Question Can't run dual GPUs on a Maximus X Formula?

[M1nat0]

I thought my Titan XP was dying, so I bought another used one bc it's what I could get. I've since found out mine is fine and so decided to run SLI.
However, my Maximus X Formula (9900K, BIOS 2701) will not [] detect both cards simultaneously. Both work fine on each of the two slots on their own, but no matter which one I put on top, they won't work in tandem, won't appear in NV Control Panel and won't appear both in BIOS. When I connect the EVGA GHB SLI bridge thst I have, the top one is detected in x8 speed. When I take it out, the bottom one is detected, but never both.

How would I go about troubleshooting/fixing this?

 

[Karadjgne]

One of the downfalls of sli, they always run at x8/x8 so the board is seeing 2 cards populated if nothing else is.

 

[M1nat0]

One of the downfalls of sli, they always run at x8/x8 so the board is seeing 2 cards populated if nothing else is.

Yeah I'm not expecting them to run x16/x8. What I'm saying is no matter what I do, the MB only detects one at a time, although which one varies, and always at x8 speed, even if it's the top one and it only detects that one.

 

[M1nat0]

Have you tried removing one of the m2 drives to see if that makes any difference. Only so many lanes on z370 and with 2 x m2 and 2 x gfx it may not like it.

You would expect it to default to a lower speed to compensate but worth ruling out

I thought about it but I was dreading it as getting to them is a pain, but I'll try later and update this answer with the results.

Update: taking out the M.2 drive in the M.2_2 slot (which was running in x2 mode) did nothing. Taking out the M.2 one in the M
2_1 slot (which was in auto mode) also did nothing.
I have 2 more SATA SSDs, 2 SATA HDDs and 1 BD R/W drive. I don't think that's enough to bungle this up though, right?

 

[DRagor]

All drives on this board use chipset lanes, while both x16 slots use CPU lanes, so they don't interfere with each other. I have to agree with Karadjgne that board sees both slots populated, otherwise it would run the top one at x16. That means the board is fine, it should work, just we are missing something. The BIOS on this board should have info about connected GPUs I think? Did you checked what it says?

 

[KyaraM]

Hmmm, according to the German specs it is supposed to have 2-way SLI 3-way Crossfire, so technically should work.

I read somewhere that newer drivers might not allow for SLI anymore of cards that aren't a 3090. I don't know if that is true, but just in case, what driver version are you using? Did you try an older driver already?

 

[Karadjgne]

The cpu has 16 pcie lanes dedicated to the top 2 gpu slots. When both cards are present, it changes from x16/x0/x4 to x8/x8/x4. Both lanes use the same bandwidth section of cpu lanes.

In 40+ years I've never heard of a cpu burning out pcie lanes because it was overclocked. That's a whole different area of the die, not related to the cores. I have heard of incorrect mounting pressure causing pcie lane errors, ram errors, but never burn out.

Might want to check the vbios of that new card in depth. It's possible it's not really a Titan XP, could even be a mining card with fake vbios or Titan X etc which would prevent SLI. Just having the right shroud physically doesn't make it the right card underneath. I say in depth, even to verifying the actual die physically because it's not that hard to change the identifiers to say XP but there are physical things that cannot be changed.

The basic WHQL drivers are all the same, for all nvidia cards, they are also included in all Windows versions and get updated with Windows updates. It's the advanced files that are custom to each chipset, especially pertaining to game settings/bug fixes. So any new driver files will include SLI requirements on a chipset by chipset basis. Nvidia hasn't stopped support for SLI as such, just really hasn't developed the tech any further than where it already is, because newer games aren't including SLI ability in their coding.

 

[M1nat0]

Hi all!
I enabled Above 4G Decoding because I read somewhere it helped for 2+ GPUs, and it also turns out that when I originally installed the 2nd one I might've not inserted one of the two PCIe cables fully and it wasn't completely in.
One of those two fixed it, and it now works!

I learned a lot and got a lot of help even though it was my first time on a forum like this. Thank you sincerely to everyone who helped!