MP 7,1 GPUs in both slots 1 AND 2?

[DrEGPU]

I couldn't find the answer on google, so I'll ask here. I get a PCIe device error on startup when I put the RP580X MPX in slot 1 and a RTX 3090 in slot 2. Setting aside the folly of putting a 3090 into a 8x slot for the moment, why would this cause an error? Anyone else experience this? Does this mean slot 2 is unusable if an MPX is in slot 1? I'll do some more testing, but unplugging the all the cables before lifting this case is already getting old.

 

[DrEGPU]

UPDATE:

I put a AMD Radeon Pro WX5100 in slot 2 next to the MPX RP580X and still got a PCIe device error.

Putting a PCIe card with nvme storage, boots up fine.

I guess Apple doesn't want GPU's in both slot 1 AND slot 2 for some reason.

 

[h9826790]

UPDATE:

I put a AMD Radeon Pro WX5100 in slot 2 next to the MPX RP580X and still got a PCIe device error.

Putting a PCIe card with nvme storage, boots up fine.

I guess Apple doesn't want GPU's in both slot 1 AND slot 2 for some reason.

Did you connect the aux power cables correctly?

 

[DrEGPU]

Yes. The WX5100 has no pcie aux power connectors!

 

[TrevorR90]

When you say pcie device error are you referring to the amber lights on the power led?

If so, then no, I don't get the error, I've installed a 3090 in the 2nd slot and vega pro II in the first slot and no errors, boots right up.

 

[DrEGPU]

When you say pcie device error are you referring to the amber lights on the power led?

If so, then no, I don't get the error, I've installed a 3090 in the 2nd slot and vega pro II in the first slot and no errors, boots right up.

Yes, the amber power light flashing pattern indicates a PCIe device error.

I thought the Vega Pro II was a 4 slot card. How is it possible to put anything in slot 2?

 

[flowrider]

^^^^Yes, the Pro Vega II MPX covers slot two as does the Pro W5700 MPX. I don't understand Apple's wisdom for spending the design time and money including an 8X slot in the position. In normal use the slot is blocked. My Aorus RX5700XT also covers the slot. My Pro580X is mounted in slot three.

It can only be used in conjunction with a skinny card like the 580X, the 5500X and your WX5100.

Lou

​

 

[DrEGPU]

Oops! Finally this on Apple’s site. They don’t really explain why this doesn’t work, but they do explicitly say it will not work. I guess slot 2 is disabled in windows? Doesn’t explain why it won’t even boot though.

 

[DrEGPU]

I mean this:

 

[joevt]

So what's special about slot 2? The document at https://www.apple.com/mac-pro/pdf/Mac_Pro_White_Paper_Feb_2020.pdf says "When an MPX Module is installed in bay 1 (slots 1 and 2), slot 2 is disabled and its PCIe lanes are routed to the MPX connector in bay 1. When an MPX Module is installed in bay 2 (slots 3 and 4), slot 4 is disabled and its PCI lanes are routed to the MPX connector in bay 2." I think the info for bay 1 is incorrect, because later it says about the Radeon Pro 580X "When a half-height MPX Module is installed, an additional double-wide PCIe slot (slot 2) is available." You said you could put a PCIe card with nvme storage in slot 2 with the Radeon Pro 580X in slot 1 without error. Does that mean the NVMe works? That would confirm the info about the Radeon Pro 580X in that document.

Does slot 4 allow x8 when a half-height MPX Module is installed in Slot 3? There's a picture on page 11 that shows x8 for slot 4 when a full-sized MPX module is installed. But that same picture shows x0 for slot 2 when a full-sized MPX module is installed in slot 1. As far as I know, the MPX slot only requires x8 for the two Thunderbolt controllers of an MPX module - the rest of the pins are for four DisplayPort connections and USB and some other stuff.

Is there a problem with other slots such as slot 4? Slot 3 has a direction connection to the CPU like slot 1 so that's the next best slot to use.

 

[DrEGPU]

Yes the nvme drive in slot 2 (with the RP580X in slot 1) works just fine. Mounts, reads, writes, etc.

I’m a little less sure about the direct connection of slot 2 to the CPU. I think it is just disabled if there’s a 4-slot mpx module. The rear mpx connectors look like an 8x slot.

I’m still confused about the Mac Pro allowing storage but not GPU functionality in that slot.

But yes, I went back to putting my 3090’s in slots 1&3 with a single slot WX5100 in slot 7 (nvme storage in remaining slots).

If I could opine for a second, it would’ve been really nice if Apple had used AMD TR or Epyc and enabled PCIe. 4.0. This would have allowed me to load all my NVME storage onto a single card (i.e. one with 8x NVME connectors), freeing up more slots as well as giving the 3090s full bandwidth. Same for people that are using the Radeon Pro VII!

 

[joevt]

Slot 2 is not directly connected to the CPU. It is connected to the 96 lane switch like all the other slots (except slot 1 and 3) and the Thunderbolt controllers.

I'm 60% sure that it might be possible to use slot 2 when there's a 4 slot MPX in slot 1 by using some kind of low profile riser but I don't know how much clearance there is between slot 2 and the underside of the MPX. The cable at http://www.adt.link/product/R11SL.html requires 6mm of clearance but maybe you can shave off a couple millimeters if necessary.

Have you tried the RP580X in Slot 3 to see if Slot 4 runs at x8?

 

[DrEGPU]

Have you tried the RP580X in Slot 3 to see if Slot 4 runs at x8?

I'm tired of swapping cards around so many times. I fear I might be the first person to actually wear out the case! I might try your suggestions after getting some actual work done, though.

 

[DrEGPU]

I'm 60% sure that it might be possible to use slot 2 when there's a 4 slot MPX in slot 1 by using some kind of low profile riser but I don't know how much clearance there is between slot 2 and the underside of the MPX. The cable at http://www.adt.link/product/R11SL.html requires 6mm of clearance but maybe you can shave off a couple millimeters if necessary.

Maybe, but I doubt it. The coolers on these GPU's have very, VERY low clearance. I guess I could try bending the heatsink fins a bit, but I don't really want to do that.