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My system is 3090 Ti (24gb VRAM), 32gb DDR4, i7 8700k, Windows 10.

I've upgraded GPU recently because 8gb of VRAM on my old one wasn't enough, causing out of memory use or crashes in heavy scenes. However the new GPU acts similarly in heavy scenes, it crashes at around 14-15gb use of VRAM. It never uses all 24gb of VRAM.

The theory I've read online is that I need to have twice as much RAM as I have VRAM because of some Windows hard lock. So I need 48gb of RAM apparently? Could this be true and is there a way to unlock VRAM without upgrading? Task Manager shows I have 24gb of dedicated GPU memory, 16gb of shared GPU memory and 40gb of total memory. Why can't Blender use more than 16?

I render in Cycles: OptiX. My previous GPU 2070S 8gb was able to fully utilize all it's VRAM with scenes going up to 8200mb in VRAM use.

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    $\begingroup$ I would try updating GPU drivers and trying it with "Factory settings" (File -> Defaults -> Load Factory Settings, maybe backup your preferences first or be really careful not to save default preferences on top of yours, make sure that autosave preferences is off). Some addons may mess things up. Also if you are observing the VRAM usage using some other software, it might not be reporting it correctly. I would also try if not using the CPU as CUDA or OptiX device together with the GPU makes a difference. $\endgroup$ Dec 12, 2022 at 14:16
  • $\begingroup$ I've already eliminated CPU from rendering devices. Latest GPU drivers and latest 3.4 Blender. Do you mean factory settings in Blender? I tried it just now. At 16656.20 mb it gave an error: "System is out of GPU and shared host memory". Task Manager showed about 17gb of dedicated GPU memory use at that moment. $\endgroup$
    – blankpins
    Dec 12, 2022 at 14:27
  • $\begingroup$ Addons can have a huge impact it's worth trying without any addons loaded that's why I suggested Factory settings. Let's say new add-ons using Stable Diffusion... Anyway, so 17 out of 24... Might it be possible something else uses VRAM? Do you have Photoshop or some other software using GPU acceleration running, maybe software that might use AI? Task manager may show incorrect amount. $\endgroup$ Dec 12, 2022 at 14:58
  • $\begingroup$ I have Chrome running. 3 displays connected. Those never stopped 2070S from utilizing all 8 gigs of VRAM. $\endgroup$
    – blankpins
    Dec 12, 2022 at 15:23
  • $\begingroup$ I know nothing about GPU issues, but it might be worth checking if Linux has the same issue (you may need to install the latest NVidia drivers). $\endgroup$
    – tobiasBora
    Dec 12, 2022 at 17:54

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Ok I bought 64 gigs of RAM and now Blender project uses all 24gb of VRAM. This issue should have been better advertised.

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    $\begingroup$ Can you confirm that was the problem? have you solved all the problems related to "Out Of Memory" I'm having the same problem with RTX 4090 24GB and 32GB Ram On the motherboard $\endgroup$
    – Noob Cat
    Mar 5, 2023 at 17:23
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    $\begingroup$ You need 64 to utilize your GPU fully. It's unclear whether it's some Windows requirement or if Blender uses memory inefficiently though. But I can confirm that if a scene uses up to 20-24gb of VRAM the RAM usage jumps to 40-50s GB of RAM. RAM is necessary. After I upgraded I almost never run out of memory now. $\endgroup$
    – blankpins
    Mar 7, 2023 at 5:06

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