title: Confused about the numer of voting members in a MongoDB replica set?
body: <p>In the <a href="http://docs.mongodb.org/manual/core/replica-set-architectures/" rel="nofollow">replica set architecture</a> article the suggested (minimum) configuration is made of: one primary member and two secondary ones (or one secondary and a lightweight arbiter). Hence <strong>two voting members</strong>. </p>
  
  <p>However few lines below you can read (this is for having "smooth elections"):</p>
  
  <blockquote>
    <p>When adding additional members, ensure the following architectural
    conditions are true:</p>
    
    <ul>
    <li><p>The set has an odd number of voting members.</p>
    
    <p>If you have an even number of voting members, deploy an arbiter to create an odd number.</p></li>
    </ul>
  </blockquote>
  
  <p>If I'm right <strong>two is even</strong>, that is the suggested minimal configuration is wrong! How an even number of voters can cause elections that are "not smooth"? What's "not smooth" in terms of voting in the replica?</p>
  
  <p>More on this: even counting the primary as voter (thus three voters, odd number) if the primary goes down you'll end up with two voters. How the primary can vote if it's down? </p>