Circumference, the Datacenter-in-a-Box

Building a miniaturised datacenter-in-a-box with Raspberry Pi

Alasdair Allan
4 min readMay 21, 2018

There is nothing new about cluster computing, the move away from shared memory computing towards distributed cluster computing started more than 30 years ago. There’s not even anything really new about desktop clusters, or building them out of single-board computers, like the Raspberry Pi.

However, sometimes you come across a project that takes an old idea and re-implements it so well that it just flat out deserves respect.

Which is where the Circumference, a “miniaturised datacenter-in-a-box” from Ground Electronics, now on Crowd Supply, comes in. Because that’s exactly what this project does.

The Circumference 100. (📷: Ground Electronics)

The Circumference comes in two configurations, a 32 compute node version called the C100, and a smaller single-stack eight compute node version called the C25. Based around the Raspberry Pi and UDOO x86 platforms, both of the configurations have custom electronics for power distribution, control instrumentation, and status.

The smaller Circumference 25 (left) alongside the Circumference 100 (right). (📷: Ground Electronics)

Both units display a lot of thought, and beautiful design, with the enclosure finished in midnight black acrylic and cherry veneer, with the larger C100 having hinged doors to provide access to the compute stacks.

“When designing Circumference we were driven not to create the lowest cost solution, but by form, function and quality. Firstly, Circumference had to be a highly convenient form factor which significantly improved on existing solutions, and it had to look great sitting on a desktop or in a lab — which meant no Ethernet and power etc. cable clutter.”

Hinged doors provide easy access to C100 compute nodes. (📷: Ground Electronics)

“Each Raspberry Pi compute node has its own dedicated switch-mode power supply and instrumentation channel. One remote serial console is provided per eight nodes. An UDOO x86 is employed as a front-end processor (FEP) and has software control of power, instrumentation and console routing. The FEP is also used to run an e.g. Kubernetes or MPI master configuration, and in addition may be used to provide network file system and boot services.”

The custom-designed backplane is at the secret sauce of the Circumference units. Supporting eight Raspberry Pi compute nodes, a C25 uses a single backplane while the larger C100 has four of the custom boards. The C100 also has a custom front panel board.

The backplane is powered by a Microchip ATmega1280, while the C100 front panel board was built around a Microchip ATmega328. The firmware for both boards was developed using the Arduino development environment, and out-of-the-box support for cluster control is provided by a daemon running on the front panel board, with command line utility and Python and MQTT API for integration and monitoring.

Both the C25 and C100 are supplied as a kit of parts, minus the needed Raspberry Pis, UDOO x86 board, storage, and power supply unit.

While not, yet, open sourced. Ground Electronics has promised that both the design and firmware files for the Circumference will be made open source when the units ship to backers.

“The hardware designs — both mechanical and PCB — are not open at present, but we plan to publish these under an open source licence when the hardware for the main pledge levels (as opposed to the Early Access tiers) ships. This is also the case for the firmware and software, although we’ll likely publish these a little sooner than the hardware designs.”

Circumference is a product of Ground Electronics, based in Halifax in the north of England, and they’re raising now on Crowd Supply. The smaller C25 costs $599 without a power supply, although if you’re quick you can pick up an “early bird” unit for $549, or splurge for an “early access” unit at $599. The larger C100 costs $2,599, with no early bird discount, or early access, tiers available. Both units come with free worldwide shipping, although UK/EU customers also have to factor in another 20% VAT on top of these prices unless they’re ordering as a VAT-registered business.

Early access units are expected to ship in November this year, while the rest of the units should ship in January of 2019.

If I hadn’t spent the time to build my own four-node cluster, and add a second compute stack, I freely admit I’d be ordering one of these boxes to sit on my desk right now. Because the difference between my home-built cluster and the Circumference is the difference between a generic off-the-shelf white-label laser cutter, and a Glowforge. It’s all in the design and build-quality.