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Docs: Improve description on volume removal

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A comment in https://github.com/docker/docker/issues/6354#issuecomment-74160215
brought to light that the "Managing Data in containers" section contained an
incorrect (or confusing) line;

  "Volumes persist until no containers use them"

Which implies that volumes are automatically removed if they are no longer
referenced by a container.

This pull-request attempts to add some information explaining that volumes are
never automatically removed by Docker and adds some extra hints on working
with data volumes.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
This commit is contained in:
Sebastiaan van Stijn 2015-02-13 01:17:33 +01:00
parent 99ca215c65
commit 00f2fd1dd5
1 changed files with 14 additions and 1 deletions
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15
docs/sources/userguide/dockervolumes.md
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@ -28,7 +28,12 @@ persistent or shared data:
- Data volumes can be shared and reused between containers
- Changes to a data volume are made directly
- Changes to a data volume will not be included when you update an image
- Volumes persist until no containers use them
- Data volumes persist even if the container itself is deleted
Data volumes are designed to persist data, independent of the container's life
cycle. Docker will therefore *never* automatically delete volumes when you remove
a container, nor will it "garbage collect" volumes that are no longer referenced
by a container.
### Adding a data volume
@ -141,6 +146,14 @@ be deleted. To delete the volume from disk, you must explicitly call
`docker rm -v` against the last container with a reference to the volume. This
allows you to upgrade, or effectively migrate data volumes between containers.
> **Note:** Docker will not warn you when removing a container *without*
> providing the `-v` option to delete its volumes. If you remove containers
> without using the `-v` option, you may end up with "dangling" volumes;
> volumes that are no longer referenced by a container.
> Dangling volumes are difficult to get rid of and can take up a large amount
> of disk space. We're working on improving volume management and you can check
> progress on this in [pull request #8484](https://github.com/docker/docker/pull/8484)
## Backup, restore, or migrate data volumes
Another useful function we can perform with volumes is use them for