Hi, I’m using vray hair/fur to soften clouds. I’ve got these scanlines that started appearing when using multi gpu in vantage and it appears to be hair/fur causing it. Here’s some examples:
This is in 2.3 with 551.86 driver using a 4090 and a 3090
happens at a certain threshold between per area density and hair thickness - depending what object it’s applied to
Do you see any warnings in the log ?
Something that starts with “VRayFur hair generation”.
Greetings,
Vladimir Nedev
hmmmm… lemme look and see
Here’s the two warnings that appear:
08:01:37.968 Warning: Disabled light cache because it produces artifacts in multi-GPU setups.
08:01:37.968 Warning: Disabled RTXDI resampling because it’s not supported on multi-GPU setups.
Only hair warnings that do come up, if any, are limits on the 50million strands enabled by default. However, I can’t see those scan lines appear on anything other than dense hair/fur
Here’s a simple scene that does it: https://wanderplay.com/stuff/Vantage-MultiGPU-VisibleScanLines.vrscene
Let me know if this helps -T
Is this with the latest Vantage update?
I tried on 2 RTX 8000s and don’t see the issue.
Is there anything I have to do after opening the scene ?
If it’s possible, can you send me the vantage.ini and defaults.vantage files from %appdata%/Chaos Group/Vantage.
This way I can test with the exact same settings. Also if you have a specific .vantage file for the scene.
Greetings,
Vladimir Nedev
I don’t know if I’m correct or wrong but you’re using two GPUs with two different architectures. RTX GeForce 3090 is based on the Ampere architecture, which features Nvidia’s second-generation ray tracing (RT) cores and third-generation Tensor Cores and the RTX GeForce 4090 is based on Nvidia’s Ada Lovelace architecture and feature Nvidia’s third-generation RT cores for hardware-accelerated ray tracing (RTX), and fourth-generation deep-learning-focused Tensor Cores… Let’s not forget NVLink is no longer supported on the Ada Lovelace GPU architecture that powers Nvidia’s flagship RTX 4090 GPU.
I’d suggest you to try to render with only one GPU but not with one disabled, try to remove it from the mobo and see if you encounter these scanlines.
These days Multi-GPU is more a pain than a gain, that’s why I have opted and bought a RTX 6000 Ada and frankly Vantage works like a charm, 8K renders are no longer a dream 
You may not see the issue because you’re using two RTX 8000 which are based on the Turing architecture and they support NVLink…I’m not 100% sure but from my past experience with the GPUs I might be right.
It will certainly work because these are multi-gpu artifacts for sure. No need to touch the hardware - we have device settings in Edit->Render Devices.
The fur shouldn’t be that much different on the 3090 and 4090.
It looks completely different on one of them in his renders.
We don’t have that setup however to test easily.
Greetings,
Vladimir Nedev
Hey Vladimir, I can look for those two files and email them to you. If/when occurs again I’ll pack a scene for you to look at. Thanks!
Here you go:
I sent the scene for this along with the ini and vantage defaults through support ticket number 243962
Hope this helps! -T
Thank you for the files!
The issue was reproduced successfully here.
We’re experiencing a similar banding issue using two RTX 6000 Ada cards on our workstations. We’re not using fur in our scenes, but we are using ForestPack, though the issue seems to be across the full scene rather than isolated to a specific object. I’m currently resorting to disabling a card to get clean results, but it would be great if there’s an alternative solution that doesn’t involve waiting for a patch.
Edit: Well disabling was a wash, it seems like I’m still getting the lines even rendering on a single card, any ideas as to what’s causing it? It’s particularly noticeable in clouds.
Can you send the scene to support so we can debug it ?
Greetings,
Vladimir Nedev
Sure thing, I’ll archive the file tonight and get it over first thing in the morning along with the most recent Vantage config I’ve tried.
@anthony_billet which denoiser are you using?
the issue seems to be across the full scene
The screenshot only shows clouds. Does it happen with actual geometry? Can you show an example other than clouds?
We’ve reproduced this and are preparing a fix. Just to clarify: it has nothing to do with the fur issue or multiple GPUs.