How to analyze disk usage of a Docker container

Question

I can see that Docker takes 12GB of my filesystem:

2.7G    /var/lib/docker/vfs/dir
2.7G    /var/lib/docker/vfs
2.8G    /var/lib/docker/devicemapper/mnt
6.3G    /var/lib/docker/devicemapper/devicemapper
9.1G    /var/lib/docker/devicemapper
12G     /var/lib/docker

But, how do I know how this is distributed over the containers?

I tried to attach to the containers by running (the new v1.3 command)

docker exec -it <container_name> bash

and then running 'df -h' to analyze the disk usage. It seems to be working, but not with containers that use 'volumes-from'.

For example, I use a data-only container for MongoDB, called 'mongo-data'.

When I run docker run -it --volumes-from mongo-data busybox, and then df -h inside the container, It says that the filesystem mounted on /data/db (my 'mongo-data' data-only container) uses 11.3G, but when I do du -h /data/db, it says that it uses only 2.1G.

So, how do I analyze a container/volume disk usage? Or, in my case, how do I find out the 'mongo-data' container size?

Answer 1

You can use

docker history IMAGE_ID

to see how the image size is ditributed between its various sub-components.

Answer 2

The volume part did not work anymore so if anyone is insterested I just change the above script a little bit:

for d in `docker ps | awk '{print $1}' | tail -n +2`; do
    d_name=`docker inspect -f {{.Name}} $d`
    echo "========================================================="
    echo "$d_name ($d) container size:"
    sudo du -d 2 -h /var/lib/docker/aufs | grep `docker inspect -f "{{.Id}}" $d`
    echo "$d_name ($d) volumes:"
    for mount in `docker inspect -f "{{range .Mounts}} {{.Source}}:{{.Destination}}                                                                                                                                                      
    {{end}}" $d`; do
        size=`echo $mount | cut -d':' -f1 | sudo xargs du -d 0 -h`
        mnt=`echo $mount | cut -d':' -f2`
        echo "$size mounted on $mnt"
    done
done

Answer 3

Improving Maxime's anwser:

docker ps --size

You'll see something like this:

+---------------+---------------+--------------------+
| CONTAINER ID  | IMAGE         | SIZE               |
+===============+===============+====================+
| 6ca0cef8db8d  | nginx         | 2B (virtual 183MB) |
| 3ab1a4d8dc5a  | nginx         | 5B (virtual 183MB) |
+---------------+---------------+--------------------+

When starting a container, the image that the container is started from is mounted read-only (virtual).
On top of that, a writable layer is mounted, in which any changes made to the container are written.

So the Virtual size (183MB in the example) is used only once, irregardless of how many containers are started from the same image - I can start 1 container or a thousand; no extra disk space is used.
The "Size" (2B in the example) is unique per container though, so the total space used on disk is:

183MB + 5B + 2B

Be aware that the size shown does not include all disk space used for a container.
Things that are not included currently are;
- volumes
- swapping
- checkpoints
- disk space used for log-files generated by container

https://github.com/docker/docker.github.io/issues/1520#issuecomment-305179362

Answer 4

After 1.13.0, Docker includes a new command docker system df to show docker disk usage.

$ docker system df
TYPE            TOTAL        ACTIVE     SIZE        RECLAIMABLE
Images          5            1          2.777 GB    2.647 GB (95%)
Containers      1            1          0 B         0B
Local Volumes   4            1          3.207 GB    2.261 (70%)

To show more detailed information on space usage:

$ docker system df --verbose

Answer 5

If you want to reduce the size of many-layered images, I can recommend Jason Wilder's docker-squash utility. Get it from GitHub here: https://github.com/jwilder/docker-squash

Answer 6

Posting this as an answer because my comments above got hidden:

List the size of a container:

du -d 2 -h /var/lib/docker/devicemapper | grep `docker inspect -f "{{.Id}}" <container_name>`

List the sizes of a container's volumes:

docker inspect -f "{{.Volumes}}" <container_name> | sed 's/map\[//' | sed 's/]//' | tr ' ' '\n' | sed 's/.*://' | xargs sudo du -d 1 -h

Edit: List all running containers' sizes and volumes:

for d in `docker ps -q`; do
    d_name=`docker inspect -f {{.Name}} $d`
    echo "========================================================="
    echo "$d_name ($d) container size:"
    sudo du -d 2 -h /var/lib/docker/devicemapper | grep `docker inspect -f "{{.Id}}" $d`
    echo "$d_name ($d) volumes:"
    docker inspect -f "{{.Volumes}}" $d | sed 's/map\[//' | sed 's/]//' | tr ' ' '\n' | sed 's/.*://' | xargs sudo du -d 1 -h
done

NOTE: Change 'devicemapper' according to your Docker filesystem (e.g 'aufs')