I HATE the lack of pcie lanes on consumer motherboards, but I’ve found two motherboards that support dual pcie 5 (x8) which would allow for dual gpu, mainly for VFIO pass through, but possibly also some more intense AI workloads (if I were to go with a second nvidia gpu)
The reason I am doing this upgrade (after only a couple of months of owning my current rig) was realising that I only had 1 pcie4x16 slot and 1 pcie3x1 slot on my b650 motherboard, I had acquired an optane drive that needs pcie3x4 and checked my motherboard specs and realised any of my Vfio and optane plans were ruined.
The great thing about the (way to expensive) asus motherboard (the asus pro art x870e) is that it has two pcie5x16 slots that lane share (x8x8) for minimal performance loss in a dual gpu setup. It also has a pcie4x4 slot which is exactly what I need for my optane 900p pcie drive. The only other motherboard that i have found that has similar pcie connectivity is the MSI X870E Godlike which is more than double the cost of the Asus pro art.
I was wondering if anyone else has attempted something similar on consumer class hardware, if they have found any other good motherboards for AM5 in that case, and if I should just save up and do a server build with old xeon cpus instead, where I have access to more PCIE (although with more outdated hardware)
Note that on the Asus ProArt X870E, if you populate the secondary PCIe Gen 5.0 M.2 slot (M.2_2), the secondary PCIe Gen 5.0 x16 slot (PCIEX16(G5)_2), will be dropped to x4 mode. I’m guessing this is not a deal breaker for you since it’s Optane storage that you’re trying to go for, but just be advised that if you also plan to run two Gen 5.0 M.2 drives at some point, the best your GPUs will be able to do is 8x/4x. This might be totally fine depending on what you’re trying to do with your secondary GPU.
At least the ProArt provides a way to get 8x/8x bifurcation for dual-GPU set-ups. Many (most?) of the AM5 mobos I’ve seen only offer 8x/4x.
The user manual suggests that this may be exactly what you do not need. The PCIe 4.0 lanes are chipset lanes, which will neutralize a chunk of the Optane latency advantage over regular NAND SSDs.
Get a M.2-to-U.2 adapter and attach your Optane that way to CPU-connected PCIe lanes. Or:
I am going to test out a setup with a PCIe 5.0 switch to break out 8 PCIe 5.0 lanes into 32 PCIe 3.0/4.0 lanes. (I just got it.) It could be another solution, but much more expensive, and at that point you should probably be going for a workstation or server-class solution for native high-count PCIe lanes.
Yes th x8 x8 was my plan, from benchmarks it seems like on gpus x8 only has a 3 percent or so performance delta from the full x16, and given that I want to do vfio, ai, etc the slight decrease in fps in games is something I’m very much ok with, I will simply not use the m.2 slot with the shared gpu lanes. The one thing that concerns me now is whether the chipset based pcie4x4 slot will significantly bottleneck the optane drive. I recently benchmarked the optane 900p in a pcie3x1 chipset slot and it was significantly hampered but my guess is that is mostly down to the slot itself. (I also somehow managed to brick my partition table for my linux installation playing around with it, not sure exactly what happened) but I guess since im rebuilding the computer anyway its not much of an issue, I did want to change some stuff around anyway
using a m2 to u.2 adapter or more precisely an m.2 to pcie adapter is something i am considering but due to the fact that I only have two m.2 slots that go directly to the cpu, and one bifurcates the second pcie5.0 slot to x4 there isnt much reason to currently. what I am considering doing is putting the optane in the second pcie5 slot for an x8x8 with my gpu as I dont currently have a second gpu to occupy that slot with.