Question NVMe drives suddenly underperforming


May 30, 2020
Hi everyone,

I have my MSI MEG X570S ACE MAX mobo for about 3 weeks now. Right after installing the mobo I benched both my NMVe's and the results looked alirght. The drives are Samsung 980 Pro 1TB (installed into M.2_1 [CPU]) and WD Black SN850 2TB (installed into M.2_4[Chipset]).
The only change since then was that I set the PCIE_1 slot to Gen 3 because I use a ROG Strix GPU riser. Yesterday I noticed that the 980 Pro was heavily underperforming, especially on random I/O. My first thought was that is was somehow related to the PCIE_1 running in Gen 3 mode, so I moved the drive into M2_2 (Chipset) with interesting results... this inreased sequential read by 50%, random read by around 10%, but random write actually dropped by almost 100%. Here are the results from Samsung Magician, from top to bottom:

  1. Using M.2_2 slot
  2. Using M.2_1 slot (probably) after changing PCIE_1 to Gen 3
  3. the initial bench after just installing the mobo, M.2_1 slot

Afterwards I benched the WD SN850 - interestingly, compared to the original bench, it has "only" lost a lot on random I/O, but not sequential:

At this point I have absolutely no clue about what's going on... I also don't have any SATA devices connected. Since the mobo is still quite a new product, can a firmware bug cause the behavior? Any input appreciated.

EDIT wasted a lot of time removing the riser and setting all PCIe slots to Gen 4, no difference whatsoever... there were some Windows updates since the last "OK" bench, guess will have to try to uninstall them and recheck
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