Should be able to switch back and forth, I have done that on my R10 without any issues. What's the boot error when it's set to AHCI?

The issue with RAID for NVME is that you cannot read the SMART attributes of the drive. At least not on my R10. Needs to be AHCI to read those.

I just tried it again and when switching in bios I get the following warning:

Warning! Changing this setting may prevent your operating system from booting or require a re-install.

When booting into Windows I get:

Your device ran into a problem and needs to restart.

This time it automatically started dell support assistant, I canceled. Windows was in some repair mode. I just canceled and eventually booted up. It clearly doesn't like me playing with this setting.

I guess I can re-install if I have to. Where do I get a re-install image?

It's said to RAID so the RAID driver is installed. You should be able to set to AHCI without any issues and switch between RAID and AHCI, as they don't have a RAID volume installed.

Just don't make a RAID volume, because then you will be loosing the ability to boot in AHCI mode. Normal volumes only.

As far as performance, you might need to run a TRIM on the SSD. It's a good idea to TRIM on a weekly basis, as performance loss occurs over time on an SSD due to the deleted blocks that occur over time.

Another thing with CrystalDiskMark is to set it to SSD testing mode, if you have not done so already.

Thanks for the reply.

CrystalDiskMark is set to SSD setting.

I tried to set the bios to AHCI and it wouldn't boot in Windows. I had to switch it back. I think I may need to re-install Windows for AHCI to work?

Found a way to enable it without a re-install. Seems to work, will post a link. Just testing again.

They do it because this way you can switch from Raid to AHCI. Switching from AHCI to RAID requires a lot more work.

I can't figure out any other reason why.

Found this link to switch without re-installing and it did work

https://superuser.com/questions/1280141/switch-raid-to-ahci-without-reinstalling-windows-10

And look at that:

Why would dell configure the bios this way. Can you even get raid on a R15?

Most users would never know they have an issue or where to look.

Another issue I had was the ram was configured for 4800mhz when I ordered 5200. I had to enable overclocking and reboot for it to work.

And this is why I always recommend not to run a desktop in RAID mode, as often it causes more issues than it' worth, especially with only a single disk installed in the system...