Hello,
I recently completed a build that doesn't (completely) work, I believe the issue is that I have too few PCIE lanes. The purpose of this post is twofold:
1. I want to understand how PCIE lanes work, specifically what is the interaction between lanes on the chipset and lanes on the CPU, and when is each relevant
2. How can I run this 4X m.2 NVME expansion card: https://www.asus.com/ca-en/Motherboard-Accessories/HYPER-M-2-X16-CARD-V2/
What I originally purchased is this motherboard: https://www.aorus.com/X570-I-AORUS-PRO-WIFI-rev-10
And this CPU (Ryzen 3400G): https://www.amd.com/en/products/apu/amd-ryzen-5-3400g - picked it specifically for the integrated graphics as the motherboard only allows one expansion card and that is held by the Hyper M.2 card, so no discreet GPU possible with that motherboard.
Additionally, I have a 5th NVME drive that attaches to the motherboard.
PCIE Lanes
The CPU has 20 lanes, 4x used to connect to the motherboard, leaving 16.
But it turns out the integrated graphics in the Ryzen 3400G uses 8x PCIE lanes from the CPU
(source: [MEDIA=reddit]Amd/comments/7usqkn[/MEDIA])
leaving only 8. And I need a full spare 16x for the Asus Hyper card.
What about the 5th NVME drive on the motherboard? Does it subtract from CPU PCIE lanes? Or does it use lanes on the motherboard and not impact the CPU? I am pretty confused about the interaction of lanes on the CPU and motherboard.
Saving the build
So my next thought was, if I upgrade the chipset from Mini-ITX to Micro-ATX, I'll get an additional PCIE slot, and I could run a discreet GPU with a Ryzen 3700X (no igpu), to free up the 8X lanes that the integrated graphics was taking. Or would that just shift the lane consumption problem from integrated graphics to discreet?
I found this thread where someone has a working microATX setupt that sounds like what I want, but missing some key details: https://linustechtips.com/main/topic/1040947-pcie-bifurcation-4x4x4x4-from-an-x16-slot/?tab=comments#comment-13113500
- here is the mobo he is using: http://asrock.pc.cdn.bitgravity.com/Manual/X570M Pro4.pdf
But I'm wondering how he overcame the PCIE lanes issue? Is it possible he is running a discreet GPU, as well as the Asus Hyper card with all 16x lanes? Or must he be swapping discreet GPU out after initial configuration, to use the Asus Hyper card?
As a last-ditch effort, I'm considering giving up on Ryzen and going to Threadripper as it has 60 Lanes and all these problems would go away -- however it has a much larger TDP which I was hoping to avoid.
