Question Need some help with pcie lanes and bifurcation.

[d__]

Hey all, this is my current build:
https://uk.pcpartpicker.com/user/Way2Close/saved/HxnVBm

I foolishly asked google gemini if pcie slot 4(x16) supported bifurcation and it said yes so i bought:

ASUS HYPER M.2 X16 CARD V2 GEN4
https://www.amazon.co.uk/gp/product/B0863KK2BP/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Then I found out only slot 1(x16) and slot 2(x16) support bifurcation, so the question is, given that the 5950x supports 24 lanes, how much of a hit would my gpu take if i populate slot 2 with 4x4x4x4x bifurcation?
[it is fully populated with 4 nvme drives, also none of the drives are for game storage, that is on my main nvme nearest the cpu on the mobo]

Thanks guys

 

[Math Geek]

looking over the spec sheet, manual and pics of the mobo, it appears that the top 2 slots are from the cpu. if using both then they both drop to x8 lanes.

your gpu would take a slight hit due to only being 8 lanes (which makes it pcie 3.0 x16). though it should not really be noticeable unless you focus on nothing but benchmark numbers. all the testing i have seen show barely any drop at all.

the bigger "issue" is the add-on card. it is also in a slot that is now pcie 4 x8. each ssd will still have 3.0 x4 lanes worth of bandwidth, but if you bought pcie 4 ssd's then they are only at half bandwidth. depending on what you bought it might not be an issue at all. but if you went high end, then you ended up wasting your money overall.

using the 3rd slot for the add-on card would leave the gpu in slot 1 as x16 and the 3rd slot is also x16. i do not see any info about bifurcation of any of the slots, so not sure where you saw/found this piece of info. have you tried the card in the 3rd slot to see if it works?

 

[d__]

looking over the spec sheet, manual and pics of the mobo, it appears that the top 2 slots are from the cpu. if using both then they both drop to x8 lanes.

your gpu would take a slight hit due to only being 8 lanes (which makes it pcie 3.0 x16). though it should not really be noticeable unless you focus on nothing but benchmark numbers. all the testing i have seen show barely any drop at all.

the bigger "issue" is the add-on card. it is also in a slot that is now pcie 4 x8. each ssd will still have 3.0 x4 lanes worth of bandwidth, but if you bought pcie 4 ssd's then they are only at half bandwidth. depending on what you bought it might not be an issue at all. but if you went high end, then you ended up wasting your money overall.

using the 3rd slot for the add-on card would leave the gpu in slot 1 as x16 and the 3rd slot is also x16. i do not see any info about bifurcation of any of the slots, so not sure where you saw/found this piece of info. have you tried the card in the 3rd slot to see if it works?

It's currently in the 3rd slot and only one nvme shows up, which is expected without bifurcation. I found out about the bifurcation when i tried to enable it in bios and there is no option for it, only slot 1 and 2. I don't suppose you know if there is a work around to be able to use slot 3? Thanks for your help though, much appreciated friend.

 

[Math Geek]

i have never really looked into how this is implemented. so no idea if it is a hardware limitation or something a bios update/hack could enable. some light searching and probably some reading could help shed some light on it.

so sadly i can't be of any help there. looks like for now, the best you can do is the 2nd slot and deal with the half bandwidth for each drive. real world testing i have seen shows little to no perceptible difference between pcie 3 and 4 for ssd's anyway.

sure specific benchmarking tests can show it, but real world what i have seen makes almost no difference except in those specific workloads the bench marks test.

wish i could offer more, but not well versed in that area yet.

 

[d__]

i have never really looked into how this is implemented. so no idea if it is a hardware limitation or something a bios update/hack could enable. some light searching and probably some reading could help shed some light on it.

so sadly i can't be of any help there. looks like for now, the best you can do is the 2nd slot and deal with the half bandwidth for each drive. real world testing i have seen shows little to no perceptible difference between pcie 3 and 4 for ssd's anyway.

sure specific benchmarking tests can show it, but real world what i have seen makes almost no difference except in those specific workloads the bench marks test.

wish i could offer more, but not well versed in that area yet.

Thank you very much for your help, take care.

 

[Math Geek]

no prob, i put the word out to see if anyone else might know something here. so stay tuned for possible other input