title: requirement of 3 journal nodes in HA hadoop setup
body: <p>I am quite new to hadoop. As i am setting up a hadoop namenode ha using qoroum journal manager, i am a bit confused on the requirements. The official documentations on apache site says </p>
  
  <blockquote>
    <p>Note: There must be at least 3 JournalNode daemons, since edit log modifications must be written to a majority of JNs.</p>
  </blockquote>
  
  <p>what does this means? why do we need 3 journal-nodes instead of two? </p>