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? On Fri, Apr 3, 2015 at 11:42 PM, Christopher Meiklejohn < cmeiklej...@basho.com> wrote: > > > On Apr 3, 2015, at 10:38 AM, Shankar Dhanasekaran <shan...@opendrops.com> > wrote: > > > > 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 [1], 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. [2] > > - Chris > > [1] This assumes a default configuration with n_val = 3. > [2] 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. > cmeiklej...@basho.com > >
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