I have an alienware 15 R2. It has a 256GB mSATA SSD and a 1 TB HDD. The laptop came with Windows 10 installed in RAID mode with Intel RST. The OS is installed on the SSD. Is there a way to disable RST and still be able to boot in the same OS?

Changing RAID SATA mode to AHCI in BIOS gives INACCESSIBLE_BOOT_DEVICE error. I am trying to dual-boot Ubuntu and disabling IRST will make life much easier.