Hello All,
New Vray user here. I am currently running a single RTX 3090 and have been for the last 3 years. I’m considering either adding a second to improve render time (my main goal) or investing in a pair of a newer series of nvidia cards again to improve render time. I wanted to get a better idea of
what to expect from anyone who has had experience using 2 GPU’s with Vray for Rhino. 
Hi @Reederdzn48_gmail.com and welcome to the forums!
I suggest waiting for the upcoming Nvidia GPU generation in 2 weeks from now, most likely they will offer double the performance of the current GPUs in the market.
V-Ray GPU is able to use multiple GPUs with near linear scaling, if you add a second 3090 you get double the performance of what you have now. Please check this article about multi-GPU scaling
You will need a big enough case to house 2 GPUs, 1200 Watts power supply at least and a motherboard that could handle 2 GPUs with enough spacing between them. If you right me your system specs I will be able to help
Best,
Muhammed
I can only confirm that Multi GPU works wonderfully with Rhino, the performance scales as expected. The CPU should not be too lame when it comes to feeding multiple GPUs. I think the CPU load also scales roughly linearly. What do you think @Muhammed_Hamed ?
Thank you both very much for this! @Muhammed_Hamed I just sent you a message with my specs for us to discuss