title: RethinkDB shards & replicas vs MongoDB shards & replicas sets
body: <p>In MongoDB,  when you want to let say have a 3 shards with replica-sets, you end up needing, for production use, a minumum of 7 servers (2 per shard for high-availability + 1 arbitrer at least).</p>
  
  <p>In RethinkDB, I can't find some equivalent or good sugestions, in terms of cluster architecture &amp; design.</p>
  
  <p>Any help is welcome.</p>