I've recently used FreeNAS to test a new Filesserver. Here are some notes, which where hard to find online.
Installing FreeNAS on a USB-Stick
FreeNAS has some ready-made Images on their download page which are listed as:
This release, installed on an hard drive or on a flash device, use a RAM drive (like the LiveCD) for limiting access to a flash devise.
The problem is: there's no note that the images are gzipped and you cannot simply dd them to an USB-Stick and epect them to work. So you have to use a command like this to write the image to your USB-Stick:
gunzip -c ./FreeNAS-xxx.img | dd of=/dev/sdX
Where xxx is the version of the FreeNAS image and X is the number to identify the device where your USB-Stick is attached.