Quote from: pbfarmer on January 24, 2018, 04:38:56 AM

Quote from: shan23 on January 19, 2018, 09:46:56 PM

I'm a new comer to the forum, and I'm trying to get one last bit of info before I can assemble my 8 GPU rig. I was hoping you could answer my query regarding a similar setup.

I'm planning a 8 GPU build, in which I've ordered the following components:

2 x EVGA SuperNOVA 850 Titanium PSU
8 x GTX 1070 Founders Edition
Risers (6 Pin 006c as recommended in the wiki https://www.reddit.com/r/EtherMining/wiki/hardware/risers)

Here's a pic of the connections available in my PSU: https://imgur.com/a/j5TII

What I'm confused about is which slots do I connect the risers? I feel I have the following options:
1) Use a PCI-E splitter, so that each VGA slot is used by 1 GPU and its riser (got the idea from your aforementioned post)
2) Put each GPU in its own VGA slot, and its corresponding riser in a 6 pin slot in the same PSU (will have to use up a VGA slot for the third GPU)

Option 2 limits me to 6 GPUs in this rig, though my mobo is capable of 8 (z370-A). I'd obviously like to have a 8 GPU setup, but I don't want to use an option that is remotely unsafe. Am I being too paranoid about the whole thing (u can tell I read the Risers section in the wiki quite a few times!) ?

A cable w/ an 8 pin termination should be able to supply 150W according to the PCIE spec - if your GPU is drawing less than 150W, you should be able to split such a cable between the GPU and riser. The better option would be to simply use an 8+6 split (Y) cable - 8 pin to the GPU, and 6 pin (w/ an extender if necessary) to power the riser. That way you can be certain the cable is rated for that load (an 8 + 6 termination should supply 150W + 75W per PCIE spec,) assuming your cards draw less than 225W (which they absolutely should for mining.) Since you only get two of those types of cables w/ your chosen PSU, you could use the 2 x 4 pin peripheral (a.k.a. molex) cables to power your other 2 risers.

A couple other notes:

1. The draw on an 8 pin termination of a PCIE cable is spec'd to 150W, but the cable likely can provide closer to 180W (3 hot pins @ 5a x 12v or 60W each,) while the supply is actually probably closer to 240W (4 hots x 60W,) so you're probably fine just splitting a single 8 pin terminated cable if GPU TDP is < 180W. But if you want safest, the config above works (and saves you from buying additional splitters.)

2. The FUD around sata power is a little overblown. While a sata power connector easily provides the 75W max allowed for a PCIE x16 connector, the main concern is that the PCIE spec allows for 5.5a over the 12v rail (66W) on the MB connnector, while a sata power cable only provides 3 12v pins @ 1.5a each, or 12v @ 4.5a (54W) total. However, most modern, optimally tuned GPUs run around 75-150W for mining, so a single 8 pin PCIE power cable likely provides all the 12v power the card needs, w/ the MB connector/riser providing the 5v, and minimal (if any) 12v. Of course, this split is up to the GPU manufacturers, and they *could* technically pull all available (66W) 12v power from the MB bus before utilizing the PCIE power cable (or split as evenly as possible across the 2 sources,) but that is not how I've seen power delivery implemented on any recent card I've used. My cards all run in the 100-150W range, and the ones using risers powered by sata cables are doing just fine.

3. Ver 006C is pretty old for the risers. I would recommend at least ver 008s, like these: https://www.amazon.com/EXPLOMOS-Graphics-Extension-Ethereum-Capacitors/dp/B074Z754LT

Thanks a lot for the detailed reply - I learned quite a bit from it, and have ordered the 008 risers as per your recommendation!

Two follow-up queries:

You mentioned I could use 2 x 4 peripheral cables (molex) to power the other two risers (ones which aren't connected using risers). Did you mean that I use each of the 8 pin CPU ports in my PSU (marked as CPU1 and CPU2) for 2 molex cables (referring to the back of my PSU whose pic I've linked before)? If not, I don't see any more ports that are capable of handling the 4 pin Molex's?
I'm trying to get identical power inputs for each of my GPUs - so, I'm considering buying 2 more Y splitters ( 8 + 6 split(Y) to 8 pin) so that each of my 4 GPUS and its corresponding risers are powered using the Y cables. Is there anything wrong with that idea, other than the fact I'll have to order extra splitters? Speaking of which, I should be able to purchase EVGA splitters from the manufacturer's website, right, or would any amazon Y splitter would do?

Thanks!

shan23

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