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.