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From Kaushal Shriyan <kaushalshri...@gmail.com>
Subject Re: Odd Number of Nodes spread across 3 Datacenter
Date Tue, 11 Aug 2015 11:07:05 GMT
Hi,

While referring to
http://whilefalse.blogspot.com.es/2012/12/building-global-highly-available.html
and the description "ZooKeeper requires a majority (n/2 + 1) of servers to
be available and able to communicate with each other in order to form a
quorum" I suppose it is floor function and not ceiling function while
referring to
https://en.wikipedia.org/wiki/Floor_and_ceiling_functions#Examples. Please
correct me if i am understanding it wrong?

Regards,

Kaushal

On Tue, 11 Aug 2015 at 14:31 Flavio Junqueira <fpj@apache.org> wrote:

> I don't think there is a straightforward answer to the question, but here
> is some insight.
>
> If you use 3 servers with 3 data centers, you'll have one server per DC,
> which means that upon a crash, the clients in some data center will have to
> go remotely for reads.
>
> With 5 servers, at least one DC will have at most one server, which is a
> bit better, but the DC with one server will have the problem that with the
> one server crashing, the clients will need to go remotely for reads.
>
> 7 or 9 are better options, since you can have multiple nodes per DC to
> serve local read traffic.
>
> I have used 5-7 per DC with flexible quorums in a system I worked on.
>
> -Flavio
>
> > On 11 Aug 2015, at 08:47, Kaushal Shriyan <kaushalshriyan@gmail.com>
> wrote:
> >
> > Hi,
> >
> > I have a very basic question of setting up Zookeeper ensemble across 3
> > Datacenter. Since zookeeper quorum is based on odd number of nodes for
> > Leader election. What would be the ideal odd number of nodes spread
> across
> > 3 Datacenter is it 3 or 5 or 7 or 9? if either of DC1 or DC2 or DC3 is
> not
> > reachable or degraded?
> >
> > DC1 meaning Datacenter 1
> > DC2 meaning Datacenter 2
> > DC3 meaning Datacenter 3
> >
> > Any help will be highly appreciable.
> >
> > Regards,
> >
> > Kaushal
>
>

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