Riak CS need for 5 servers?
shankar at opendrops.com
Fri Apr 3 14:24:25 EDT 2015
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. 
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?
On Fri, Apr 3, 2015 at 11:42 PM, Christopher Meiklejohn <
cmeiklejohn at basho.com> wrote:
> > On Apr 3, 2015, at 10:38 AM, Shankar Dhanasekaran <shankar at opendrops.com>
> > hi,
> > For the organization that I am working for, it seems like 25tb of
> storage is needed. Reading riak docs, it's mentioned that at least 5
> servers should be put in place.
> > what is the harm in having only 2 riak nodes? will this reduce
> performance? or cause loss of data? Since Riak is masterless, either one of
> the server will have the data at any point of time.
> If you have only two nodes and you incur one failure, you will no longer
> be able to write to a majority quorum , which means that a subsequent
> failure will result in potential unrecoverable data loss. This is why the
> official recommendation used to be 3 nodes.
> We’ve changed that to 5 nodes because this is the minimum amount of nodes
> needed to ensure all copies of each object are stored on different physical
> nodes. 
> - Chris
>  This assumes a default configuration with n_val = 3.
>  The partition / cluster claim algorithm attempts to ensure that all
> preference lists are on a disjoint set of nodes.
> Christopher Meiklejohn
> Senior Software Engineer
> Basho Technologies, Inc.
> cmeiklejohn at basho.com
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