title: Understanding id_partition in Paperclip
body: <p>I'm using Paperclip to store audio files in AWS.</p>
  
  <p>The files path has an id_partition component (spanning 3 directories).</p>
  
  <p>How does this field is calculated?</p>
  
  <p>I want to be able to track the file from my rails module (or DB entry)</p>
  
  <p>Thank you</p>