ETH Mining with Dual 1070 GTX in SLI and Overclocking 57 - 60 MH/s

Mining Ether is all about GPU speed and power! With the performance we were getting from one single new Overclocked 1070 GTX of nearly 31 MH/s, the only next logical thing to do, is Double It!

Adding a second GPU brings with it a few concerns though, it's not as straight forward as plug and play, although it could be...

Dual SLI 1070 GTX Nvidia GPU

First you need to make sure your Power Supply Unit is up to the challenge of powering 2 high-end GPUs like that, I'm using a Corsair AX860, 860 Watts Platinum + certified efficiency. The PSU needs to have the various 8-pin or 6-pin, or 6+2 pin cables required per GPU.

The next question will be HEAT, do you have adequate airflow and cooling to handle the heat that will be generated from two cards? because it's a lot more heat than just one card. Try to space the GPUs out as far away from each other as you can, when you're mining the number of PCIe Express lanes a slot has doesn't matter, as long as the GPU fits it will work.

~Pseudo-Related: Dip Your Toes into the Data-Lake of Knowledge Exploring Data-Science.

Unfortunately, if you have no choice and need to stack one card on top of the other, be prepared to see temperatures in the 80 C range for the card directly above unless you have really really strong cooling. Think box fan big cooling and or an Air Conditioner running nearby. The max safe temp for these GPUs is technically 93 C, but you will notice it starts to thermal throttle the core clock speed around 83 C.

Fortunately for us, the thermal throttle-reduced GPU core clock speed and voltage doesn't seem to negatively impact hash rate at all. Unlike the previous 980 GTX which was sensitive to both Core and Memory speeds, the 1070 seems to only depends on Memory Speed for Hash Rate performance.

There's also the question of to SLI or not SLI. I actually tested both, I tested the performance, heat and hash rate speeds with the SLI bridge connected/setup in NV control panel, as well as without the SLI Bridge and just two separate cards. I found I was getting better performance overall, smoother operation, and more controlled processing power by letting the cards run in SLI.

When you add a second card to your mining rig in windows 10, there's no changes to be made to your BAT file, everything should pick up automatically.

Once we got up and running with both 1070 GTX GPUs in SLI and began running Ethminer, the heat was so immense, the top card always hit about 80 C while the bottom card stayed around 50 C. The impressive part though, was that we were now hitting 50 - 53 MH/s while mining Ether.

Overclocking Dual GPU Nvidia 1070 GTX SLI using NVinspector

A small amount of tweaking and overclocking goes a very long way when you have two GPUs. Using GPUz for monitors and NVIDIA Inspector (Version # 1.9.7.8), I downclocked P0 GPU Core Speed by negative -200 MHz, to now run at around 1700 MHz, and testing yielded zero performance losses, but some heat savings by a few degrees C.

GPUz Monitoring Temperature and Speed of Dual 1070 GTX SLI Ether Mining

Further tuning put the Memory Clock Speed and PLUS +360 MHz, pushing out 4158 MHz, that's 8316 MHz in box label speeds, and now we are hitting 55 - 57 MH/s all day all night long with the bottom GPU at a cool 50 C and the top GPU and an almost marginally uncomfortable - but not technically bad - 78 - 80 C.

55 - 57 MH/s, Hash Rate Ethminer using Dual SLI 1070 GTX

There's one more thing you can do though; download "Nvidia profile inspector" version 2.3.1.6 or newer, as per some advice I read earlier, tested and now explain here. Rather than try to use offset to compensate for the GPUs not switching from P2 to P0 while mining, you can modify a profile and force it to run on P0, then you have more control while overclocking. Below is the original Reddit post I followed which worked for me. Now I am averaging 58 MH/s with spikes above 60 MH/s.

The Next Steps: How Profitable is Mining Crypto-Currency?

[–]T2098Strix 1070 + Windforce 7950 8 points 5 days ago 

When running general purpose compute tasks, Nvidia cards are set to underclock the memory by about 200mhz from the 'regular' clocks to ensure accuracy - this is by design and not just for the 1070.

If you want to stop this from happening, you can install "NVidia Profile Inspector" and under section 5 ("Common") you can set "CUDA - Force P2 state" to "Off" which will stop the memory from underclocking by 200mhz when running CUDA apps.

Alas, I don't have a link right now, but you must have version 2.1.3.6 or higher - most of the copies of NVidia Profile Inspector floating around (especially the ones bundled with the regular Nvidia Inspector) don't have the option to change the Cuda P2 state.

Ethminer Dual SLI 1070 GTX Nvidia 60 MH/s