Switched from Tixati to qBittorrent for BTN support since my nas has been leeched by a list of datacenter IPs.

Then I noticed that qbittorrent failed to write any file. After some digging, it turns out the C lib failed to do `file_mmap`. I'm using unraid and it offers both 9p and virtiofs to mount shares to vm. I though I'm using virtiofs, but it's actually 9p. The 9p mode failed to support mmap and the read performance is slow. With my ZFS setup, it can only read 60MB/s.

After switching to virtiofs, the read performance is back to normal, reaching about 700MB/s and mmap is working out of box.

I think unraid should really make the virtiofs as the first option, instead of 9p.