Iray not using all VRAM before falling back to CPU
Reality1
Posts: 115
My system has a GTX 1070 with 8GB, but DS IRAY renderer falls back to the CPU when the texture, geometry, and lighting totals are about 3GB. My system is only one HD (1920x1080) display on Win 8.1 with no other apps running that are using VRAM.
I've tried rebooting, changing the texture compression settings, resetting render defaults, changing nvida settings for DS, so far no luck.
Any idea what's happening with the other 5GB? Is there someplace I need to allocate more RAM to CUDA?
Other settings I can change?
Known issues?
Daz 3D is part of 
Connect
DAZ Productions, Inc.
7533 S Center View Ct #4664
West Jordan, UT 84084
Licensing Agreement | Terms of Service | Privacy Policy | EULA
© 2025 Daz Productions Inc. All Rights Reserved.
Comments
Iray does allocate some VRAM to simulate RTX features on pre-RTX cards, and Windows is also using some of it to drive your monitor, but I can't imagine that accounts for all of it. Another user was having a similar issue which turned out to be caused by displacement. Apparently the extra "geometry" created by the displacement was eating up VRAM without being reported.
Thanks Gordig.
And yeah, 256mb should be enough to drive the display.
In the file I'm working with, it seems to be a smiple matter of threshold for the VRAM usage. I can get the CUDA kernel to start by removing some of the big tex, but I want them in the scene and I don't want to be limited to 3G when I have a 8G card.
Do you have Scene Optimizer? You could try removing displacement and normal maps. You can, of course, do it manually, but that might be a lot of work depending on what's in your scene. You could also give Camera View Optimizer a shot, if there are things outside the camera's view that are bogging the system down.
Iray rendering also needs "Working space" which it will adjust according to available memory, between 1-1.7GB and I have noticed that if the working space is around 1GB or less, the speed will suffer.
The attached chart shows VRAM and RAM usage and what the DS log was reporting (Geometry+Textures+Working space)
The OS and DS will also reserve some basic load, 200/170MB's in my case.
I'm running W7 Ultimate with 64GB RAM and an RTX 2070 Super (8GB), DS 4.15
The only way you can be sure how much GPU VRAM is being allocated to D|S is to check Task Manager. Lots of other software on your PC uses GPU VRAM. Under Task Manager/Details you can see which applications are using how much VRAM. The Iray log does NOT tell you what W10 has allocated to D|S.
Daz log does report the work space and frame buffer memory useage. Look in your log for something along the lines of
Allocated 189.844 MiB for frame buffer
Still 3+2 = 5 still leave some missing ram.
Ps: Daz dont free the workspace and frame buffer after rendering but it will be reused for subsequent rendering so it is wasted.
Not sure what point you're trying to make, but here are some actual numbers for Dedicated GPU VRAM used by D|S for a particular scene I rendered (based on Task Manager Details tab showing usage for the D|S processes):
This was confirmed in the Performance tab which showed about 3.5 GB VRAM usage across all processes.
Now, when this was finished, the Iray log gave these values:
Nowhere in the Iray log does it tell you that D|S was using over 3.5GB of VRAM during rendering. Not even close. That's because Iray does not decide how much total VRAM will be used by and allocated to DAZ Studio (not just Iray). That is determined by Windows 10, after the software apps like D|S and others make a request for their individual VRAM needs. And presumably they will also ask for more than they might need, to allow for changes as they run.