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I recently found a motherboard that accepts up to 8 graphics cards (and therefore GPUs) directly, without the need for riser cards etc. It is marketed as a Mining computer for mining Bitcoin etc., but it struck me that if you could plug in say 8 GTX1080s (or whatever used Nvidia cards I found on eBay), then it could also be a pretty meaty renderfarm.

Does anyone know whether Blender would access and fully use all those GPUs if it was run on such a system?

The motherboard in question is marketed as "Biostar TB250-BTC D+ LGA1151 SODIMM DDR4 2400 8 GPU Support Mining Motherboard" and is not very expensive. Other, similar motherboards are available. The actual board isn't important, it's whether Blender would fully utilise the GPUs.

[Added 3 January 2020] I have also seen motherboards with about 16 smaller PCie slots, and cables that convert these into the full-size PCie slots. The idea being that more graphics cards can be connected into a rack using the cables. Would it work if an NVidia card was connected via one of those?

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  • $\begingroup$ Just wondering if you had a chance to try this idea :) $\endgroup$
    – user1566515
    Commented Nov 27, 2019 at 3:36
  • $\begingroup$ Not as yet. Due to other commitments, I'm not likely to be able to try it until some time mid-2020. $\endgroup$
    – Phil Rogers
    Commented Nov 28, 2019 at 11:13
  • $\begingroup$ Thank you. This sounds like a good idea. Hopefully we can get some comments here from people who tried it. $\endgroup$
    – user1566515
    Commented Dec 1, 2019 at 23:10

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Judging from Blenchmark, yes. I realize that it has been closed down for a while so its results should be taken with a grain of salt, but I don't think they're completely irrelevant.

Blenchmark

The mobo you posted should work fine if you don't intend on using anything too powerful/modern. The PCI-E 2.0 slots may bottleneck the GPUs connected to it if you connect them to GPUs that have been designed with higher bandwidth PCI-e slots in mind.

enter image description here

As far as the smaller PCIe slots and connecting cables go, I don't think you'll get 16 GPUs hooked up to that. What is most likely going on is that multiple slots are connected to a single GPU using those cables. I'd also be wary of potential hardware/driver issues when doing so. However, I'm not familiar with that subject, so keep that in mind.

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  • $\begingroup$ Thanks for that. The actual motherboard that I quoted was just an example. It's the principle that I was asking about. If I go for it, I'll look for a board with higher spec PCI-E slots. Sadly, finances don't permit me experimenting with it at the moment, but should do later this year, in which case,I'll add my findings to this thread. $\endgroup$
    – Phil Rogers
    Commented Jan 3, 2020 at 17:38
  • $\begingroup$ Just don't go pushing it too far. Remember that every extra GPU you add will be reducing render times by less and less. If your original render time is 100s, the second GPU (assuming all the same), will cut down to 50s, the third to 33s, the fourth to 25s and so on. $\endgroup$
    – stphnl329
    Commented Jan 3, 2020 at 17:41
  • $\begingroup$ That makes sense, but I often create animations which can take a couple of days to render on my lowly machine. If I can get that down to just one or two complete renders in a day, that would be useful. As it happens, since I posted the original question, Blender has moved on. Cycles is faster, and Eevee is astoundingly fast and works well for test renders before committing to a final Cycles render. $\endgroup$
    – Phil Rogers
    Commented Nov 20, 2020 at 12:10

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