Will more RAM help me render big scenes?

lukon100

I have only 16 GB of motherboard RAM.

Some big scenes won't use my GPU and get sent to the CPU instead.

If I increased my motherboard RAM to 32 GB, will this anable my GPU to be used on these bigger scenes?

Or...

Does the RAM have to be bigger on the GPU itself instead? - such that I must replace the GPU.

margrave

Only VRAM, the memory on your GPU, counts.

Best way to render big scenes is to buy Scene Optimizer and start cutting down texture maps. Even reducing them to 2048x2048 will reduce the memory used by three-quarters.

PerttiA

margrave said:

Only VRAM, the memory on your GPU, counts.

Not true, attached you can see a test I made for another thread, where I was testing the usage of RAM and VRAM before, during and after rendering with Iray.
Case a) One lightweight G8 figure with Lightweight clothing and hair
Case b) Four similar figures with architecture
Case c and d) started increasing SubD to see at which point rendering would drop to CPU

Togire

As it has already be said, VRAM is the most important, but it is not sufficient. You need a large amount of CPU RAM to fully exploit VRAM.

According to the results given above by Pertia, or many other sources (see for instance the video below where one cannot use more than 17GB out of a 24GB 3090 with 64GB RAM), you need at least 3x or 4x more RAM than VRAM. It varies from scene to scene but 3x seems a minimum.

So if you have a GPU with 4GB VRAM or less, adding CPU RAM will not help. If your CPU is 8GB or more it will help.

And increasing the GPU VRAM size does not really help with 16GB RAM. For instance, if your GPU is 4GB, you will see an improvement with a 8GB GPU, but not so much (except for speed of course thanks to a more recent GPU). Probably you will not be able to use more than 5 or 6GB of VRAM with 16GB CPU RAM.

richardandtracy

On my 6gb GPU, I generally top out at 3 characters. With one image I got 7 characters, but that was because they all had the same textures. I have also found bumping the RAM to 24gb from 16gb has slightly reduced the number of times a render dropped to CPU.