Switch RAID to AHCI without reinstalling Windows 10

There is actually another way around this. Before you begin, make sure you remember your PC password (not PIN), or else you would be stuck in safe mode forever (with this way of entering safe mode).

Booting into Safe Mode will work even though the storage mode has been changed... Windows will notice the change and load the correct driver on the next normal boot. Basically that means, you can do this:

1. Run cmd as administrator (not PowerShell, you would have to escape {...})

2. Copy-paste this command, which will start Windows in Safe Mode the next time you reboot:

    bcdedit /set {current} safeboot minimal
   

3. Restart the computer and enter UEFI/BIOS setup.

4. Change the SATA operation mode from RAID to AHCI.

5. Save changes and exit Setup and Windows will automatically boot to Safe Mode.

6. Launch cmd again, as in step #1.

7. Copy-paste this command, which will start Windows in Normal Mode the next time you reboot:

    bcdedit /deletevalue {current} safeboot
   

8. Reboot and Windows will automatically start with AHCI drivers enabled.

You need to install the correct driver for your AHCI storage controller before changing the mode in the BIOS.

If you don't do so, after switching the mode Windows cannot load the storage controller driver needed to access the boot volume. Because this driver is loaded before the Plug and Play Manager, Windows can't automatically detect or otherwise search for the correct driver.

Pre-installing the driver should solve this.

That said, you don't mention the reason you want to do this, but if it's for reason of performance, in my experience there's no difference between the two modes on Dell XPS machines.