Riak CS need for 5 servers?

Christopher Meiklejohn cmeiklejohn at basho.com
Fri Apr 3 14:29:21 EDT 2015

> On Apr 3, 2015, at 11:24 AM, Shankar Dhanasekaran <shankar at opendrops.com> wrote:
> Thanks Chris for your answer. I still don't comprehend what is meant by 
> this is the minimum amount of nodes needed to ensure all copies of each object are stored on different physical nodes. [2]
> Why can't a 3 node cluster store the data in each of them? I am reading the little riak book as well but still I don't understand what is the magic value of 5?

Five is the minimum number of nodes required to guarantee each copy of each object is not stored on the same physical machine.  With three this can not be guaranteed, so you might have two copies (out of three) for a given object on the same machine.

It’s an optimization problem computed during node membership referred to as “claim.”

[1] http://lists.basho.com/pipermail/riak-users_lists.basho.com/2011-February/003319.html
[2] http://basho.com/why-your-riak-cluster-should-have-at-least-five-nodes/

Christopher Meiklejohn
Senior Software Engineer
Basho Technologies, Inc.
cmeiklejohn at basho.com

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