We're using device-mapper thin provisioning technology. Same copy-on-write capabilities, but more compatible with upstream kernel versions
My main question is whether this will require users to create a fixed-size filesystem for each container up front, like you would have to do if you were using LVM snapshots directly.
The best place to follow progress on this is to track docker-dev (https://groups.google.com/forum/#!forum/docker-dev) and the #docker-dev irc channel.
- it will be thinly provisioned (i.e. it can be 10G or 100G but still use only a few MB on disk if it's essentially empty, like a sparse file), - it can be grown easily.
On the one hand, it's a bit less convenient because you have to care about the disk usage.
On the other hand, it's great because a single container can't eat up all your precious disk space (and if you want to run some public/semi-public stuff that's quasi mandatory).
If you want to check the current code, you can look here: https://github.com/alexlarsson/docker/tree/device-mapper3