Relationship of textures and GPU/CPU memory [duplicate]

Question

I am trying to transition from Eevee to Cycles on a very big scene.

I am using:

- Ryzen 7 2700 8-core
- 32 Gb RAM
- NVIDIA RTX 2060
- Ubuntu 20.04.01
- Blender 2.90.1

Eevee works
I am able to render with Eevee, and in fact have done 2 animations already using the scene. I didn't appreciate how much RAM would be required, but once all the textures are loaded they use over 70 Gbs of memory. In order to get the textures loaded, I had to increase the swap memory, but it does work. Each frame takes around 2 to 3 minutes to render.

Scene is optimised
The scene is optimised as best I can. I use instancing where-ever I can, turn off anything that is not visible in the scene, but short of a complicated re-structuring which would limit my flexibility, there is not much more I can do.

I plan to upgrade the machine to a 16-core Ryzen 9 128 GB RTX 3070, but before I do I want to see if it is possible to run the scene on cycles. I can't get the scene to load in cycles and I suspect it's because of not enough VRAM.

What I tried
I have tried Cuda, Optix, and CPU only. All of them crash Blender. If I load the textures with Eevee active and then switch to Cycles, the render kernels initalise and I then get the "out of memory" error. It seems to me that more (or all) of the scene is loaded into graphics card which confuses me. If that's the case, upgrading my system with plenty of RAM won't do anything, and even a $5000 quadro wouldn't load the scene.

What I don't understand is, I tried the scene on an older computer with 128 GB RAM using only an RX 560 ...only 2 GB RAM...on cycles and it did load. Very slowly...but it loaded. As I write this, I seem to be able to get an older version of the file open on CPU only. Does this mean I will not benefit from CPU/GPU rendering if I upgraded? I would be better off with a faster computer with as many cores as possible (threadripper) rather than a faster better GPU?

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Question
I really need advice on understanding the relationship of textures and GPU/CPU memory. Does anyone know of any resources that could point me in the right direction?

Answer 1

It depends on operating systems, kernels, and graphic driver, and blender version. It seems you are out of system ram. I think you may need a special build kernel or custom configuration kernel for better linuxing.

I think the cpu is processing the required data with sthe system ram than transfer it to the gpu to be processed with its own vram. It does that on my windows system, sometimes I get out of memory messages, sometimes its ok.