disk.md

So, I can replicate this ballooning:

$ docker -v
Docker version 17.06.2-ce, build cec0b72

Here's the base image size after doing "Reset to factory defaults"

du -h /Users/curtis/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2
1.3G    /Users/curtis/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2

So 1.3GB is the size of the base VM. I then did a fresh chorus docker setup and checked docker disk usage

docker system df -v
Images space usage:

REPOSITORY                    TAG                 IMAGE ID            CREATED ago             SIZE                SHARED SIZE         UNIQUE SiZE         CONTAINERS
chorus_app                    latest              8dcc04c1df98        About an hour ago ago   2.212GB             815.3MB             1.397GB             0
voxmedia/docker_base_images   rails-0.3           97fde84706e4        11 days ago ago         815.3MB             815.3MB             0B                  0
nginx                         latest              b8efb18f159b        6 weeks ago ago         107.5MB             0B                  107.5MB             0
redis                         latest              d4f259423416        6 weeks ago ago         105.9MB             0B                  105.9MB             0
voxmedia/statsd-vis           latest              f9aa67167ff4        2 months ago ago        108.5MB             0B                  108.5MB             0
eugenmayer/unison             hostsync_0.2        50c4b94687aa        4 months ago ago        79.78MB             0B                  79.78MB             0
elasticsearch                 1.7.5               8497e1a8039b        10 months ago ago       347MB               0B                  347MB               0
mdsol/docker-ssh-exec         latest              3482bf17ad0d        14 months ago ago       4.343MB             0B                  4.343MB             1
mysql                         5.5.49              2f94d2a2ac89        15 months ago ago       255.9MB             0B                  255.9MB             0
memcached                     1.4.24              66438aa20444        22 months ago ago       132.2MB             0B                  132.2MB             0

Containers space usage:

CONTAINER ID        IMAGE                   COMMAND                  LOCAL VOLUMES       SIZE                CREATED ago             STATUS              NAMES
f3f0284e9679        mdsol/docker-ssh-exec   "/docker-ssh-exec ..."   0                   0B                  About an hour ago ago   Up 14 minutes       docker-ssh-exec

Local Volumes space usage:

VOLUME NAME                                                        LINKS               SIZE
chorus_bundle                                                      0                   399.5MB
chorus_mysql-data                                                  0                   2.128GB
2a9957cfd0db892af6b3beff798e4d057430f915bc3b33353811b8703b0c651d   0                   0B
3596f912e609e720d06452c9210ff316d836bf41dc7918052e1d4bc498656366   0                   109B
7c79f7eced1cc452f0d618f140b7df097ebadb707f4ed771279c79f72b223159   0                   157B
chorus-sync                                                        0                   868.9MB

Which ends up totally 5.93GB.

Checked the VM image again

9.2G    /Users/curtis/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/Docker.qcow2

So 9.2 - 5.93 (reported docker usage) - 1.3 (base image size) = 1.97GB overhead.

2GB overhead seems pretty reasonable to me.