Why use a docker volume? Seems like a good way to accidentally lose your files. Just volume-mount from the external filesystem and back it up the same way you would any linux application's files - maybe stop it, maybe not, depends on how it uses files.
It's nice to be able to survive someone purging Docker by accident, and it's nice to know `/wherever/you/like` is where your files are instead of in `/var/lib/containers/some long hash/`
