FreeNAS is not a Linux distribution. It is build from FreeBSD. It’s stable version 0.68 is rock and very easy to setup. I have tried the beta version 0.685b but unsuccessfully setting it up. It also supports RAID.
Dated on 2007-07-21 :
I updated the firmware from 0.68 to 0.685b1 without any problem. Be keep in mind that you should install embedded option of 0.68.