SN850 1TB x2- very low IOPS reported (1/3 of expected) when benching

Hi all,

I have two SN850 1TBs. One is installed to a PCH M2 slot, one to CPU M2 slot.

Both are reporting IOPS at around a third of expected.

I have a 980 Pro on another PCH M2 slot and that’s reporting better. Through Samsung Magician, that’s reporting almost 950k Random Read, 916k Random Write. The SN850s using the same app, a third of that and consistently so.

980 Pro


Sequential Read and Write are as expected.

One SN850 has 785GB free, the other 90GB free, out of 1TB per.

Running on MSI MEG X570 Godlike on BIOS 1.D3 (not the latest BIOS, I know).

Any ideas?

Edit: Updated to BIOS 1.F4, no change.

Edit: Added screenshots of results.

Hi @SlowNVME850,

Please refer below link to help you with trouble shooting steps:

I am also, sn850,just a third of expected and installed to CPU M.2 slot too.
But when I asked the customer service, he said that the speed of read&write is correct, the product is no problem.I dont know why,wtf.

I know this thread is a few months old now but just to update on where things are…

  • No reply from WD Support for at least 2 months, since raising the ticket and supplying lots of info.
  • I’ve removed every PCIE device apart from the GPU - no difference
  • I’ve removed my secondary 850 from M2_3 leaving just M2_1 and M2_2 used - no difference

So in the above scenario, there is no impediment caused by additional PCIE devices throttling lanes and there is no impediment by having too many 850s on the onboard M2 slots, again potentially throttling.

This HAS to be an issue with the firmware and WD are being extremely tight lipped about dealing with it.

Did you find any solution to this problem?

Nope. No response from WD after all this time. I check periodically for new firmware, nothing.

I’ve given up but I have made the decision to never touch WD storage again. So their loss, when I come to my next rebuild, next year.

I did spend a bunch of time troubleshooting and only real gain was from disabling bitlocker. But it was marginal gain. Brand new notebook Dell Precision i9 processor, my last try will be W11 i know it head some problems at the beginning.

I would be really interested in how W11 differs, please do keep the post updated. It’s the one thing I haven’t tried yet, just because my system is used daily for work so I can’t afford the clone/reimage time ATM, should things go badly.

More research more results:

1st round of testing run on Precision 5470 - i9 - 12gen processor - PCI Gen 4 - 4 lines

  1. I did bought Samsung 980 PRO
  2. I did install W11/W10 with all latest updates on booth WD and Samsung
    Up to this point booth drives operate the same low IOPS at around 250k IOPS and about 5G Read performance.

Unfortunately WD don’t provide any drivers for NVME, but Samsung does.
After replacing (updating drivers for NVME for Samsung)
I was able to achieve 6.5G reading and small boost in IOPS 300K - 350K - so standard Windows drivers are… useless.

  1. Second round of testing run on Dell Latitude i7-10850H Gen 3 - 4 lines
    Tests run on WD only as i did clone my old drive
    Reading 3.5G and 840k IOPS
    I understand that Reading is limited by PCI but 840k IOPS looks nice on much older hardware

Latitude and Precision have different architecture and probably this is main problem.

Interesting but one point to note, I get the expected IOPS on my system with the Samsung 980 Pro. On the two SN850s, operating across CPU and Chipset lane based M2 slots, I get about 1/3 of the the expected IOPS and as the troubleshooting I went through shows, removing every other device operating on PCIE, apart from the GPU, got the same IOPS result, which pretty much assures this is a flaw with either the 850 drives, or the firmware is purposefully throttling IOPS performance for reasons we’re not aware of. OR, its a problem they simply don’t know how to fix.

Reads/Writes are fine, after the last big firmware WD did but IOPS were always crippled, throughout.

Interesting result, after cloning my old system from old Dell to Samsung performance was still far from perfect, but driver, update, windows update to KB5015807, and Dell Command update full success, Samsung is running at full speed.
Take a look at the list of last installed drivers maybe something will help for you.

Thanks for the update but Samsung has always operated at full read/write and IOPS. Its the SN 850 that has IOPS very low.