Over utilization of PCIE lanes

Skippy102595 · August 8, 2023

Hello everyone,

I added a bunch of upgrades to my gaming PC this weekend & I have been working on fine tuning everything when I ran into a big problem today.

After this weekends upgrades my specs are:

Gigabyte Aorus X570 Elite WiFi
Ryzen 9 3900x
Corsair H100i RGB AIO
6x 120mm case fans
32gb (4x8gb) Corsair Vengeance LPX DDR4 3200
Gigabyte RTX 4070 12gb (into 16x PCIe)
Gigabyte RTX 2070 Super 8gb (into 4x PCIe
Corsair RMx850 shift series
500gb NVME m.2 boot drive
1TB NVME m.2 storage drive

The whole point of these upgrades was to give my PC a refresh and enable me to have more output connections for the stupid amount of monitors I have. Anyways, after shoving all this into the case, the system posted and I was able to format my new 1TB m.2 & get both my graphics cards to run a game independently of one another.

However, I realized the XMP for my ram was not working properly and kept causing crashes and after doing some research i decided a BIO’s update was in order as my BIOs system was 3 years out of date. Upon successfully updating the BIO’s the system would not post. I panicked, Q-flashed it back to where it was and it still didn’t post. So I started yanking out graphics cards and eventually discovered that the system would post if I only had 1 graphics card in (despite it working yesterday without issue).

After calming down and realizing that I didn’t just brick my PC, I did some more research and learned that apparently having both M.2 slots & both PCIe slots in use is not possible in most situations due to the limitations of available PCIe lanes.

Does anybody know if that information is true and if not how would I go about making it work? In the end, I just removed the newest m.2 drive I had added and the PC posted, but I would like to find a solution that would enable me keep the system as it was before I updated the BIO’s (which did fix my XMP problem). My Motherboard does allow for bifurcation but it seems to only effect the PCIe 16x slot.

Any advice is appreciated, Thanks!

Kilrah · August 8, 2023

From the mobo manual there doesn't seem to be any slot exclusions/sharing so using both m.2 and the PCIe x4 slot should be possible.

PDifolco · August 8, 2023

I have a similar build iirc you can use the CPU x16 lanes and split them x8x8 to slot 2 GPUs, then you'll use the chipset lanes only for M2 and stuff like wifi card

In my rig I only have 1 GPU, tested it works in both CPU lanes, and have a Pcie M2 adapter and a Wifi card in the chipset slots, no issue

Skippy102595 · August 9, 2023

16 hours ago, Kilrah said:

From the mobo manual there doesn't seem to be any slot exclusions/sharing so using both m.2 and the PCIe x4 slot should be possible.

Do you think I am on the right track with this issue though? If pulling one of the 2 GPU’s out or the m.2 allows the system to post is the issue with PCIe lanes?

Skippy102595 · August 9, 2023

Tied messing with this more last night and had no luck. I tried playing around with Bifurcation settings but none of them enabled me to get the PC to post with the 2nd m.2 slot in use.

if I understand this correctly, my 2 graphics card are taking up 20 of the 24 available lanes? The other 4 pass through the chipset and I’m not sure how to use them.