Question Using RTX 4090 with a PCI E Gen 4 x16 NVME extension could cause issues?

[tygzy]

I'm thinking of buying the Asus ROG Strix B550 XE motherboard that comes with the NVME extension card as an upgrade to my old motherboard so I am able to use 2 Gen 4 PCI E slots for my graphics card and an extension card to use 4 more NVME's with it. But going through youtube reviews of the motherboard someone said that there could be issues with the NVME extension card and a higher end graphics card if they are used at the same time because of how the lane structure works and would half the amount of lanes available for the GPU. The reason I've come here to ask is because the video was made a long while ago and the reviewer wasn't sure as they hadn't tested it yet so since it's been out for quite a while does anyone know if it would create an issue.

To note though I'm not sure if it's relevant, I will be using both of the build in motherboard nvme drives in addition to the PCI E NVME extension card

Relevant specs:
AMD 5800x
Asus ROG Strix B550 XE
RTX 4090
Asus Hyper M.2 x16 Gen 4 Card

 

[Eximo]

Yeah, that won't work like you plan.

You need at least 8x to run an Nvidia GPU under normal circumstances, but ideally it would get all 16 lanes. Your other x16 slot is shared with that slot.

Each M.2 drive needs 4x lanes for full speed, so you can't have all 4 drives and the GPU at the same time. You would need 32 lanes. And the 5800X only offers 20 lanes, plus the chipset.

You could do two drives and still run the 4090 at 8x.

 

[tygzy]

Yeah, that won't work like you plan.

You need at least 8x to run an Nvidia GPU under normal circumstances, but ideally it would get all 16 lanes. Your other x16 slot is shared with that slot.

Each M.2 drive needs 4x lanes for full speed, so you can't have all 4 drives and the GPU at the same time. You would need 32 lanes. And the 5800X only offers 20 lanes, plus the chipset.

You could do two drives and still run the 4090 at 8x.

Okay thanks, is that last comment about two drives meaning 2 nvme drives in total, or 4 including the ones on the motherboard and then 2 additional drives on the pci e card?

 

[Eximo]

That should work. You'll have one M.2 connected to the CPU connected M.2, one M.2 connected via the chipset (only PCIe 3.0 though, and it would share total bandwidth with everything else connected to the chipset back to the CPU)
And then the second x16 slot is likely only wired for 8x, split into to two 4x connections, and leaving 8x for the GPU (Any use of that second x16 slot will drop the primary to 8x.

Just becomes a question of how your PCIe to M.2 adapter behaves and if your motherboard will split the 8x connection.

I though the Hyper M.2 cards generally came with specific motherboards, but I am not 100% certain.