For optimal stability and preformance, it's best to use all identical drives in the array.

Thank you for the Info.

Can u use two hard drives that have different RPM speeds?

you can but you wont get he best performance speed.
it is better to use two drives that have the same RPM speed and the same transfer rate .

7200 rpm speed

data transfer rate -- sata 1.5 sata 3gb and sata 6gb
but some mother boards ( the older ones from a year ago ) dont have the sata 6gb on alot of the board, check you manual to see if your mother board has the sata 6gb transfer rate
if not sata 3gb is you best bet to use for hard drivers, you can use sata 6gb hard drives, But you will have a set back on the transfer speed rate, a bottle neck if you will.

to set up the raid configuration follow the manual for the best possible information it has to offer.

each drive will need to formated using the raid formate option, that is the only way to true set up a raid drive system.

other wise when you go to install your operating system on the drives, it will not allow to do so.

the drives have to formated with the raid set and drivers from you install disk for your mother board.

Hope this helps you out more.

When doing RAID 0 drives with be identical to insure compatibility, stability & performance.