FAQ
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 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 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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postedAug 11, '15 at 7:47a
activeAug 11, '15 at 11:17a
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