CPU Mining is back! A complete how to guide and profit analysis for Verium mining on a farm of single board computers - Part 1

TLDR version

If you already have a PC with spare cores then you could do a lot worse that pointing it at Verium mining, it is possible to profitably build CPU mining rigs from single board computers, and everyone should sign up for the free Azure trial and get it mining!

Introduction

I've been with Vericoin[1] since the very beginning, through the Mintpal theft, thought the rollback (the right decision IMHO), through the usual trolling, through the Proof of Stake Time[2] innovation to give a fully decentralised coin and now into the beginning of the new era of Verium[3] with it's Proof of Work Time protocol and the soon to be released integration between the two coins. Vericoin as the currency and Verium as the commodity.

I was lucky enough to get in on Vericoin with a batch of newly purchased gridseed miners so was able to mine at a reasonable pace even with the skyrocketing difficulties scrypt coins had back then. I wanted to be prepared for Verium so I duly built a water-cooled Core i7 6700k based machine overclocked to 4.6GHz with 16GB of RAM and it has been mining at a good rate since launch (very early hours of the morning here in the UK, but worth it to get in on those initial easier blocks!).

From my gridseed days I had a few Raspberry Pi's kicking around that had been used as controllers. I was curious as to what rate these cheap little boards might be able to mine Verium at, so downloaded, compiled and set off mining. The hash rate was not that impressive but the £ per H/m (Verium mining is measured in hashes per minute because of its scrypt n factor - 10242) was pretty intriguing compared to the PC that I had custom built... So I searched the web for what appeared from the spec sheets to give the best number of cores, clocked the highest with the right amount of RAM and settled on a Raspberry Pi 3 and an Odroid XU4 for testing.

This is the first in a series of articles covering my investigation into the Pi 3 and XU4 single board computers to mine Verium. This one is an analysis of their profitability (that's first as that's the bit everyone wants to know about right!?!). The second is a detailed set of instructions (including tweaking the mining software to get the best out of these boards) that anyone should be able to follow to recreate the set-up for themselves. The third is how to get all this up and running on Docker containers for easier maintenance at scale, and hopefully Docker Swarm if I can get it running on these devices.

Vericoin (VRC) and Verium (VRM) Overview
This section gives a brief overview of Vericoin and Verium - more info can be found on the Vericoin website [http://www.vericoin.info/] including some cool new explanation videos that have been contributed by community members.

Overview
The coin has non-anonymous and active developers. There is also an active community over bitcointalk, the vericoin forums and rocket chat channel.
Vericoin and Verium pairing coming in near-term future update

• Verium has 10x lower supply that Vericoin, and is 10x most costly to
  send
• Verium will have auxiliary mining of VRC and bonus VRC rewards
• Speed up the Vericoin block time to ~20 seconds
• Further decentralises Vericoin
• In wallet swap from Verium to Vericoin

Active on multiple exchanges, including VRC/VRM pairing on Livecoin

Vericoin
Total supply - 27,798,100 (at time of writing)
Proof of Work Phase:

• No premine, no ICO
• 26,751,452.35 VRC mined
• Scrypt algorithm

Proof of Stake Time (PoST) Phase:

• PoST Invented by the developers of Vericoin[2]
• Fully decentralised
• Proof of Stake protocol, no checkpoints, no supernodes
• Protocol security against
  
  • Competitive forks
  • Age attacks
  • Coin attacks
• More active staking gives higher rewards
• Disinflation targeted variable interest
• Minimum stake time of 8 hours for interest, no maximum

Verium
Proof of Work Time Phase:

• Protocol invented by the developers
  
  • Variable block time depending on network hash rate
  • Rewards in VRM per minute mining between blocks
  • Reward halving per minute decrease in block time
• Scrypt² algorithm, Scrypt N with N of 1024 - 128MB memory required per thread
  
  • Memory hard mining - ASIC and GPU resistant
• Block 1: 564,705 VRM minted for ICO participants who purchased VRM using VRC
  
  • 50% of IOC used for stake endowment fund
    
    • Address: VFEndownxxnHea9mv59kZx8c7TysGbndYx
    • Coins will never be moved, just interest from staking used in-perpetuity for infrastructure costs
  • How to use remaining the 50% of the VRC from ICO was voted for my community[4]
    
    • -20% Development
    • -20% Marketing and Design
    • -10% Third party partnerships

Profit Analysis

First off a bit of a disclaimer - I'm basing this all on the prices of the hardware that I have bought and the hash rates I've got out of that hardware with the specific mining software I will link to in a latter article modified as per the instructions. The XU4's that I've had each have a bit of variation in hash rate that they can manage and I've taken the middle ground that I've observed in this analysis - I haven't recorded and taken any kind of scientific approach to finding the mean hash rate over all the miners over x days. Having said that I'm pretty confident that you can achieve equivalent results by following the same / similar steps just don't go buying huge amounts of hardware without satisfying yourself these results are correct!

I'm also going to be using £ as my unit of currency (being from the UK!) throughout but it's the ratios between the different options that count regardless of which currency is being worked in. However you might get a better price for buying hardware where you live in the world so I've also linked the spreadsheets used to do the calculations so you can enter your own figures for comparison.

System Specifications

For each section below I will be basing the comparisons the following systems:

• A top-end desktop PC running Windows 10 (Core i7 6700k at 4.6GHz with 16GB RAM) - referred to as "PC" from now on
• An Odroid XU4[5] running Ubuntu (Samsung Exynos5422 - four big cores (ARM Cortex-A15 at 2GHz) and four small cores (ARM Cortex-A7 at 1.4 GHz) with 2GB RAM) run headless - referred to as "XU4" from now on
• A Raspberry Pi 3 Model B[6] running Raspbian (ARMv8 quad core at 1.2GHz with 1GB RAM) run headless - referred to as "Pi3" from now on
• Windows Azure "Standard DS3 v2" hosted in Northern Europe running Ubuntu (2.4 GHz Intel Xeon E5-2673 v3 (Haswell) 4 cores, 14 GB memory) - referred to as "Azure" from now on

The mining software used for hash rate comparisons is VeriumMiner[7] which is a fork of CPUMultiMiner adjusted to show hashrates in the right formats. This miner appears to give similar hash rates between windows and linux systems. SSE extensions are checked for and used at runtime on the PC and Azure systems, and the ARM based boards had the NEON extensions enabled at compile time. For the ARM boards the miner source was adjusted to allow maximum threads with the limited memory - full details of how to do this in the second article. Running less threads with more memory allocation per thread produced significantly worse results so isn't covered here.

Table 1 below has the comparative hash rates achieved with these set-ups, as above these are middle ground observed hash rates. For comparison there is a list of computers and hash rates people have achieved for VRM mining on the Vericoin forums[8], my PC is comparable in terms of hash rate to equivalent machines in the list.

Table 1 - Hash Rate Comparison

System	Hashes per minute
PC	~2200
XU4	~380
Pi3	~110
Azure	~1390

Purchase Price vs H/m

The system descriptions below provide a comparison of the purchase price of the base hardware needed for each system to get it up and running as single units. Table 2 lists the additional hardware needed by the XU4s and Pi3s to get a working system that scales based on 10 miners. Scaling is important to take into account as, for example, netgear home routers (which is what mine is) have a limit of 32 clients per wifi channel[9] therefore going wifi with a larger number of these boards is probably impractical / needs more wifi routers so i have priced in fixed networking hardware. Other options are probably possible, but I leave those to the reader to figure out (and share if they are better!). I've also ignored mounting hardware, e.g. threaded bar / standoffs / nuts / baseplate / velcro / etc. in this comparison. I will include a full bill of materials, including links / stock codes in the second article. Table 3 brings all this together to give overall £ per H per min figure for each option. All prices are including UK VAT. Also for those in the UK don't forget Quidco (shameless referral link!), can get cash back on quite a few of the bits below!

PC System - £1478

Scan 3XS Overclocked Bundle Z170 OC20 (~£700)
Processor - Intel Core i7 6700K overclocked to 4.6GHz.
Motherboard - Asus ROG Maximus VIII Ranger
CPU Cooler - Corsair Hydro H100i v2 GTX
Memory - 16GB Corsair Vengeance 2666MHz DDR4
Hard disk - 2TB SEAGATE (~£60)
Solid State Disk - Samsung 840 EVO 250GB (~£80)
Operating System - Windows 10 Home (£~85)
Wifi Adaptor - Edimax EW-7822PIC PCIe AC1200 (~£31)
Case - Corsair Carbide 600Q Case (~£100)
Power Supply - Corsair AX1200i (~£300)
Graphics Card - MSI HD7950 (~£150)
(www.scan.co.uk - they take bitcoin :))

XU4 System - £81.63

Single board computer and power supply, (http://www.odroid.co.uk/, small discounts may be available buying in bulk but this is worst case number - I've been dealing with a very helpful and response guy called Clive. You can also buy direct from OEM http://www.hardkernel.com/ but exchange rate, taxes, import duties etc. don't make it worth it in the UK) - £78.04
8GB Micro SD card, 7 day shop - £2.79
Ethernet patch cable, Farnell - £0.80

Pi3 System - £38.78

Single board computer, no power supply, (https://www.amazon.co.uk/, cheapest price even when taking into account bulk discounts from Farnell/CPC and RS) - £28.99
Power Supply, Amazon - £7
8GB Micro SD card, 7 day shop - £2.79

Table 2 - additional hardware to run 10 XU4 or Pi3

Item	Supplier	Qty	Total Price
5v 40A power supply - LRS-200-5	Mouser Electronics	1	£32.04
16 port switch	TP Link (amazon)	1	£26.12
Power leads (DC Power connector / micro usb, cable)	Farnell	10	£9
Remove power supply for Pi3 - not needed as common power supply	N/A	-10	-£70

Table 3 - £ per H per minute

System	Price	Hashrate	£/H/m (rounded)
Single XU4	£81.63	380	£0.22
10 x XU4	£883.46	3800	£0.23
10 x Pi3	£384.96	1100	£0.35
Single Pi3	£38.78	110	£0.35
PC	£1478	2200	£0.67
Azure	N/A - no initial purchase price

Running Costs per day vs H/m

Table 4 contains the daily (24 hour) running costs for each system. This assumes an electricity price of £0.1/kWh. Power at the wall was measured with an Energenie Power Meter which claims +/- 2% accuracy. Consumption varies, and so these are again unscientific average figures taken by observation. The better/lower power figures for the 10x systems is probably a combination of higher efficiency power supplies and the meter accuracy. Having scaled the XU4 system up to 40 unit then can say that the power usage at 10 units roughly correlates and is probably a bit higher. The Azure price is based on hosting costs for 24hrs.

Table 4 - £ per day per H per minute

System	Power Usage (at the wall)	Price/day	Hashrate	£/day/H/m (rounded)
Single XU4	~18W	£0.0432	380	£0.000114
10 x XU4	~160W	£0.384	3800	£0.000101
10 x Pi3	~70W	£0.168	1100	£0.000168
Single Pi3	~7.5W	£0.018	110	£0.000164
PC	~124W	£0.298	2200	£0.000135
Azure	N/A	£3.30	1390	£0.00237

Profit Summary

Table 5 contains a summary of the profit that can be generated from each system in hours, days, months and years post electricity costs. These are all calculated with the following parameters (correct at the time of writing):

• VRM/BTC - 0.0004 BTC
• BTC/GBP - £492
• Network Hashrate - 970 kH/min
• Block Time - 4.51666667 min
• Reward - 5.72994331 VRM

The spreadsheet at [10] can be used to input different prices, hardware and network information to look at potential returns. The unique algorithm that Verium uses linking hashrate, block-time and reward means that mining should be profitable for longer than with other PoW coins.

From the table it can be seen that the Odroid XU4s are by far the most profitable option for CPU mining, and so the next article will focus on how to build a scalable miner based around Odroid XU4s controlled by a Raspberry Pi3. A picture of the completed miner can be seen below - making around 15kH/m and consuming around 600W.

Table 5 - Gross Profit Summary (after electricity costs)

System	Per Hour	Per Day	Per Month	Per Year
Single XU4	0.0041	0.0976	2.9293	35.6393
10 x XU4	0.0427	1.0244	30.7326	373.9128
10 x Pi3	0.0100	0.2397	7.1910	87.4905
Single Pi3	0.0009	0.0228	0.6831	8.3111
PC	0.0124	0.0216	0.5178	15.5340
Azure	-0.2535	-6.0848	-182.5445	-2220.9576

Return on Investment

With the current prices and VRM reward (as above) return on investment is in the order of 28 months. Clearly this is a long time, however price can go up and down a lot over this time period and comparing Verium to other coins with similar total supplies it does seem vastly undervalued currently.
It is likely that a technology re-fresh of the miner would be desirable at some point in this timescales to take advantage of the latest processors to maintain its compatibility. This is where hardware resale would come into play.
This one might be a bit of moot point for those that want to keep their computer after it's no longer profitable to mine with it / it's time to move on to the next project but for those people that have bought the hardware for the specific purpose of mining then re-sale will enter into the equation. All the hardware is easily resalable however it's hard to predict price and likely isn't anywhere close to being a deciding factor for which hardware is best (and so hasn't been included in the profit analysis) but can be viewed as a nice bonus!

Solo vs Pool Mining

As the hash rate on the network rises the rate at which those with smaller miners manage to hit blocks will drop as they have a smaller percentage of the overall network rate, however statistically the small miners will still hit their expected share of blocks over time.
The psychological advantage of pool mining is that small amounts of VRM will be earned more frequently, however with the VRM transmission fee structure it is relatively expensive to send from the pool back to the wallet. Pool fees also have to be taken into account over and above the transmission fees.
Taking both these into account in the long term it will be more profitable to solo mine, but then probability of hitting a block comes into account and this has to be balanced by the miner to match their risk / reward appetite. Realistically most people will rather take the hit on fees and pool mine as they like to see the rewards trickle in instead of waiting to hit that block. This is good news for the pool operators!

Summary

Takeaway from this is that if you already have a PC with spare cores then you could do a lot worse that pointing it at Verium mining, it is possible to profitably build CPU mining rigs from single board computers and everyone should sign up for the free Azure trial[11] and get it mining, but it's not worth paying for. There might be other options in terms of configurations on Azure but don't think it would be possible to find a profitable combination from the look that I have done.

References

1 - https://www.vericoinforums.com/, https://bitcointalk.org/index.php?topic=602041
2 - https://www.vericoinforums.com/threads/vericoins-post-white-paper.1002/
3 - https://bitcointalk.org/index.php?topic=1540023
4 - https://www.vericoinforums.com/threads/ico-poll-for-remaining-50.1327/
5 - http://www.hardkernel.com/main/products/prdt_info.php?g_code=G143452239825
6 - https://www.raspberrypi.org/products/raspberry-pi-3-model-b/
7 - https://github.com/effectsToCause/veriumMiner
8 - https://www.vericoinforums.com/threads/verium-hashrate-comparision.1392/
9 - http://kb.netgear.com/…/how-many-clients-can-you-connect-wirelessly-to-a-netgear-router
10 - https://goo.gl/VUavUn
11 - https://azure.microsoft.com/en-gb/free/