* fh-update will not remove files from partial dirs if the files are
  removed from the partial file. To fix I'll need to store state in /var
* Need to stop the init script on halt too -- rc0 I think.
* Need cron.daily/weekly/monthly 0 and 99 scripts that mount and unmount
  the disk (optionally, where needed).
* The ondisk_dir could be marked immutable, or copied to a RO ramdisk,
  to prevent accidental writes to offline dirs.
