A mining rig with seven GPUs

As I said using more than six GPUs in a GPU mining rig uncommon, why?

1. There are few desktop motherboards available that has more than six PCIE slots.

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2. Having six or seven PCIE slots does not make a motherboard: mining friendly, most of motherboards are not designed to have all PCIE slots occupied, they only offer different slot placements in different computer build configurations. Consequently, if you hook them with six or more GPUs, they don’t work or may not be stable.

3. The power draw of a GPU mining rig with more than six GPUs is close to maximum threshold of a single PSU, ~1300W-1600W, and using a second PSU is not so welcomed in modern designs of GPU mining rigs.

Any regular desktop motherboard that has 6 available PCIE lots and a M.2 expansion slot, can accommodate seven GPUs. MSI B250 KRAIT Gaming, Asus Prime H270-Plus, MSI Z270 SLI Plus, GIGABYTE GA-Z270-Gaming K3 or MSI Z270-A Pro are some examples of them. There are six available PCIE slots available on these motherboards, and the seventh GPU will be connected through M.2 slot. A PCIE 4X Female to NGFF M.2 M Key Male Adapter is being used to connect graphics card to the motherboard. Read more about it in this Chapter, in Accessories section.

However, Asus Prime Z270-A Gaming Mainboard with socket 1151, has seven available PCIE slots, so on theory there is possibility of connecting seven GPUs to this motherboard without using any M.2 expansion slots.

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Based on this motherboard, I have setup a seven GPUs mining rig of “Ex07-1151- Rev01” where you can find the details in the Appendix Chapter.

In a “Bits Be Trippin” YouTube channel, I have seen a build that this motherboard is being used to make a GPU mining rig with nine GPUs, connecting two of GPUs through M.2 expansion slots. In that particular build, rig draws ~1560W and makes ~264 MH/s with nine AMD Radeon RX 580 cards.

The other option on building a more-than-six GPU mining rig is using non-desktop configurations. In this case, we need to move to using a server-board machine. Server motherboards are those that have 7 available PCIE slots and usually come with dual CPU-socket configurations. This makes them more expensive. I recommend you use a socket 1366 motherboard because a socket 771 is too old with a DDR2 RAM and doesn’t come with the required PCIE lanes and performance, and sockets 2011 or 2011–3 cost more than $400 now, although these would also provide a stable and modern system.

If you have decided to try a 1366-socket system, always try to get a complete server computer rather than parts. The reason for this is that a server motherboard, especially the OEM version, has more complexity than a desktop machine, and may not be compatible with custom CPUs or RAM. In addition, the system requires a pair of CPU coolers as it has two CPUs (one cooler for each CPU) and some motherboards do not work with a single CPU configuration. The best option is always to get a used clean working server machine.

A Fujitsu PRIMERGY RX300 S6 [7] has a D2619-N15 GS1 motherboard, which costs ~€100 [8], although a complete system can be found from around €200 on eBay (link is here)15_{. The recommended RAM for a 7-GPU mining rig is 16 GB, and a}

server motherboard requires ECC RAM modules.

The good thing about server systems, which usually use Xeon CPUs, is that they have a lower TDP than desktop CPUs, and they also operate at a lower temperature. The RX300 S6 with two Xeon 6-core-X5650 CPUs (each CPU uses 95 watts on 100% load) runs on idle with 3 HDDs that use 136 watts [9]. The best socket, 1366, for a mining rig is Xeon L5609 with a 40-W TDP, or similar Xeons. You can choose from the Intel website [10], link is here The average power consumption would be 900–950 watts. So, with the “Ex07-1150-Rev01” system with 7 AMD RX 470 4GB GPUs, the total cost of the system would be ~€2150. With a

15 _{eBay links are not valid for a long time. Usually, they are available for a month. So, you will need to search with the} right search phrase, for example, “Fujitsu PRIMERGY RX300 S6”.

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value of ETH of $10.05, a difficulty of ~93.2 trillion, a power consumption of 950 watts at a cost of $0.1/kWh, and a hash rate of around 140–165 MH/s, the earnings would be ~$105 in the first month and $350–$530 in 6 months (depending on block difficulty).

As the price of Ether increased to $44.18 on April 4, 2017, the earnings from the “Ex07-1150-Rev01” would be ~$366 in the first month, with a network hash rate of 17,184 GH/s and a difficulty of 243.4162 trillion. As the cost of electricity (950 watts supply) would be $82.08 at $0.12 per kWh, the net profit from the system would be ~$284 in the first month. The predicted income in six months would be ~$750. However, this predication is very unreliable as the price is not stable and can change significantly.

As I said before, the calculation of earnings is dependent on the price of ETH and block difficulty. As of March 2017, the price of Ether broke past records and soared above $20, and on March 14, 2017, the price of Ether was $29.57 and the highest average difficulty, 180.235 TH, was recorded on 13 March. So according to the Ethereum profit calculator, the profit in the first month would have been $187, excluding the power costs. Despite the unbelievable increase in the Ether price, the earnings didn’t increase proportionately because more miners went online and the earned Ethers were divided among the increased number of miners.

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