We built https://github.com/containership/codexd (based on our https://github.com/containership/node-btrfs module) which provides filesystem snapshots / restoration for btrfs. Additional filesystems such as ZFS will be supported in the future. If a user does not have one of the supported filesystems installed, tar archives will be used. This library is not yet merged into https://github.com/containership/containership.core, but once merged will provide the ability for persistent data to be moved between servers, if and when a container moves.
Data persistence is already fully functional in our hosted Cloud offering.