Yes, you can do this. I am assuming you plan to use the "built-in RAID" features of your motherboard. Look at the mobo manual carefully for instructions on how to set up a RAID array. I'm sure it will start out telling you how to access the RAID Management part of your mobo. When you go there, you will find that you must specify exactly which connected HDD's are to be used to create your new RAID array. Any that are NOT specifically allocated to the array (like, your old boot drive) are NOT part of the array and will continue to work as they always did.