This information was originally posted in some other threads. Thanks to everyone who helped putting those pieces together.
I repost it here in the form of a summary to make that information accessible without the need to read through a lot of other information.
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- What is VRAM and why does it matter when rendering with DAZ Studio Iray?
When you render with your video card (aka GPU - Graphics Processing Unit) all the geometry and textures of objects in your scene need to be loaded in the memory of the video card. This memory is called Video RAM or short VRAM.
- What happens when you do not have enough VRAM to fit the scene?
If the available VRAM is not large enough to fit all textures and geometry then Nvidia Iray will switch from GPU mode to CPU mode. This means your video card will not be used at all and rendering will be much slower.
- Where can you find information about VRAM directly in DAZ Studio without using 3rd party applications?
There are two different "logs" that you can check when you want to know how much VRAM is available to use for rendering with DAZ Studio Iray.
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1) The DAZ Studio log file
DAZ Studio creates an official log file that you can access
Help -> Troubleshooting -> View Log File...
The log file then should pop up like this:
If you search the DAZ Studio log file for the term "NVidia Iray GPUs" you will find the information about your system and installed video cards.
-> This will show you how much VRAM is installed as total and how much of that is available for use.
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2) The render log window
When you click on "Render" in the Render Settings tab two windows open if you choose to render to a window
- the "render window" will display the render in progress
- a "render log window" opens showing information about the render in progress
By default that log window may be hidden behind the render window.
-> Manually drag and resize both windows so you can see both properly while rendering.
-> This will tell how much VRAM is used for
Geometry memory consumption
Texture memory consumption
Lights memory consumption
Material memory consumption
etc.
-> If you add up all those values you know the memory consumption of your scene.
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Example:
Rendering in NVIDIA Iray
Compiling Shaders - 0/1
Rendering image
Rendering...
Iray VERBOSE - module:category(IRAY:RENDER): 1.40 IRAY rend progr: CUDA device 0 (GeForce GTX 1080 Ti): Processing scene...
Iray VERBOSE - module:category(IRAY:RENDER): 1.38 IRAY rend progr: CUDA device 2 (GeForce GTX 1080 Ti): Processing scene...
Iray VERBOSE - module:category(IRAY:RENDER): 1.39 IRAY rend stat : Geometry memory consumption: 36.14 MiB (device 0), 0 B (host)
Iray VERBOSE - module:category(IRAY:RENDER): 1.35 IRAY rend stat : Geometry memory consumption: 36.14 MiB (device 2), 0 B (host)
Iray VERBOSE - module:category(IRAY:RENDER): 1.35 IRAY rend stat : Texture memory consumption: 2.15994 GiB (device 2)
Iray VERBOSE - module:category(IRAY:RENDER): 1.35 IRAY rend stat : Lights memory consumption: 5.84766 KiB (device 2)
Iray VERBOSE - module:category(IRAY:RENDER): 1.39 IRAY rend stat : Texture memory consumption: 2.15994 GiB (device 0)
Iray VERBOSE - module:category(IRAY:RENDER): 1.39 IRAY rend stat : Lights memory consumption: 5.84766 KiB (device 0)
Iray VERBOSE - module:category(IRAY:RENDER): 1.35 IRAY rend stat : Material measurement memory consumption: 0 B (GPU)
Iray VERBOSE - module:category(IRAY:RENDER): 1.35 IRAY rend stat : Materials memory consumption: 1.01849 MiB (GPU)
Iray Iteration: 1
Iray :Render target canvas was written.
Iray Iteration: 3
Iray Iteration: 23
[...]
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How can you tell if Iray is currently rendering in CPU or GPU mode?
In the render log window search for an entry like this:
Iray VERBOSE - module:category(IRAY:RENDER): 1.13 IRAY rend progr: CPU: Processing scene...
-> If the word CPU shows up in your render log window Iray has switched to CPU mode.
How can you find out why Iray switched to CPU mode?
- Compare the entry “available memory” from the DAZ Studio log file to the entries Geometry, Texture and Light memory consumption in the render log window.
If the sum of the “memory consumption” is higher than the “available memory” Iray was switching to CPU mode as intended.
- Check both the DAZ Studio log file and the render window log for error messages.
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