This might be a dumb question but...any issues connecting some GPU's directly on the motherboard and some using risers?
Most mining rigs I see in the internet either have all their gpu's connected on the motherboard or all via risers.
I'm planning to use Asus Z370-E for my rig.
You have to understand how a GPU is powered.
Some power come from the PCI-E slot (75W max on PCI-E 16x slot) and some power come from the 6/8 pins PCI-E connector(s) of the GPU.
The motherboard is compatible with SLI/Crossfire, so at least using 2 PCI-E slots directly is totally fine. Because it's design to give power simulteously to 2 GPU from the PCI-E slots.
If you want to use more GPU, you have to use powered risers (like USB risers) so the power draw that the GPU expect from the slot will not come through the motherboard (and it's a good thing, because it will not be able to safely provide so much power to 4-6 GPU on the slots).
The power will come from the risers with the molex or sata power cable directly from the PSU.
Do not use to much risers on 1 PSU cable.
For exemple, if you have 1 SATA cable from the PSU with 5 SATA plugs ... do not plug 5 risers, be cause it could stress this cable.
I prefer to have max 2 risers per cable on the PSU
Okay I see. I will have two separate 850w PSU's to power eight 3070. I'll make sure to distribute powering the risers between the two psu's. Thanks!