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I have an NVIDIA Titan GPU and I'm able to add another card, but I wonder whether Blender will benefit from more than one GPUs?

Should I do it as SLI or should I just do it as an added card? I just need some help in understanding how Blender will use either SLI or a second GPU.

Note that I only use Cycles.

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There are lots of good articles out there on this topic, and short of recreating them, I can say that the two cards I use are not in SLI (wrong motherboard for it) and it uses them like two separate cores. It'll render two chunks at a time, if you tell it to use both. Some of the articles say that running in SLI is a little slower than running two separate cards, but I'm not familiar with the principles behind that.

I don't know if the rendered preview (in the viewport) benefits at all, but it can't hurt.

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Using more than one GPU will certainly speed up cycles. In user preferences->system->compute device you can configure which cuda devices to use (or ignore). When rendering, each GPU will render one tile (following the settings on the performance tab). The more GPUs, the more tiles being rendered simultaneously, so two GPUs will cut rendering time almost to one half. Other than rendering, only one GPU will be used for calculations and to refresh the screen. The memory accessible for rendering is going to be limited to that of the card with the least memory.

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  • $\begingroup$ I have a fairly new windows/gtx970 machine. Is it possible to add a second GPU ? Does this require also other investments (next to the GPU investment) ? By the way, this GTX970 has 2GB VRAM, I guess I had better opted for the 4GB ? Does this make a lof of difference ? $\endgroup$ – Old Man Mar 5 '16 at 23:37
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I have 3 cards, 2 cards scaled with a factor of 2.0, now the 3rd card scaled something along 1.7-1.9 factor. So 2 cards make a huge difference in cycles. You will for sure cut the render times in half.

All articles I've read suggest not using SLI for apps using CUDA/Compute. If you're on Windows you can via drivers enable it or disable it. It's currently not working under Linux AFAIK.

So turn it ON when gaming, turn it OFF when rendering with Blender.

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  • $\begingroup$ I don't know this word "SLI". I have a windows/nvidia machine, how do I know when this machine can have two GPU's and if this will bring me some Blender rendering improvements ? $\endgroup$ – Old Man Mar 5 '16 at 11:49
  • $\begingroup$ SLI is nvidias tech for gaming, I.e. it's a way to have 2-4 cards to act as one card. Improvs gaming performance. Nothing that really improves Cycles rendering performance. First you need to check what card you have, because optimal is to have same amount of vram, or more precise two card of the same type. Then just check that your computers motherboard have a PCI slot free and room for another card, and that your PSU can handle two graphic cards. $\endgroup$ – martinlindelof Mar 29 '16 at 15:26

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