I'd have to say that IRAY simply needs to do more calculations with displacement, it takes a long time with photo real mode. it really depends on what part of Iray you want to use because if you enable everything it will be slower.. also having iClone with high render mode while iray tries to  do it's own thing  will slow it all down . I'm using an RTX 2080Ti and it can take a day for say 300 frames..  (also had other things open) I did have a second card but the latest nvidia driver messed up CC3 and iclone  from being able to load. I  have a different approach to foam that I'dd be trying later, probably when I make surf waves.



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I'd have to say that IRAY simply needs to do more calculations with displacement, it takes a long time with photo real mode. it really depends on what part of Iray you want to use because if you enable everything it will be slower..

Yes, displacement would put some constrain on render, but not to such a scale. It is a bug. Pls. see my update to the original thread.

It might be a bug, better be a bug that means when fixed all this render time will be a lot faster.. I think that's what the new NVidia driver was about - faster rendering especially with RTX cards but again, there is a bug because it currently doesn't work with Reallusion software.

Our first product "Photorealistic Water And Wave Maker"  Store Page Link 
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i7 -4790K 4.0GHz | 32 GB | 2x GeForce RTX 2080 Ti 11GB | GTX 970 x4 | Window10 | Zbrush 2020 & Keyshot | Maya 2014 | Adobe CS6 | Sonar Producer X3 | iClone Pro & 3D Exchange Pipeline 7 | DTS Master Audio Suite | Perception Neuron 32 Alum Edition | Akeytsu

It might be a bug, better be a bug that means when fixed all this render time will be a lot faster..

Well, it is a little different bug not related to NVIDIA drivers. When they apply a fix, Iray would render with *normal* speed those scene featuring props with displacement a glow maps textures:
https://forum.reallusion.com/424475/Glow---Displacement-maps-delay-Iray-renders-exponentially

for me this is what iam looking for