I'm using FreeNAS 8.0.1Beta4 AMD64.
Once the USB drive is connected, I get the following message in the console:
"uhub_reattach_port: port 1 reset failed, error=USB_ERR_TIMEOUT uhub_reattach_port: device problem (USB_ERR_TIMEOUT), disabling port 1"
Thus, no device shows up in /dev for me to mount.