[Gluster-users] HA replica

Ravishankar N ravishankar at redhat.com
Wed Mar 2 12:21:22 UTC 2016

On 02/18/2016 11:33 AM, Mike Stump wrote:
> On Feb 13, 2016, at 6:21 PM, Ravishankar N <ravishankar at redhat.com> wrote:
>> About the docs, could you list the links for client and server quorum where you found the details to be inadequate? I can't seem to find anything myself on readthedocs.:(
>> I'm anyway planning to do a detailed write up for arbiter volumes, split-brains, client and server quorums which can serve as a ready reckoner.
So I've made a write-up here: 
Hope this is more explanatory.

> So, http://www.gluster.org/community/documentation/index.php/GlusterFS_Concepts can explain that replica 2 is unlike RAID-1.  It can state that to achieve RAID-1, one must use replica 3.  http://gluster.readthedocs.org/en/latest/Administrator%20Guide/Setting%20Up%20Volumes/ likewise talks about high availability and replicated, but it could explain that replica 3 is required to achieve RAID-1.
> In
>    http://gluster.readthedocs.org/en/release-3.7.0/Features/server-quorum/
> it states:
>> Therefore, it is highly advisable to ensure that the cluster size is three or greater.
> So, I would have an easier time understanding this, is cluster size was linked to a definition.  Would my reading be correct if I read this as replica 3 or greater?
>> It need only be present to preserve the notion of a quorum majority less than the entire cluster membership, allowing the cluster to survive the loss of a single node without losing quorum.
> Again, here it talks about cluster membership.  I think I incorrectly viewed this as relating to the total list of peers rather than the replica count.
> 1 - https://en.wikipedia.org/wiki/Standard_RAID_levels
> 2 - https://btrfs.wiki.kernel.org/index.php/Using_Btrfs_with_Multiple_Devices

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