You actually have to set up the drives in RAID yourself. So it didn't.
1.) Check the boot order in your BIOS, you want your OS drive as first boot. It should, but doesn't have to be on the SATA port 0 or 1, depending on your mobo.
2.) Check the BIOS setting, that the SATA drives are in ACHI, not RAID or IDE Compatible.
3.) Boot into Windows.
Windows won't see the drive until it's formatted!
4.) Go into Disk Management and format the drive: Start/Computer/right-click/Manage/choose Disk Management on the left pane/right click the second drive you added/choose "New Simple Volume"/then format. I hope these steps are right