. I am with Jeff on this one, better safe
than sorry.

Setting up a 3rd system without bricks to achieve quorum is very easy.


On Fri, Mar 4, 2016 at 10:40 AM, Jeff Darcy <jdarcy at redhat.com> wrote:
>> I like the default to be 'none'. Reason: If we have 'auto' as quorum for
>> 2-way replication and first brick dies, there is no HA. If users are
>> fine with it, it is better to use plain distribute volume
> "Availability" is a tricky word.  Does it mean access to data now, or
> later despite failure?  Taking a volume down due to loss of quorum might
> be equivalent to having no replication in the first sense, but certainly
> not in the second.  When the possibility (likelihood?) of split brain is
> considered, enforcing quorum actually does a *better* job of preserving
> availability in the second sense.  I believe this second sense is most
> often what users care about, and therefore quorum enforcement should be
> the default.
> I think we all agree that quorum is a bit slippery when N=2.  That's
> where there really is a tradeoff between (immediate) availability and
> (highest levels of) data integrity.  That's why arbiters showed up first
> in the NSR specs, and later in AFR.  We should definitely try to push
> people toward N>=3 as much as we can.  However, the ability to "scale
> down" is one of the things that differentiate us vs. both our Ceph
> cousins and our true competitors.  Many of our users will stop at N=2 no
> matter what we say.  However unwise that might be, we must still do what
> we can to minimize harm when things go awry.
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