This script removes orphaned folders from docker to reclaim space. I didn't write it, but I can't remember where I got it from; it was posted on one of the github issue logs for docker. I am posting it here so I don't lose it.

remove-docker-orphaned.py

#!/usr/bin/env python
"""
Check all existing Docker containers for their mapped paths, and then purge any
zombie directories in docker's volumes directory which don't correspond to an
existing container.

"""
# By using execfile(this_file, dict(__file__=this_file)) you will

this_file="/home/russosv/bin/env/bin/activate_this.py" 
execfile(this_file, dict(__file__=this_file))


import logging
import os
import sys
from shutil import rmtree

import docker


DOCKER_VOLUMES_DIR = "/var/lib/docker/vfs/dir"


def get_immediate_subdirectories(a_dir):
    return [os.path.join(a_dir, name) for name in os.listdir(a_dir)
            if os.path.isdir(os.path.join(a_dir, name))]


def main():
    logging.basicConfig(level=logging.INFO)

    client = docker.Client()

    valid_dirs = []
    for container in client.containers(all=True):
        volumes = client.inspect_container(container['Id'])['Volumes']
        if not volumes:
            continue

        for _, real_path in volumes.iteritems():
            if real_path.startswith(DOCKER_VOLUMES_DIR):
                valid_dirs.append(real_path)

    all_dirs = get_immediate_subdirectories(DOCKER_VOLUMES_DIR)
    invalid_dirs = set(all_dirs).difference(valid_dirs)

    logging.info("Purging %s dangling Docker volumes out of %s total volumes found.",
                 len(invalid_dirs), len(all_dirs))
    for invalid_dir in invalid_dirs:
        logging.info("Purging directory: %s", invalid_dir)
        rmtree(invalid_dir)

    logging.info("All done.")


if __name__ == "__main__":
    sys.exit(main())