Secondary NVMe drives in M.2 slots running off PCH - 50% write speed @ PCI 4.0 4x

[Solace]

Anyone else have dual 4.0 nvme drives and notice the second has balls performance? I recall seeing normal speeds in the primairy nvme slot however the one running off the SB chipset seems to be hindered quite a bit and quite noticable on writes by 50% despite there is no card populating the PCIe slot that shares the PCIe lanes... The drives run both @ PCI 4.0 x4 and are NOT splitting lanes

x570 msi carbon wifi pro is the board on latest firmware

 

[Solace]

The bottom one is obviously on the PCH, read speeds seem fine and weirdly enough random4k has higher write than the other... although the firmware do differ and ill correct that later. The firmware is not responsible for the massive drop though as the second photo was in the other drive slot until recently and benching fine earlier.

Closest information found,

WD SN850 Slower than expected performance

Don't compare to reviewers using it as 2nd non-OS drive especially not if its emphy, numbers will always be better, it looks fine to me, i have 970 Evo, 970 Evo Plus, SN750 and SN850 + 980 Pro and the SN850 is the fastest of them all altho 980 Pro is close and wins some tests but overall SN850...

www.techpowerup.com

Something to do with 128byte PCIe bus... Wonder if other MFG are lazy/behind patching unless people start kicking and screaming.

Edit: the MFG manual shows the WIFI running off the PCH, disabling that appears to be the workaround, whining to adata I suppose is the long term solution if another drive fails to solve the problem since others claim WD released a firmware to negotiate better on 128bit bus. I hit roughly -10% of expected speeds even with disabling but at least the write hit 6000+

 

[Sagath]

Yep. It could be a lot of things stealing lanes. Onboard sound and USB slots in use and/or wifi among whatever else the manufacturer piggybacks on the chipset.

Realistically I doubt you'll be able to maintain 100% performance of that drive in the #2 slot.

Curious though. Is this more out of concern you thought you had a problem with the drive, or do you need the performance?

 

[Bond007]

Not surprised at all. It seems like almost every motherboard's 2nd (or more) m.2 (nvme) slot have reduced lanes/ shared lanes/ feed from add on chip/ etc...all of which will give reduced performance (extent will vary wildly from one board to another and potentially based on what other ports/slots you are using). I usually recommend the faster OS/primary nvme in the main slot, and to save some cash on a mid level nvme for any other slots (if it is required).

 

[Shadowarez]

I'll post some of mine from the Asus Dark Hero shortly as I don't use the onboard sound or wifi or Bluetooth for that matter and no spinning rust.

 

[sswilson]

Is there a decent written review on the motherboard that goes into the layout of the lanes as well as it's "shedding" profile when hardware starts to max out lane use?

I know my MSI B550 board has very specific restrictions on the second NVMe slot once you start to use the secondary PCIe slots. Most boards start shedding Sata ports, but my MSI was an outlier in that it downgraded the second slot's capabilities.

I know you said you didn't have anything populating the second slot, but maybe there's something else going on WRT lanes being used?

 

[Sagath]

Is there a decent written review on the motherboard that goes into the layout of the lanes as well as it's "shedding" profile when hardware starts to max out lane use?

I know my MSI B550 board has very specific restrictions on the second NVMe slot once you start to use the secondary PCIe slots. Most boards start shedding Sata ports, but my MSI was an outlier in that it downgraded the second slot's capabilities.

I know you said you didn't have anything populating the second slot, but maybe there's something else going on WRT lanes being used?

Its just a designer layout choice, not really particular to the motherboard. Just "X570 things"

The CPU direct link has -
16x GPU & 8 PCIE lanes to divvy up.

After that ANYTHING through the chipset is limited to the chipset to CPU buss of 4x. They all share it. USB, Sata, Wifi, nvme. Doesnt matter.

 

[Shadowarez]

had me curious seems as ssd is giving me some worrying numbers. yet in the abrent software its giving me proper numbers.

 

[moocow]

Anyone else have dual 4.0 nvme drives and notice the second has balls performance?

I suspected the 2nd slot would get slower performance regardless of generation because it's shared with other stuff. That's why I only use a SN550 for Steam on the 2nd slot while I left the SN570 for OS in the first slot. On my X470 board, it disabled the last PCI-E slot as well since it's NVME. I believe if you stick a SATA M2 the slot would work, but still, no reason to go back to SATA these days.

 

[Solace]

Yep. It could be a lot of things stealing lanes. Onboard sound and USB slots in use and/or wifi among whatever else the manufacturer piggybacks on the chipset.

Realistically I doubt you'll be able to maintain 100% performance of that drive in the #2 slot.

Curious though. Is this more out of concern you thought you had a problem with the drive, or do you need the performance?

I get 90/100% with the onboard Wifi disabled, ironically Sata ports run off the PCH too and disabling 4 SSD's did nothing as well lol... It was only the WIFI being disabled that ever mattered. Its more or less I paid for the performance and should be seeing it else I would just buy a PCIe 3.0 device at half the cost.