Bitcoin Mining: Six Months Later
By Jim Connors 28 February 2018

About six months have passed since first setting up a personal Bitcoin mining rig.  As a follow up to that original post, I thought it make make sense to return to see what's transpired during this brief -- and tumultuous -- period, and to discuss adjustments made to the rig.

What's Changed in the Bitcoin Universe?
My Humble Bitcoin Mining Rig (version 2.0)
Configuration Changes
Return on Investment? Really?

What's Changed in the Bitcoin Universe?

In a word, a lot (actually that's two words, but who's counting). Here are just a few trends:

• Bitcoin price volatility shows no signs of slowing down even as its market cap grows dramatically.  After the price of Bitcoin had nearly qunitupled from September to December 2017, it has since lost half its value in the subsequent two months.
• Mining is taking place on an even more massive scale.  Take a look at this, and this. In Russia, scientists were arrested for using top secret nuclear supercomputer facilities to mine cryptocurrencies.
• The worldwide Bitcoin hash rate has tripled in the last six months, meaning the competition for mining Bitcoins is getting more and more intense. Here's a nice website with lots of charts visualizing the growth.
• My mining pool, slushpool, has increased its Bitcoin hash rate capacity by ten fold, meaning without any increase in hash rate capacity on my end, my take of slushpool's winnings would be 1/10th what it originally was.
• China is escalating its crackdown on cryptocurrency trading. As it and other countries consider regulating this industry, further uncertainties surrounding Bitcoin are sure to arise.

My Humble Bitcoin Mining Rig (version 2.0)

Here's what the new version of the rig looks like.  The original rig can be viewed here.  Following is a description of the modifications.

1. Raspberry Pi 3: Even with the new and improved hash rate this rig provides, the Raspberry Pi 3 still has more than enough horsepower to serve as the overall controller.  The big change to the controller involves the addition of the Xtronix Power over Ethernet (PoE) Adapter for the Raspberry Pi.  With PoE, it's now possible to remotely reset the power on this rig.  In the Configuration Changes section of this article, software modifications have been made which make this platform much more reliable.  Nonetheless, the ability to remotely hard reset the rig does come in handy occasionally.
2. GekkoScience 2-pac (BM 1348x2) USB Bitcoin Miners:  The number of USB ASIC miners has been doubled from 4 to 8.  Running at 225Mhz, this rig now averages about 200 Gh/s (200 Billion hashes per second).  The power consumption stands at about 100 Watts, roughly equivalent to an old school incandescent light bulb.
3. HooToo 60W 7-port powered USB hubs: To accommodate the additional USB ASIC miners, two USB hubs have been added.  All four USB ports on the Raspberry Pi 3 are now occupied.
4. Artic Breeze USB fans: An extra USB fan was added to assure all miners are cooled adequately.

Configuration Changes

After running without incident for weeks, the Raspberry Pi began occasionally locking up, rendering it unusable until a hard reset was performed.  A search yielded this thread, where it appears others were experiencing similar problems.  Related to kernel memory corruption, a two-fold solution was employed to minimize the downtime associated with this tricky problem:

1. Enable SLUB debugging in the Raspian kernel.  Although this requires the Linux kernel to consume more CPU cycles, a large number of these intermittent memory allocation errors will be caught.  In order to configure and enable SLUB debugging, as root add the following line to the /boot/cmdline.txt file: slub_debug=FPUZ and reboot.
2. Configure in a watchhdog daemon.  Many processors come equipped with a watchdog timer which simply counts down from some set value to zero.  In order to prevent it from reaching zero, the system must periodically reset the watchdog timer.  If the timer reaches zero, it is assumed the system has hung.  The watchdog daemon detects this condition and can be configured to reboot when this occurs, lessening the need for manual intervention.  This procedure is typically hardware, Operating System and version dependent.  One way to enable the watchdog reset feature for a Raspberry Pi 3 running Raspbian Jessie is to follow these instructions.

Return on Investment?  Really?

Even though the price of Bitcoin has risen by about 2½ times its September 2017 value and my mining rig has doubled in capacity, those substantial gains cannot offset the tremendous increase in worldwide mining capacity.  Taking this point-in-time analysis with a grain of salt, the average current daily yield in Bitcoins for my rig (as of 26-Feb-2018) is .00001677.  Multiplied by the current price ($10,158 US) results in a daily reward of $0.17 US a day.  That's two cents a day more than the original setup but with double the power requirements (100 Watts vs. 50 Watts), not to mention the capital costs of the additional equipment. So to repurpose the punchline from an old joke: "we're losing money on every transaction and making it up in volume".