74 lines
2.9 KiB
ReStructuredText
74 lines
2.9 KiB
ReStructuredText
:title: Working with Volumes
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:description: How to create and share volumes
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:keywords: Examples, Usage, volume, docker, documentation, examples
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.. _volume_def:
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Data Volume
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===========
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.. versionadded:: v0.3.0
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Data volumes have been available since version 1 of the
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:doc:`../api/docker_remote_api`
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A *data volume* is a specially-designated directory within one or more
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containers that bypasses the :ref:`ufs_def` to provide several useful
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features for persistant or shared data:
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* **Data volumes can be shared and reused between containers.** This
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is the feature that makes data volumes so powerful. You can use it
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for anything from hot database upgrades to custom backup or
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replication tools. See the example below.
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* **Changes to a data volume are made directly**, without the overhead
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of a copy-on-write mechanism. This is good for very large files.
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* **Changes to a data volume will not be included at the next commit**
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because they are not recorded as regular filesystem changes in the
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top layer of the :ref:`ufs_def`
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Each container can have zero or more data volumes.
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Getting Started
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...............
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Using data volumes is as simple as adding a new flag: ``-v``. The parameter ``-v`` can be used more than once in order to create more volumes within the new container. The example below shows the instruction to create a container with two new volumes::
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docker run -v /var/volume1 -v /var/volume2 shykes/couchdb
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For a Dockerfile, the VOLUME instruction will add one or more new volumes to any container created from the image::
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VOLUME ["/var/volume1", "/var/volume2"]
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Create a new container using existing volumes from an existing container:
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---------------------------------------------------------------------------
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The command below creates a new container which is runnning as daemon ``-d`` and with one volume ``/var/lib/couchdb``::
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COUCH1=$(sudo docker run -d -v /var/lib/couchdb shykes/couchdb:2013-05-03)
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From the container id of that previous container ``$COUCH1`` it's possible to create new container sharing the same volume using the parameter ``-volumes-from container_id``::
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COUCH2=$(sudo docker run -d -volumes-from $COUCH1 shykes/couchdb:2013-05-03)
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Now, the second container has the all the information from the first volume.
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Create a new container which mounts a host directory into it:
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-------------------------------------------------------------
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-v=[]: Create a bind mount with: [host-dir]:[container-dir]:[rw|ro].
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If "host-dir" is missing, then docker creates a new volume.
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This is not available for a Dockerfile due the portability and sharing purpose of it. The [host-dir] volumes is something 100% host dependent and will break on any other machine.
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For example::
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sudo docker run -v /var/logs:/var/host_logs:ro shykes/couchdb:2013-05-03
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The command above mounts the host directory ``/var/logs`` into the container with read only permissions as ``/var/host_logs``.
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.. versionadded:: v0.5.0
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