Problem: the BitTorrent client saves the active fragments to a directory on the internal HD, so my HD was about to get full as I am about a third of the way through the torrent. I can't find a setting to move this temp directory. I can set the folder where completed files go, I can set the folder where incomplete files go, but not the folder where actively fragments are cached, essentially meaning I can't process a torrent larger than about 2GB, which makes the whole torrent thing a bit useless.
So, being a Unix geek at heart, I decide to move the directory used by the client to an external HD and create a soft link using 'ln -s source target' so that the app just traverses the tree normally, but actually using the external HD.
Works fine, I have about 700GB available now for torrent processing. Sweet Unix Control.