CPU ram usage vs gpu vram usage

sinatba81

hey there, i have been using an i3 12100 for iray rendering and usually at 5200p DS uses around 10gb of system ram, i want to buy a NVIDIA gpu and i want to know how much lower that 10gb ram usage can get when using the VRAM for rendering and how much VRAM will be used overal compared to system ram with cpu, thanks.

Richard Haseltine

It is hard to compare CPU and GPU use as the system memory holds the base scene data, and the data generated in preparing a scene description for Iray, plus the Iray data itself - and iray does thing in GPU that it doesn't do in CPU. Still, is this an absolute 10GB or an increase of 10GB over the use before starting to render? The increase in memory use would at least exclude the demands of the first block of data, the base scene data.

Padone

In general you can expect the gpu to use about 1/2 vram compared to the ram usage, that means on 10GB ram the gpu should go about 5GB vram. Then iray is very lazy handling vram and it tends to overshoot, so for example if you have a 12GB card then iray may allocate half of it or more, even if there's no need for the actual scene.

sinatba81

Thanks everyone for your answers, so it will be around 40% less than average system ram usage hah, i expected a number between 1gb to 2gb because optix and cuda stuff.

gram

yeah from what ive seen the ballpark seems to be that scenes use roughly 2x more system ram over video ram.

Naturally its not necessarily always like that; but in my use case most of the time thats what i see.

i have 4090 with 24g VRAM and some scenes easily eat up over 32+GB system RAM while vram stays below 20G.

For vram usage there are some options directly in iray options like the "texture compression thresholds" that may help. 

And theres at least one tool in the store here - scene optimizer which may help if you find yourself struggling.