I have an Aurora R5 that came installed with a 256GB SSD (C drive) and a 1 TB HDD (D drive). I recently added a third drive, a Samsung 860 EVO SSD (F drive). I noticed that my Intel RST was not running so I reinstalled it from support before reading about ACHI drivers. In my BIOS the drives are set to RAID. Should I change it to AHCI, because from what I read SSD do better set to AHCI. How do I do this without a complete reinstall? Everything seems to be working right now.
My theory is that because Optane is a BTO option that requires Intel RST drivers, Dell ships all systems with RAID on in the BIOS even if your system doesn't actually have a RAID array configured or Optane installed.
Unless your system actually takes advantage of either raid based technologies, it's best to keep things set to AHCI because RST drivers can do weird crap sometimes.