There is another problem of other than space. I grade programming assigments with Docker and let the students grade too, and when containers get too much, docker tries to read each of the metadata and it hangs, and I could not find the issue and could not remote reboot my server, so I walked to server room at 4 am. For a 8 core system, load avg was 33. So, be careful with your containers, remove them when not needed.