How does Daz Studio / Iray manage vram limitations?

jays222

Hello, I've read many posts, but it is still unclear to me how current versions of Daz/Iray manage when a scene needs more Vram than is available (using recent software/hardware). For example, if I have a scene that ends up needing 10 GB of GPU vram, and I only have 8 GB, will the render:

1. Recognize there is not enough vram before the full rendering process begins, and switch to CPU for rendering? Or:
2. Try to render, then eventually fail at some point? Or,
3. Render what it can using GPU, then switch to using CPU and complete the render?
4. Or?

I can't investigate myself because I'm on a Mac M1, and I'm considering purchasing a Windows laptop (for various different uses, and I understand it won't be like a desktop). I would guess that most of what I do would typically come in at around 8 GB vram usage, and maybe with various optimizing techniques I might be ok. But it makes me nervous because I don't want to buy a new laptop with 3070 ti, only to find out the GPU simply won't work at all in DAZ/IRAY on larger than 8 GB scenes. I'm less concerned with speed, more concerned with the GPU working at all for my Daz scenes.

It's frustrating that 3080 and 3080 ti are the only laptop GPUs I can find that have more than 8GB, and those laptops are almost twice the cost of a 3070 ti laptop. I've read about 800,000 reviews on how many fps these GPUs can do and which to choose for gaming, but that doesn't help me out very much. If anyone knows how the vram limits are managed in Daz, and if there are any laptop users with experience with the above mentioned laptop GPU's, that would be greatly appreciated. Thanks!

hansolocambo

only to find out the GPU simply won't work at all in DAZ/IRAY on larger than 8 GB scenes

the GPU won't work at all in Iray if the scene uses more than 8GB of VRAM. That's just how it is. Iray ain't hybird CPU/GPU. It's one or the other.

Render what it can using GPU, then switch to using CPU and complete the render?

Iray will switch to CPU if VRAM ain't enough and if you ticked the option Allow CPU Fallback in Render Settings > Advanced.

I would guess that most of what I do would typically come in at around 8 GB vram usage

I went from RTX 3070S 8GB, to an RTX 3090 24GB and the difference is huge (in terms of what that much VRAM can do, on top of course of how more insanely powerful the card is).

8GB is limited, but fine. As long as you use something like Ultimate Iray Skin Manager or tweak manually the shader, to create an infinity of different looking skins out of a unique skin applied to all Genesis. 

It all depends on what you are going render.

N.B : If you're short of cash, desktop computers generally offer better value than laptops with similar specs. I've never bought a laptop as I enjoy more power, 4 or 5 screens, a large Graphic drawing tablet, etc. I never understood how a 3D artist can work with something as small as a laptop... You should go for desktop and spend the difference in a card with 12GB at least.

PerttiA

First of all, if one has a GPU with 8GB's of VRAM, one doesn't have 8GB's of VRAM for Iray rendering as the baseload of W10, DS, the scene and the needed 'working space' already reserve almost 4GB's of VRAM (on an RTX card, GTX is even worse)

The DS log hasn't shown geometry and texture usage since DS 4.15 (which I still use), but from a DS 4.15 log, one can see that when preparing to start the rendering, VRAM is taken in stages, that is why some VRAM may be taken for geometry even when the rendering drops to CPU due to not having enough VRAM left for the textures.

jays222

thank you for the replies. seems like having hybrid GPU/CPU rendering (both available to work on a scene together), would be a serious game changer for many if not all Daz Studio / Iray users. Assuming thats possible... Even if just to have the ability to render larger scenes without the nightmares i'm reading about black screens and errors when running out of vram in daz, fallback, etc. 

PerttiA

jays222 said:

thank you for the replies. seems like having hybrid GPU/CPU rendering (both available to work on a scene together), would be a serious game changer for many if not all Daz Studio / Iray users. Assuming thats possible... Even if just to have the ability to render larger scenes without the nightmares i'm reading about black screens and errors when running out of vram in daz, fallback, etc. 

In general, enabling both, the GPU and CPU as rendering devices, has very little if any benefit in rendering speed, but often makes the computer sluggish while rendering.
Enabling fallback to CPU on the other hand, allows the rendering continue with the CPU when the GPU doesn't have enough VRAM. 

Gordig

I looked up my results from the benchmark thread:

A5000: 15.14

A5000: 15.08  + RTX2060: 4.80 = Combined: 19.85

A5000: 14.93  + RTX2060: 4.75  + 3960X: 1.20 = Combined: 20.69

That means that adding a low-end GPU (2060 Super) to the second-most-powerful GPU on the market at the time (A5000) bumped my iterations per second up roughly a third over just using the A5000, while the benefit of adding one of the most powerful CPUs on the market (Threadripper 3960X) was negligible.