just some additional info.current mechanical hard discs can not even fully utilize sata I(1.5gbps).only SSD can fully utilize sata II/sata III.also onboard raid implementation is inferior to dedicated raid cards & even software raid is considered as better by many compared to onboard raid.
*superuser.com/questions/313434/onboard-raid-vs-software-raid
*superuser.com/questions/313434/onboard-raid-vs-software-raid