Yes, you can set up a software RAID in FreeNAS between any two drives. Normally, it's not recommended to mix and match speeds for performance reasons. 5400RPM vs. 5900RPM isn't going to be a problem though.
Hi mfenn, i need help if you can. I setup my server and this mb BIOSTAR TH67B, the sata3 port is not work under Freenas, but the other 4 sata2 port are fine. Is there any bug in Freenas 8 that can not use sata3? I test the sata3 port by installing Windows 7 and it worked. I might have to install whs 2011, but I already move 1.5 tb of movies and other data on my freenas server.
Thank you.