GPU Rendering Box?

J

jfharper

Limp Gawd
Joined
Mar 25, 2005
Messages
166
The advice from my fellow 3D guys is it's better to build a box with, say 4 GPUs, instead of two boxes with 2 GPUs each. They say it's more cost effective, but I'm having trouble finding a MB with 4 slots? Also, when the pciex speed is reduced with multiple GPUs, does that effect efficeincy?

Lastly, I'm trying to wrap my head around the PSU requirement and other factors for this type of setup. Can anyone offer some advice? TIA
 
It's not too hard to find motherboards with 4x PCIe 16-lane slots for quad GPU usage, so PCIe speeds are not necessarily reduced. Efficiency may be impacted if PCIe Switch IC's are used to provide those x16 PCIe slots.

The PSU requirements is heavily influenced on what you put inside that computer, such as the GPU and CPU. Without any additional info, we can only guess and say you need at least 1000w.
 
Power supplies:

Take the TDP of your processor and the TDP of your GPUs, add all of that together. Add 100 to that number for hard drives, fans, etc. Add another 10% to that number to account for PSU inefficiency. That's about what minimum size, in Watts, you need for your system without any overclocks. It will probably be smaller than you think, but also consider that power supplies degrade over time, so rounding up to the next couple of standard power supply sizes up will help with that.

Overclocking needs much more, it can exceed double that wattage on heavy overclocks.

If you start to get crazy, anything up over around 1200W and you need to start thinking about a dedicated power circuit or risk tripping the circuit breaker for the room once lights, monitors, peripherals, and everything else are all drawing on the same circuit. And anything over 1500W and you need to start thinking about high amp outlets or higher voltage (220 like in a dryer outlet, rather than 110 a typical outlet has available)

As far as inefficiency of reduced PCI lanes - depends heavily on the workload, but in general it's not too significant. And yes, it's possible to get motherboards with sufficient PCI lanes to keep from dropping below x8.
 
OK, thanks. Someone showed what MBs to look at, they explained the cpu lane requirment, MB, etc. Once I looked, I started figuring it out. Thanks for the info on the PSU, I'll do some calculations and see what I get. Thanks again.
 
I'd say take 300W for each GPU and CPU, and about 100-200W for the rest of the components.

Even if you're not gonna reach those figures, it still gives you a lot of headroom for later expansion and upgrades.

For a system like this I highly recommend using more than 1 PSU.
 
What type of rendering? Like V-Ray RT?

Here is a build and some sample results using 4 GPU's
http://dabarti.com/vfx/building-4xgpu-rack-mount-rendering-node/

Since V-Ray RT requires Cuda they need to be of course Nvidia cards. Now for PCIe lanes for rendering, I don't believe it has that much impact since virtually all the work is done on the GPU's themselves and just communicating the results back to the cpu. In other words you probably won't see much difference between 4x PCIe or 16x PCIe in performance.

Also you can go with the cheapest cpu as well since you will only be really using that with modeling and setting up the scenes.

Now if you are talking about video rendering with larger datasets then that may require way more PCIe bandwidth with of course the SSD bandwidth as well like in multiple NVme drives using PCIe. I really don't know there in the end.
 
If you want 4 x16 slots at native x16 speeds you are going to have to get a proper 2 cpu workstation board - an asus Z10PE or similar. Any 1 cpu board will have to use a PLX switch to give you give you the number of slots you need - however they will only run at PCIe3.0 x8 so that may limit what you are doing.

PSU wise if you are using 1070/1080 cards a 1200 watt PSU will be fine, if you are using cards with a 250w TDP, Titan, 980ti etc you'll need a 1500w PSU or 2 smaller ones
 
I personally like the EVGA PSUs at around 1500W with a single 12V rail.

Been using it for a few years now. Really good chance it'd be fine for 4xGPU and 1xCPU as long as he's not modding the cards for OCing..
 
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