Re: [Gluster-devel] [Gluster-users] Default quorum for 2 way replication
On 03/04/2016 10:05 PM, Diego Remolina wrote: 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. This is server side quorum. This is good. But what we are discussing here is for just 2 nodes, what should be the default. Pranith Diego On Fri, Mar 4, 2016 at 10:40 AM, Jeff Darcywrote: 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. ___ Gluster-users mailing list gluster-us...@gluster.org http://www.gluster.org/mailman/listinfo/gluster-users ___ Gluster-devel mailing list Gluster-devel@gluster.org http://www.gluster.org/mailman/listinfo/gluster-devel
Re: [Gluster-devel] [Gluster-users] Default quorum for 2 way replication
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. Diego On Fri, Mar 4, 2016 at 10:40 AM, Jeff Darcywrote: >> 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. > ___ > Gluster-users mailing list > gluster-us...@gluster.org > http://www.gluster.org/mailman/listinfo/gluster-users ___ Gluster-devel mailing list Gluster-devel@gluster.org http://www.gluster.org/mailman/listinfo/gluster-devel