If you’re looking for just filesharing capabilities, OwnCloud might be a good alternative. It’s recently been rewritten in Go and its supposedly quite fast. I must say that I haven’t used it myself.

Another alternative could be Nextcloud, but that comes with a whole suite of other software such as calendar, contacts, …

I’ve also heard some good things about seafile, but never used it myself either.

I personally use a script which stops all containers, rsyncs the bind mounts (normal folders on the filesystem) and then restarts them. It runs every night so it isn’t a problem that services are down for a few minutes.

Ideally, you would also make a database dump instead of just backing up the bind mounts.