Are mining systems suitable for use as a render farm? 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?
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.



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.



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.