Those who use FreeNAS with virtual machines (I have e.g. the development environment for the blog theme in a Ubuntu VM) will want to use data from the NAS sooner or later. FreeNAS offers VT9P as a possibility here.
The Plan9 file system requires a few non-standard mount options. While it is easy to mount in the console, once you enter it in the fstab, it requires a more detailed entry. Works for my setup:
data /mnt/data 9p rw,sync,dirsync,relatime,trans=virtio,version=9p2000.L 0 0
This makes the volume "data", which is configured in FreeNAS, available on mount "/mnt/data" at boot time.