Docker default images location

Prepare your new block storage, this will house the moved docker folder

# format the new block storage device
mkfs.ext4 /dev/sdx

# create a mount point
mkdir /mnt/diskX

# mount the file or do equivalent mount in /etc/fstab
mount /dev/sdx1 /mnt/diskX

# create a new folder to house docker
mkdir /mnt/diskX/docker
chmod 700 /mnt/diskX/docker

Setup the move

# stop containers and docker daemon
docker ps -q | xargs docker kill
service docker stop

# if devicemapper exists
cd /var/lib/docker/devicemapper/mnt
umount ./*

# mv didn't work with sudo, must be ROOT user - 
sudo bash
mv /var/lib/docker /mnt/diskX/docker

# set the flag in /etc/default/docker to
e.g. DOCKER_OPTS="--dns 8.8.8.8 --dns 8.8.4.4 -g /mnt/diskX/docker"

# restart docker daemon
sudo /etc/init.d/docker restart

Test that when you create a container the hash appears in /mnt/diskX/docker/containers