I have a single cache drive that is indeed formatted in btrfs, and that acts as storage for appdata, docker image file etc.
My incomplete/complete folder is in my array though, but that shouldn't cause such a problem should it? It definately begins to choke up when I have active torrents downloading, but I don't have a speedy connection so the usage is around 4MB/s~.
And thanks for that repo, I'll give it a shot. Cheers binhex