how to install operating system on msata??

good day sirs,

i have a alienware 17 laptop and one of my hdd broke then i replaced with new one then configure it ti raid 0. using boot start up on LEGACY. and its working fine. i noticed that my msata is showing on my computer with nothing inside. i know that it supposed to have the OS on it but nothing.

here is the problem i tried to switch it back to UEFI secured boot but it cant detect my msata for booting. then also i revert it back to LEGACY then tried to install my operating system which is windows 8.1 but i cant it say something about GPT format or something. im newbie to this thing. anyone who can help me install back my OS to msata for ssd booting so i can put it back to UEFI secured boot. and  also how to make the UEFI detect my intel msata 80gb ssd.

thanks in advance

alienware 17,gtx 770 3gb, 1.5TB HHD, 80 gb msata 16gb RAM