XPS 8940, AHCI vs. RAID

Question

My Dell 8940 was equipped originally with M.2 (2280) NVME 256 GB SSD and 1 TB SATA HDD.

In BIOS the SATA operation was by default set RAID. Reading many articles regarding the proper replacement of SSD and restoring the cloned image of operating system to new SSD drive some have been recommending prior to cloning process to change from RAID to AHCI. The reason that AHCI mode was preferrred ( but not mandatory ! ) because the operating system can not "see" storage device connected behind a RAID controller unles proper driver is installed. Is that so ? Why then does Dell keep in the machine SATA operation for RAID ? Some sources state since SSD has PCIe connection factor not SATA that requirement for setup as AHCI is unnecessary requirement.

Does XPS 8940 machine have those "proper" drivers ?

redxps630 · Answer

Dell keeps SATA Operation in 'RAID On' mode by default for better performance with Intel Rapid Storage Technology (IRST), unified driver management, and compatibility with Intel Optane memory, even for single SSD setups, because the specialized IRST driver offers higher speeds than Windows' native AHCI driver, though AHCI is the standard for basic single-drive setups. This 'RAID On' setting allows Intel's advanced drivers to manage the drive for optimal speed, making it a factory standard for modern systems.

RogerXY · Answer

@redxps630​  I would agree if my machine would have SSD with form factors 2.5' or M.2 that has SATA interface and requires AHCI protocol but I have a single SSD with PCIe interface that uses NVMe protocol. Perhaps, Dell wanted to advance this machine with two HDD's besides one SSD...

redxps630 · Answer

For most modern systems installing Windows 10/11,

you generally don't need Intel Rapid Storage Technology (IRST) for a standard NVMe SSD; Windows has built-in drivers, and IRST is mainly for Intel RAID setups. You only need to load the IRST driver (specifically the VMD controller driver) during OS installation if the installer doesn't see the drive, which usually happens when the BIOS is set to RAID instead of AHCI, or on certain newer Intel platforms (11th-14th Gen).

https://www.dell.com/support/kbdoc/en-us/000188116/intel-11th-generation-processors-no-drives-can-be-found-during-windows-10-installation

redxps630 · Answer

an NVMe SSD generally uses built-in Windows drivers (like the standard NVMe driver in Win 10/11) for basic function, but you often need specific drivers, like Intel's

IRST (Rapid Storage Technology) for newer Intel platforms (VMD), or manufacturer drivers (Samsung, Crucial) for optimal performance, management, and detection during OS installs, especially if the generic driver fails.

If Windows setup doesn't see the NVMe drive, especially on newer Intel systems (11th Gen+), you need the IRST (Intel Rapid Storage Technology) driver preloaded.

XPS Desktops

XPS 8940, AHCI vs. RAID

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