FreeNAS is awesome. FreeNAS can and will run as a VM. That does not make it a good idea.
Please do not run FreeNAS in production as a Virtual Machine!
- FreeNAS is designed to run on bare metal, without any clever storage systems (UNIX/VMFS filesystem layers, RAID card caches, etc!) getting in the way. Think about this: ZFS is designed to implement the functionality of a RAID controller. However, its cache is your system's RAM, and its processor is your system's CPU, both of which are probably a lot larger and faster than your hardware RAID...
Please do not run FreeNAS in production as a Virtual Machine!