[Gluster-devel] [Gluster-users] Proposal for GlusterD-2.0

[Jonathan Barber]

On 8 September 2014 05:05, Krishnan Parthasarathi <kparthas at redhat.com>
wrote:

>
>
> > Bulk of current GlusterD code deals with keeping the configuration of the
> > cluster and the volumes in it consistent and available across the nodes.
> The
> > current algorithm is not scalable (N^2 in no. of nodes) and doesn't
> prevent
> > split-brain of configuration. This is the problem area we are targeting
> for
> > the first phase.
> >
> > As part of the first phase, we aim to delegate the distributed
> configuration
> > store. We are exploring consul [1] as a replacement for the existing
> > distributed configuration store (sum total of /var/lib/glusterd/* across
> all
> > nodes). Consul provides distributed configuration store which is
> consistent
> > and partition tolerant. By moving all Gluster related configuration
> > information into consul we could avoid split-brain situations.
> > Did you get a chance to go over the following questions while making the
> > decision? If yes could you please share the info.
> > What are the consistency guarantees for changing the configuration in
> case of
> > network partitions?
> > specifically when there are 2 nodes and 1 of them is not reachable?
> > consistency guarantees when there are more than 2 nodes?
> > What are the consistency guarantees for reading configuration in case of
> > network partitions?
>
> consul uses Raft[1] distributed consensus algorithm internally for
> maintaining
> consistency. The Raft consensus algorithm is proven to be correct. I will
> be
> going through the workings of the algorithm soon. I will share my answers
> to
> the above questions after that. Thanks for the questions, it is important
> for the user to understand the behaviour of a system especially under
> failure.
> I am considering adding a FAQ section to this proposal, where questions
> like the above would
> go, once it gets accepted and makes it to the feature page.
>
> [1] -
> https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf
>
>
The following article provides some results on how Consul works following
partitioning, actually testing whether it recovers successfully:
http://aphyr.com/posts/316-call-me-maybe-etcd-and-consul

It gives Consul a positive review.

HTH

~KP
>
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-- 
Jonathan Barber <jonathan.barber at gmail.com>
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