[SOLVED] Problem when trying to connect 5 gpu

[Jonyon]

Hello,
I have a brand new supermicro c9z390-pgw motherboard, and 4 brand new geforce gtx 2080 ti and also geforce gtx 1080 ti and i want to connect them.all to.my motherboard.
When i connect all 4 gtx 2080 to the pci x16 everything work great but ONLY if inset in the BIOS allow 4g decoding to DISABLE ! if it enable it stay stuck on the bios screen and not boot.
I tried to connect also the gtx 1080 with a riser connector to the pci x1 slot but then it boot automatically (very slow) directly to the bios and i get message pci out of resources condition , I then tried to enable above 4g decoding and it wont boot and stuck at the bios logo screen, when I disconnected the gtx 1080 and again disabled the above 4g decoding its boot gteat.
Can you please help me?

Best regards

Jon

PS
My psu is 1800 w and I've also tried to connect the gtx 1080 to other psu so its not a power issue
The bios version is 1.1 and it is the latest BIOS version as mentioned in supermicro's website.
Please help me

Thanks

 

[sizzling]

I am unsure but my first thought is the Z390 platform doesn’t have sufficient pcie lanes for such a setup. Might be something to try looking into.

 

[Jonyon]

Even with the 4x16 pci Express and the 1x1 pci slot?
And what do you think about the 4g decoding that its working only if it disabled? Isnt it weird?

 

[sizzling]

Ok I am guessing but gpu’s normally use 8 or 16 pcie lanes but can operate with 4. The best CPU’s on the Z390 platform only have 16 pcie lanes. For example the 9900k can support the following “Up to 1x16, 2x8, 1x8+2x4” taken from https://ark.intel.com/content/www/u...9900k-processor-16m-cache-up-to-5-00-ghz.html

It seems to specifically leave out 4x4 as an option.

 

[Jonyon]

This is exactly the cpu I have,
So you mean that I cant connect more then 4 GPUs?
And if I will change the motherboard to one that can support more then 4 GPUs? Or is that the problem is the mother and the cpu and even if I will replace to different motherboard I will have the same problem because of the cpu?

 

[sizzling]

This is exactly the cpu I have,
So you mean that I cant connect more then 4 GPUs?
And if I will change the motherboard to one that can support more then 4 GPUs? Or is that the problem is the mother and the cpu and even if I will replace to different motherboard I will have the same problem because of the cpu?

I’m not an expert but based my limited knowledge of how pcie lanes work I don’t think you can. I believe you need an Intel X299 or AMD TR4/TRX4 platform. Hopefully someone better informed can jump in.