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From Flavio Junqueira <...@apache.org>
Subject Re: Odd Number of Nodes spread across 3 Datacenter
Date Tue, 11 Aug 2015 09:00:49 GMT
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. 


> 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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