title: How to write specific rows to specific RegionServer?
body: <p>I have two region servers, <code>RS1</code> and <code>RS2</code>. I want to ensure that all the rows with key starting with letter less than <code>M</code> go to regions in <code>RS1</code> and then rest into regions in <code>RS2</code>.</p>
  
  <p>How to do it?</p>