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.
- 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
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.