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add some info wrt backup and restore of volumes

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Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
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Sven Dowideit 2014-02-17 15:20:28 +10:00 committed by Sven Dowideit
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commit 5fde31ba9c
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docs/sources/use/working_with_volumes.rst
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@ -7,10 +7,6 @@
Share Directories via Volumes
=============================
.. versionadded:: v0.3.0
Data volumes have been available since version 1 of the
:doc:`../reference/api/docker_remote_api`
A *data volume* is a specially-designated directory within one or more
containers that bypasses the :ref:`ufs_def` to provide several useful
features for persistent or shared data:
@ -24,9 +20,15 @@ features for persistent or shared data:
* **Changes to a data volume will not be included at the next commit**
because they are not recorded as regular filesystem changes in the
top layer of the :ref:`ufs_def`
* **Volumes persist until no containers use them** as they are a reference
counted resource. The container does not need to be running to share its
volumes, but running it can help protect it against accidental removal
via ``docker rm``.
Each container can have zero or more data volumes.
.. versionadded:: v0.3.0
Getting Started
...............
@ -40,7 +42,7 @@ two new volumes::
This command will create the new container with two new volumes that
exits instantly (``true`` is pretty much the smallest, simplest program
that you can run). Once created you can mount its volumes in any other
container using the ``-volumes-from`` option; irrespecive of whether the
container using the ``-volumes-from`` option; irrespective of whether the
container is running or not.
Or, you can use the VOLUME instruction in a Dockerfile to add one or more new
@ -118,6 +120,38 @@ directories`` refer to directories in the ``boot2docker`` virtual machine, not t
Similarly, anytime when the docker daemon is on a remote machine, the ``host directories`` always refer to directories on the daemon's machine.
Backup, restore, or migrate data volumes
----------------------------------------
You cannot back up volumes using ``docker export``, ``docker save`` and ``docker cp``
because they are external to images.
Instead you can use ``--volumes-from`` to start a new container that can access the
data-container's volume. For example::
$ sudo docker run -rm --volumes-from DATA -v $(pwd):/backup busybox tar cvf /backup/backup.tar /data
* ``-rm`` - remove the container when it exits
* ``--volumes-from DATA`` - attach to the volumes shared by the ``DATA`` container
* ``-v $(pwd):/backup`` - bind mount the current directory into the container; to write the tar file to
* ``busybox`` - a small simpler image - good for quick maintenance
* ``tar cvf /backup/backup.tar /data`` - creates an uncompressed tar file of all the files in the ``/data`` directory
Then to restore to the same container, or another that you've made elsewhere::
# create a new data container
$ sudo docker run -v /data -name DATA2 busybox true
# untar the backup files into the new container's data volume
$ sudo docker run -rm --volumes-from DATA2 -v $(pwd):/backup busybox tar xvf /backup/backup.tar
data/
data/sven.txt
# compare to the original container
$ sudo docker run -rm --volumes-from DATA -v `pwd`:/backup busybox ls /data
sven.txt
You can use the basic techniques above to automate backup, migration and restore
testing using your preferred tools.
Known Issues
............