Adding a 2nd Nvidia GPU - any head's up?

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Adding a 2nd Nvidia GPU - any head's up?

Postby KA1J » Sun May 17, 2020 6:43 am

I want to put a GTX 1080 and a RTX 2080Ti in the same computer, I don't care which is used for video, it'll be connected to the monitor with HDMI, both cards are here only for folding, I have no games installed.

Is there an advantage to using the slot closest to the processor with either one of these cards? Is there anything I should do to get the most out of these both running in the same computer?

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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby PantherX » Sun May 17, 2020 8:03 am

Assuming that the motherboard has PCIe lanes which are Gen 3.0 and with both slots populated, they will run at 8x, then from what I have read, there shouldn't be any performance impact.

Since both are Nvidia GPUs, you will need to ensure that you have 2 spare CPUs free to feed the GPU. Also, I would connect the monitor to GTX 1080 as rendering the video/screen will have a slight performance impact which means lower PPD so would leave the RTX 2080 Ti for maximum folding performance and take the slight hit on the "slower" GPU. Also, ensure that you have sufficient cooling and power for the system.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby KA1J » Sun May 17, 2020 8:41 am

I have a new EVGA 850 Gold PSU, there are plenty of the 8 pin power plugs for both boards Both of these blow the air out the back & the basement's the coldest room in the house what with heat rising in winter & the AC flowing downstairs all the time.

Does it matter if the 2080Ti is in the nearer slot to the processor?

Sounds like it'll be OK :D
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby foldy » Sun May 17, 2020 8:51 am

It depends on your motherboard. If it splits the pcie slots speed equal from 16x to 8x + 8x then it doesnt matter. But if it splits it to 16x + 4x then the fast GPU needs to go into 16x speed slot and the slow GPU needs to go into 4x speed slot. Sometimes it also depends on CPU pcie lanes capability. What is you motherboard type and CPU? Typically the slot next to the CPU is the fastest pcie speed slot so your RTX 2080ti goes to the slot next to the processor.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby Neil-B » Sun May 17, 2020 9:38 am

In sig block of op
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2: Xeon E3-1505Mv5@2.80GHz, 32GB DDR4, NVME, Win10 Pro, Quadro M1000M 2GB, FAH 7.6.13
3: i7-960@3.20GHz, 12GB DDR3, SSD, Win10 Pro, GTX 750Ti 2GB, FAH 7.6.13
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby foldy » Sun May 17, 2020 10:40 am

A sig block says ROG Strix Z390-E so it has 2 pcie slots running at x8 with dual GPU plus a 3rd pcie slot running at x4. So you want to put both GPUs in the 2 upper pcie slots next to processor. It doesnt matter which one goes most upper. https://www.asus.com/Motherboards/ROG-S ... fications/
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby Frontiers » Sun May 17, 2020 4:16 pm

Top slot is little bit faster in x8 + x8 mode, because it will have direct 8 PCIe lanes from CPU without routing them through Asmedia PCIe switches.
But bottom slot (from 2 slots connected to CPU) is colder, especially for 2080 ti, because with aircooling bottom slot is is always colder even with blower cooled cards.
Personally me wouldn't install in same machine assembled in regular case 350+200 watts of GPUs without watercooling.
So if you don't have watercooling - single 2080 Ti is safer decision in the long run, and it is already Folding Monster with 3x PPD of 1080.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby MeeLee » Sun May 17, 2020 4:56 pm

If you're planning on putting the fastest GPU in the first slot, I would use a ribbon riser and mount the GPU a bit away from the motherboard.
One issue with RTX GPUs of 170W and up, is that they will blow their hot air out on both the top and bottom.
Not an issue at lower watts, but once it gets to 225W you could potentially get into a thermal throttling situation, where the GPU will run hotter than usual, due to it sucking in hotter air, which makes it run even hotter, exhausting even hotter air, ... and so on...

What happens is that some of the air from the bottom air vents, bounce off the motherboard, and flow right back into the fans, making open coolers only 66% efficient.
Some of the other air may be blocked by m.2 heat shields, or other electronics mounted under the GPU, causing the cooling solution not to efficiently get rid of the heat, trapping some parts of the cooling solution.
Adding a second GPU in the bottom slot, will lower that efficiency even further to 50%, as most of the air exited on the bottom will be returned back into the cooling fins.

For that reason, if you're running 2 GPUs, and your motherboard supports a x8/x8 slot configuration (both the same, preferably PCIE 3.0), it is best to actually put your fastest GPU on the bottom, where it gets better cooling, rather than on the top, where it gets 'faster' PCIE support.

The difference between x8 main slot, and x8 second (or third) slot, is very minimal; not noticeable.

If however, you can somehow mount your GPU in a different location, where it gets better cooling, and using a PCIE x16 ribbon cable, the first PCIE x16 slot is the best option for your fastest GPU.

I myself mount my primary GPU over the CPU, where the backplate gets actively cooled by the CPU fan sucking away the heat, straight in the CPU cooler. The CPU runs hotter, but with it getting 75-80C is still within tolerances.
(Intel) CPU's of 7/8/9th and 10th gen, can handle hot temperatures a lot better than GPUs, and are also a lot cheaper (than high end GPUs) to replace.

But if you have any free space within the case to suspend the GPU, or run the primary GPU outside of your case, it'll improve performance drastically.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby KA1J » Sun May 17, 2020 10:13 pm

So many helpful replies. The PC in my sig is the one I'm moving the fanless card to, or, I could switch computers. The computer I was planning on putting both cards into is an ASUS P8Z68-DELUXE-GEN3. An older computer with I think an i7-2600K. It is air cooled with a cooler Master 212 EVO. It is a big cooler and has push pull fans. It does have PCI 3.0 for both slots 16 solo and dual at 8/8

The idea of a PCIE x16 ribbon cable is new to me, I just looked at Amazon & see it but have no idea how to best use something like this. I'm not seeing how to get the card out of the case with this. It seems like twisting it to get it out through the back would kink it. There might be enough room to re-orient it in the case, I had to get the thickest case I could find to accommodate the oversize CPU cooler.

Maybe if I leave the side panel off the case it would make for better cooling?

Glad I asked, there's some things for me to look into. I'll have to see what I can find googling for photos of people mounting the card outside the case, that might be the best option. No problem to me to mount outside.

Thanks
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby JimboPalmer » Sun May 17, 2020 10:21 pm

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2 x PCIe 2.0 x16 (x16 or dual x8)
1 x PCIe 2.0 x16 (x4 mode, black)

So there are 3 PCIe x16 physical slots and you do not want to use the black one.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby MeeLee » Mon May 18, 2020 1:35 am

With core 21, using much lower bandwidth, it was possible to use USB risers.
The PCIE x16 ribbon cable I mentioned? Is a riser. It allows your GPU to rise up from the board by an x amount of cm (usually less than 20cm), and be tilted up or down (or diagonal, if you like); while still using the full 16 PCIE lanes.

With Core 21 it was possible to use USB risers. Basically a PCIE x1 slot, pushing data over a USB cable to the GPU.
The PCIE bandwidth on those is too low for Core 22 in most instances (unless the x1 port is PCIE 3.0, and you're running Linux, and the fastest GPU is not an RTX GPU or similar).
But a USB riser, is very easy to install, as you can just rout the cable very easily outside of the case.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby kiore » Mon May 18, 2020 1:58 am

My experience with RTX 2080tis unless you have a liquid cooled one is that they are hot and difficult to run next to a second gpu, I have tried extra fans the side off the case etc but nothing changes that these cards generate a lot of heat as well as science. I would consider using a riser for the less powerful card maybe the best option so even if you use the x 8 slot you can drop the 2nd GPU to where it would have been (or close) if you had used the x 4 slot and frequently this lower slot will squeeze you up against the PSU anyway. Miners dealt with the issues of running 6 or so cards by using frames and risers and for mining the loss of bandwidth not such an issue so there are a lot of riser cables around some better than others. I understand that a riser off a x8 slot may reduce it to x8 (- x) but still likely to be more than x4.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby KA1J » Mon May 18, 2020 2:44 am

Jimbo, yes, that's the board downstairs. Thanks, I won't use the black one.

MeeLee, I don't know if my processor/board is Core 21 or 22, not something I have known about, I've paid attention to reviews and bought the components that consistently did well review-wise at the time. I'm guessing both of my boards are probably not best using a USB cable so placing it outside the computer is not the solution. I'm not envisioning how the extender would help me, leaving the GPU in the case. If I attach an extender I can move it around in the case somewhat, but all the hot air would be blowing into the case. I wouldn't be able to move it to a farther away slot location and use that opening to shunt the hot air as the card would have to be upside down and it won't fit.

I guess what I can't envision most is how running the card inside the case, but in a different location would be cooler than leaving it in the socket to have it blow directly outside. Maybe it would be best to leave the sides off the case?

With the help, I'll get this worked out.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby kiore » Mon May 18, 2020 3:16 am

KA1J wrote:Jimbo, yes, that's the board downstairs. Thanks, I won't use the black one.

MeeLee, I don't know if my processor/board is Core 21 or 22, not something I have known about, I've paid attention to reviews and bought the components that consistently did well review-wise at the time. I'm guessing both of my boards are probably not best using a USB cable so placing it outside the computer is not the solution. I'm not envisioning how the extender would help me, leaving the GPU in the case. If I attach an extender I can move it around in the case somewhat, but all the hot air would be blowing into the case. I wouldn't be able to move it to a farther away slot location and use that opening to shunt the hot air as the card would have to be upside down and it won't fit.

I guess what I can't envision most is how running the card inside the case, but in a different location would be cooler than leaving it in the socket to have it blow directly outside. Maybe it would be best to leave the sides off the case?

With the help, I'll get this worked out.


The core 21 /22 referred to the GPU project type which act somewhat differently. Leaving the sides off the case if you can seems a good idea when running multiple GPUs even what are designed as high airflow cases frequently do not imagine the kind of use folders put their cards to.
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Re: Adding a 2nd Nvidia GPU - any head's up?

Postby KA1J » Mon May 18, 2020 3:18 am

Kiore, I remember hearing back in the day, that the length of the bus to the CPU was critical to speed, even to the dimensions within the processor itself. I left the tech back a long time ago & haven't kept up with what's current. I have been thinking the GPU was essentially separate from the CPU, and the WU's done by the GPU weren't dependent on the CPU or the bus. From what I'm hearing here, that's not true, that there's a significant difference the bus makes.

I'm still confused about how moving a card via a riser, to a new location, and not having it vent to the outside, would be better than leaving it in place and venting directly outside.
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