title: How to clean up /var/lib/docker/vfs directory
body: <p>I am trying to figure out how I can reclaim some of my disk space from Docker. 
  My /var/lib/docker directory currently looks like:</p>
  
  <pre><code>42M     containers
  3.6G    devicemapper
  14M     image
  68K     network
  20K     plugins
  4.0K    swarm
  4.0K    tmp
  4.0K    trust
  9.0G    vfs
  28K     volumes
  </code></pre>
  
  <p>I dont know why my vfs directory is so huge nor how to clean it up! My newer installations of docker on other servers dont even have this directory, so is it safe to delete?</p>
  
  <p>I am running docker 1.13.1, using the devicemapper storage driver on an Ubuntu 14.04 server. This docker has been upgraded several times in the past. I am only running 3 containers on it and most of the important volumes are mounted to the host. </p>
  
  <p>I've run "docker system prune" but it reclaims nothing. I've also cleaned out all the images I dont need. </p>