I have the following hardware configuration:

PSU: Corsair HX1200i
CPU: Inter Core i7-6800K 3.4 MHz
GPU: NVIDIA GTX 1080Ti (Pascal)
RAM: Corsair Vengeance (DDR4) 32GB, 2666MHz
SSD: M.2 Samsung 960 500 GB
Motherboard: ASUS SABERTOOTH X99

And, I wonder, would it be simple to extend this system with 1 extra 1080Ti GPU?

As I know, the motherboard should be capable to provide x16 lanes for both GPUs. Though probably I'll need another PSU, and I am not sure about CPU.

  • If you run the numbers through online calculators, you'll find that the system would draw ~750W with two GPUs, so your 1200W PSU should suffice. As for the CPU it has 28 PCIe lanes, meaning you probably get the performance of 12-ish lanes per GPU (which is more than enough). – SEJPM Oct 8 '17 at 10:21
  • @SEJPM Ok, I see, thank you. And, could you tell me please, what if I am going to use the GPUs to train deep models? Would it be a problem to have only x12 lanes per GPU, or it could only affect initial data loading process into video memory? – devforfu Oct 9 '17 at 7:49

Your power supply is plenty. It can supply up to 1200 watts and your whole system will definitely not pull more than that, even with two graphics cards. Nvidia recommendation for GTX 1080 Ti is 600W PSU for the whole system, when using 1 card. You can also check that with some online calculators, for example this one: http://www.coolermaster.com/power-supply-calculator/

As for PCI Express lanes, I wouldn't worry about the lack of x16 lanes. Your CPU has 28 lanes, which means one of the cards will be running at 16x and other one at 8x (due to PCI Express specification), if you do not have any other devices that take up PCI Express lanes. Benchmarks and tests have been done by many tech reviewers/magazines, a GPU running at 8x will not decrease your performance in any noticeable way (up to 1-2 FPS).

  • Yes, agree, I've seen a couple of them and it seems there is no too much difference in rendering apps. But do you think the same is true for, e.g., CUDA computations? I don't know if this process is similar to rendering from memory manipulation point of view. – devforfu Oct 10 '17 at 7:36

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