Sorry to re-open the discussion again, but rutorrent is throwing me disk space errors and I'm unable to add new torrents.
I've confirmed (well, pretty sure at least) it's not a mount / nfs issue, as I can touch/rm files on the /mnt/... path as detailed above.
I can tell rutorrent to add a torrent to /mnt/downloads/ but it doesn't show up in the client. I also get the "Warning! The disk is full. rTorrent may not run correctly..." etc bubble in the bottom left. I disabled the diskspace plugin, but no change. I tried both / and /mnt as topdir in both the global and user specific configs, no change.
I did follow your steps above for the quota path changes, so I'm wondering if I've overlooked the obvious as to why it's reporting 0 bytes free. Also as requested output of lsblc and fstab