This is more of a post for me to remember how to do this so its brief.
If you’ve come across this, and haven’t played around with FreeNAS, make sure you read the guides on the website before you try this.
- Download freenas 8 from freenas.org
- Burn Freenas 8 into a CD
- plug in a USB flash drive (1GB is sufficient)
- Start system from CD
- Pick option to install in HDD/USB
- Install onto USB
- Restart System
Start from USB
Setting up raid:
I have 2 WD 1TB SATA harddrives  in the system
- Go into storage
- Click Add Volume
- Give it a name
- Select both your harddrives
- select “ZFS” as file system (apparently its better)
- Select mirror
- Click Add Volume