macos - Why is docker reporting 100% disk usage on a fresh ubuntu image?

I am no longer able to use docker or effectively run new images -- it is reporting that I have 100% disk usage. Here, you can see I am launching a pristine copy of ubuntu, and yet it is telling me I have no disk space left:

$ docker run -t -i ubuntu /bin/bash
root@3838b70bd76e:/# df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs           19G   18G     0 100% /
none             19G   18G     0 100% /
tmpfs          1005M     0 1005M   0% /dev
shm              64M     0   64M   0% /dev/shm
/dev/sda1        19G   18G     0 100% /etc/hosts
tmpfs          1005M     0 1005M   0% /proc/kcore

Separately, I am trying to start a mysql instance and it is giving me error messages that I believe are connected to the fact that I have no available disk. When I try to run orchardup/mysql, I get:

ERROR: 1030  Got error 28 from storage engine

Which means it has run out of storage space.

Given this, how should I interpret the above df -h report, and how can I determine what is consuming 100% of my disk? I am running docker 1.3, running on OSX 10.9.4, using boot2docker.

Thanks.

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Edit: As a workaround, I have run boot2docker delete, and then boot2docker init, and it appears to have trashed all of my images (fortunately I can rebuild them with my dockerfiles). Now, when I start a fresh ubuntu image:

root@f53d637e3d33:/# df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs           19G  373M   17G   3% /
none             19G  373M   17G   3% /
tmpfs          1005M     0 1005M   0% /dev
shm              64M     0   64M   0% /dev/shm
/dev/sda1        19G  373M   17G   3% /etc/hosts
tmpfs          1005M     0 1005M   0% /proc/kcore

So much better. But, I am still confused, there must be some kind of shared global disk across all images hosted by boot2docker that previously got filled up?

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Edit 2: I just downloaded a bunch of images, and now here is what I see when I run the ubuntu image and check free disk space:

root@f53d637e3d33:/# df -h
Filesystem      Size  Used Avail Use% Mounted on
rootfs           19G  2.7G   15G  16% /
none             19G  2.7G   15G  16% /
tmpfs          1005M     0 1005M   0% /dev
shm              64M     0   64M   0% /dev/shm
/dev/sda1        19G  2.7G   15G  16% /etc/hosts
tmpfs          1005M     0 1005M   0% /proc/kcore

From 3% to 16% consumed! Clearly there is some kind of shared disk between all of my images that I am not understanding...