XPS 8940, Samsung EVO 970 Plus, slow performance

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Yes, I'm using the 970 Evo Plus and it's working fine.  What driver are you using?  I performed a clean install just to make sure all worked well.

I have also done a clean install then installed the Samsung NVMe version 3.3 driver.

Samsung Magician also shows that I've got the latest firmware and that the SSD does have a PCIe 3x4 interface.

I'm not running Magician because I've had a few quirks with it over the last couple of years.  I do have the latest firmware though.  I assume you're not having heat issues??

No heat issues.

And it has the latest firmware.

I'm having very similar problems with the latest top-of-the range XPS 8940.

• 11th Gen Intel® Core™ i9-11900K 
• Windows 10 Home 64bit
• NVIDIA® GeForce® RTX 3060 Ti™ 
• 16GB, 8Gx2, DDR4, 2933MHz
• 1TB M.2 PCIe NVMe Solid State Drive

Yesterday, I installed a Samsung 980 PRO PCIe 4.0 NVMe M.2 (Model: MZ-V8P2T0 in a SABRENT M.2 to PCIe X4 card (Model EC-PCIE) in the spare slot next to the graphics card.

I understand that the Dell XPS 8940 only supports PCIe 3.0, but it is one of the top 20 NVMe M.2 SSDs on the market, so there should be some noticeable difference in performance.

But it made no difference what-so-ever.  Both the SK hynix PC611 and the Samsung 980 PRO return near idential sequential benchmarks, whether run using PassMark, Crystal or now with Samsung Magician.  Magician reports sequential read speeds of 905 MB/s and 906 MB/s for the 980 PRO and the SK SSDs.

My conclusion is that something within the Dell configuration (motherboard, BIOS, drivers, etc.) is throttling both PCIe SSDs.  Otherwise there should be some difference in the benchmarks from two different SSD manufacturers and specifications.

mine is similar system:

xps8940   11700K processor, 

Nvidia 3070, 

Samsung NVME PM9A1, 64 GB memory, 

Win 10 pro, Killer WIFI

Further updates that may help others diagnose what is going on here:

After installation, various metrics and features of the Samsung 980 PRO were disabled in Samsung Magician, although the SSD was functional at the Windows 10 level.

Magician reported "Compatibility Issues" with the Intel Corp 18.31.2.1034 device driver.  I initially thought to test the bespoke Samsung device driver available with most Samsung SSD products to overcome this. But Samsung have not released a supported driver for the 980 PRO and expect to use the standard Windows drivers.  And Windows Device Manager showed that the Samsung Disk Drive was using a Microsoft driver.

Further investigation of the Device Manager folders traced the incompatible Intel driver to the Intel Rapid Storage Technology (RST) driver used to support RAID.

I changed the BIOS from RAID to AHCI - you need to restart Windows in Safe Mode to effect the change, or it won't boot up first time.

The Compatibility Issue went away in Samsung Magician.  I could now see that Device Manager under Storage Controllers showed the Standard NVM Express Controller was operational using Microsoft driver 10.0.19041.844.

Having read about the potential impact of RAID vs AHCI on SSD performance, I hoped the benchmarks would now improve.  But there was no difference for sequential read/write speeds!

However, the IOPS (random) rates improved for both the Samsung 980 PRO and the SK hynix drives by using AHCI.   I now get PassMark figures of 1286 / 1215 for the 32KQD20 test and 98 / 70 for the 4KQD1 test.  (Figures are for 980 PRO / PC611).

As expected, where the SSDs ability to push data across the Dell's PCIe 3.0 4x interface is not the limiting factor, the different SSDs' performance starts to become apparent.

A final test I've run using the PassMark Advanced Disk Test with both the Samsung and SK SSDs running sequential reads with very large block sizes, show both SSDs' transfer speed capped at almost exactly 500 MB/s each as they contend for PCIe bandwith.

It's as though the Dell XPS8940 is only using a single PCIe 3.0 bus lane running at maximum throughput - 1000 MB/s shared by the two SSDs at 500 MB/s each - instead of the 4x lanes (4 GB/s) it should be using.  

@1km1km1km I think you have hit the limitation of the DMI 3.0 interface between the PCH and the CPU. If you require high-performance graphics and high-performance SSD then the next step is a different CPU and chipset with more than 16.PCIe 3.0 CPU lanes. I think the work you did to analyze this problem was commendable. 

All - I contacted my Dell tech contacts about the SSD performance issue in the XPS 8940 ~1- 2 weeks ago.

I'll pass along the info that @1km1km1km posted which might help them figure out why the NVME slot is so slow..