Docker Cookbook

See Also
• Documentation of 
docker=py
• Docker article on HTTPS 
support
4.12 Changing the Storage Driver
Problem
You would like to use a different storage driver than the default used on your system
during Docker installation.
Solution
This recipe illustrates how to change the storage backend used by Docker. You will
start from a Ubuntu 14.04 installation with a 3.13 kernel and a Docker 1.7 setup with
Another Union File System (AUFS), and you will switch to the overlay filesystem. As
before, you can grab a Vagrantfile from the repository that comes with this book. Let’s
do it:
$ git clone https://github.com/how2dock/docbook.git
$ cd docbook/ch04/overlay
$ vagrant up
$ vagrant ssh
$ uname -r
3.13.0-39-generic
126 | Chapter 4: Docker Configuration and Development

---

$ docker info | grep Storage
Storage Driver: aufs
$ docker version | grep Server
Server version: 1.7.0
The overlay filesystem is available in the Linux kernel starting with 3.18. Therefore to
switch storage backends, you first need to 
upgrade
the kernel of your machine to 3.8
and restart:
$ cd /tmp
$ wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-vivid/\
linux-headers-3.18.0-031800-generic_3.18.0-031800.201412071935_amd64.deb
$ wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-vivid/\
linux-headers-3.18.0-031800_3.18.0-031800.201412071935_all.deb
$ wget http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.18-vivid/\
linux-image-3.18.0-031800-generic_3.18.0-031800.201412071935_amd64.deb
$ sudo dpkg -i linux-headers-3.18.0-*.deb linux-image-3.18.0-*.deb
$ sudo update-grub
$ sudo shutdown -r now
Once the machine has restarted, connect to it again. You can now edit the Docker
configuration file and specify Overlay as a storage driver by using the 
-s
option in
starting the Docker daemon:
$ uname -r
3.18.0-031800-generic
$ sudo su
# service docker stop
# echo DOCKER_OPTS=\"-s overlay\" >> /etc/default/docker
# service docker start
You now switch the storage backend for Docker:
$ docker info | grep Storage
Storage Driver: overlay
AUFS has been the default storage backend for 3.13–3.16 kernels,
especially on Ubuntu systems. Overlay is now in the upstream ker‐
nel starting with 3.18, and AUFS is not available. Consider switch‐
ing to Overlay.
Discussion
Docker can use multiple storage backends to store images and container filesystems.
The storage abstraction in Docker tries to minimize the space used by images and
container filesystems by keeping them in layers and tracking only the modifications
from layer to layer. It relies on union-based filesystems to accomplish this.
You can choose between the following storage backends: