title: Running two instances of MongoDB
body: <p>I am working on a highly I/O Intensive application (A selection based on the availability of seats) using MERN Stack. 
  The app is expected to get 2000 concurrent users.
  I want to know whether it's wise to use two instances of MongoDB, one on the RAM (in memory) and another on the Hard drive. </p>
  
  <p>The RAM one to be used to store the available seats.
  And the Hard drive one to backup the data after regular intervals.
  But at the same time I know that if the server crashes my MongoDB data on the RAM is lost.</p>
  
  <p>Could anyone guide me please?</p>
  
  <p>I am using Socket IO instead of AJAX...</p>