Dual GPU
towdow3
Posts: 89
in The Commons
I cant remember the link to the chart that had render times. tested on dual gpus. I have a question however. When using dual GPUs do they need to be the same GPU. for example if i get an asus strix 2070 FE do i have to add a second asus strix 2070 FE or will any 2070 card work? Do i also need nvLink?
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The cards do not have to be the same as long as both cards support the version of Iray and driver used in your setup. I am using a 1080ti and RTX 2080ti side by side. NVlink is not supported or needed.
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TD
THANK YOU
You can use any combination of GPUs that Iray supports. You could even use a 2080ti and a GTX 750 together if you wanted.
The CUDA cores will stack and work together as long as the scene fits in each GPU's VRAM. Just as example, you have 3 GPUs, 1 has 2GB, 1 has 4GB and 1 has 8GB. If you make a scene that is 3GB then two GPUs that fit the scene will run and combine their efforts while the 2GB GPU will sit idle and do nothing at all. If the scene is 6GB then the 8GB GPU will be the only one that renders the scene.
So it is a good idea to have GPUs that have similar amounts of VRAM to ensure they always run, but that is totally optional.
you think its more constructive to have dual 1080ti than dual 2070s? im looking at this froma pure cuda core perspective bc most of my scenes have 4-6 people, mostly interiors.
That is really hard to say, because there are still many things that can effect how much memory you need. How complex is the interior? The clothing the characters wear, and their own textures and stuff, all of it matters. As does how large the render itself is. The smaller the resolution, the less memory.
The 2070 Super should be faster than a 1080ti now. The RT cores matter, but even without them the 2070 S should be about as fast or more. With them and 2070 S can go much faster. The 1080ti might have more CUDA, but the 2070 S has better optimized CUDA, so you cannot directly compare them. You can only directly compare CUDA counts with the same generation, so Turing to other Turing. The benchmark thread is in my sig. The person who posted a 2060 Super beat my times, so yeah, a 2070 Super will as well.
The only reason to look at a 1080ti is for the 11GB. The 2070 Super will be faster.
I actually have two 1080tis. I got the second one used before the Turing launch as the prices came down. Ebay also had a great deal that day to saved me like $80 off the price. I do sometimes use a pretty good amount of that VRAM, as I have seen it report 9+ GB usage in MSI Afterburner several times. I think I had 6 figures, so its really funny you actually said 6 figures in your post, and talk about 1080tis, as I have done both, LOL.
But I did not super optimize things. You can use Scene Optimizer and other tricks to cut down on VRAM needed. If you have 6 people, you probably don't need HD morphs and textures because the camera is probably zoomed out a bit.
hhmmm. im, considering sellingmy 2070 bc i have this scene for example and i let this run for about 45 minutes and still wasnt done. I hadnt bothered optimizing either. that 11gb of vram on the gpu is very sexy bc i feel like 8 isnt enough.
Huh ? I called Nvidia, rep states cards have to be identical.
They do not. i have a 2070 and 1080ti both render together just fine. You need identical cards for SLI in games.
It's highly unlikely you'be able to get 1080ti's for any sort of reasonable price. Even the used market is pretty pricey ($500 roughly on eBay).
This.
SLI hardly has any effect on iray anymore.
And for SLI you also need a motherboard that supports it.
And the only GPUs out of the RTX line that have SLI support are the 2080's, so it looks like SLI became mostly obsolete and is going to be discontinued anyway.
So, overall, don't bother with SLI, ignore it completely, and be glad that iray works with any combination of GPUs provided they share the same version of driver and iray.
As for the 1080Ti vs 2070 for iray: the 1080Ti's have the benefit of larger VRAM, which means more complex scenes can be rendered with these. However, the 2070's are noticably faster in iray.
Gaming is an entirely different story, the 1080Ti's are generally still better there, especially at 1080 pixels width, unless a game makes use of raytracing. So gaming benchmarks and iray benchmarks aren't really comparable, they diverge quite a bit with the addition of the 20xx series.
The VRAM only makes it faster if you run out of VRAM on a smaller card. Was this scene rendering on the 2070 then? Because if it was not, then ok, it might render faster on a 1080ti IF it fits in the 11GB. However, if this scene was rendering on the 2070, then a 1080ti will likely NOT be faster. So you would be wasting your time, and possibly money.
If you already have a 2070 then I would not make the effort for a 1080ti. It will be slower in any scene less than 8GB. As I said, the one and only reason is if you truly need that extra 3GB a 1080ti has. At this point I would instead focus on optimizing the scene. You are at a large distance from the characters here. So what you can do is resize and/or compress most of the textures for them. You could probably make them quite small and you wont see any difference. Plus this bonus, optimizing will speed up render times regardless, so doing this will speed up rendering even if it already fits in VRAM.
Since you talk about dual GPU, you could buy a 1080ti as your secondary card and have it render with the 2070. As long as the scene is under 8GB, then both cards will run. However, if the scene exceeds 8GB but not 11, then only the 1080ti would run. However, I am not sure I would really recommend this. You need to really think about how you want to tackle this. Honestly, I do not think there is a correct answer, it is going to be up to you to decide what to do.
If you are seriously thinking about two 1080tis, then maybe another option would be ditching that thought entirely and going with a single 2080ti instead. Then you get the 11GB VRAM plus a much faster rendering card. We have seen a single 2080ti match two 1080tis in that benchmark thread. Yes, it is that fast. Obviously the price of a 2080ti is crazy high, but it is roughly the price of two 1080tis or 2070s. And given that it is about twice as fast, that sort of makes sense.
One last note, there are rumors about a 2080ti Super coming out sometime soon. If this is true then that could be, well, super. All of the Super cards have dropped the silly Founder's pricing, which has lead to an overall drop in price. So if a 2080ti Super is indeed released, it could release for $1000 rather than $1200. BUT this is only rumor, there is no confirmation it is actually true. Plus new Ampere cards are coming in the second half of 2020, though I can understand if you do not want to wait that long, that's nearly a year out.
Nvidia Iray does not use SLI. SLI requires the cards to be the same. But Iray can use ANY combination of GPUs that work with Iray. If you wanted to use a GTX 680 with a 1080, you can. I have used a 670, a 970, and a 1080ti together at different times, so I can tell you this is correct. If you spoke to a Nvidia rep, they probably only think about gaming. I bet that rep doesn't even know what Iray is, LOL.
Also, you can actually SLI different models together as long as they are the same chip. Like a 1080 from MSI can SLI with a EVGA 1080 as long as the SLI cable can fit them. With Turing the Nvlink connectors are are solid and don't flex, so you do need the cards to be the same in order for the connector to fit. But again, none of this applies to Iray which does not use SLI.
I learned from another thread to use your system RAM instead of VRAM if you run out, although it's obviously slower. Just turn off optix prime and max out the texture compression thresholds. Buying more system RAM so i can use 64 gbs.
so how does one use system ram as opposed to vRam? I've got 32gb right now.
Padone explains how in this thread: https://www.daz3d.com/forums/discussion/161526/how-to-use-your-ram-with-the-gpu-nope-just-a-bad-bug-in-the-log-please-daz-fix-it/p1
Padone admits his error in the title. iRay cannot use RAM for rendering.