Raspberry Pi server clusters

Hello!

I've been interested in building a cluster of computers ever since I read "How to Build a Beowulf" many years ago, but had neither time nor resources to do so until now.

The thinking in that book was that as Personal Computers became more powerful, so less powerful ones should drop in price. However, that didn't happen - they just disappeared from the market. So unless you

were lucky to find an organisation that was about to dump dozens of PCs, it was difficult to collect enough machines to get started. And then there were considerations about maintainability, power consumption

and waste heat removal...

However, now that Raspberry Pi's are readily available from Farnell and others, I've built myself a 4-node Beowulf, following on from the starting instructions given by Professor Cox of Southampton University

( http://www.southampton.ac.uk/~sjc/raspberrypi/ ). I'm now able to compile and run sample programs in C and Fortran, using MPI, and have started to write my own programs.

I aware of the reasons for a RPi Beowulf never being able to be a true "supercomputer", but my objectives at the moment are simply to learn about parallel processing, so performance is not a key issue for me at the moment.

I plan to add an Rpi node at the rate of one or two a month as my budget permits. Soon I'll have to address the hardware engineering issues as my litle Beowulf simply lives in a plastic Tesco storage box at the moment!

I've shared my learning so far on the raspberrypi.org forum at

http://www.raspberrypi.org/phpBB3/viewtopic.php?f=41&t=548 , but interest there seems to have died out.

I hope it's not going to do the same here, although the discussion about clusters seems to have moved away lately from RPi's to more exotic architectures.

Alan.   

Hi Alan!  Welcome to Element 14.

It was great to read your experiences with setting up a small cluster of Pi boards.  I read your posts on the RPF forum too, detailing your voyage of discovery.  Your writeup will probably be quite helpful to other people who want to follow the same path.

Although the Pi is clearly the wrong board to use if one's goal is HPC (even Eben Upton said as much), as long as "This is not for HPC" is clearly implanted in one's skull then the low price of Pi certainly makes cheap experimentation with clusters viable on a shoestring.  What's more, since nodes run headless and connected only by their Ethernet ports, this is an application that can probably run unaffected by the Pi's USB hardware problems.

I have to take issue with the dear Prof calling his project "Steps to make a Raspberry Pi Supercomputer".  It's not a supercomputer and never can be, it's simply a cluster.  Profs should not lower themselves to riding on hype bandwagons and claiming something which they know full well to be untrue.

Using such a cluster for non-HPC applications should certainly be interesting though, as we discussed at some length earlier in this thread.  A high availability web server would be one such application, focussing not on performance but on resilience.  The front ends would be easy to set up because they don't need to communicate with each other when serving web pages, but clustering your back-end database would certainly be interesting, and even challenging to do well.

It should be mentioned that while Pi is not directly useful for HPC, the picture starts to change when more modern ARM SoCs are considered.  In particular, the newly released Freescale i.MX6 SoC such as used on the Wandboard provides not only the extra power of Cortex-A9 cores but also on-SoC gigabit Ethernet and apparently OpenCL as well, so it certainly seems to be a candidate for modest HPC applications.

I look forward to reading more as your project progresses, especially if you add High Availability features.  It's worth pointing out that much of this material is relevant whichever ARM boards are used in a cluster.

Keep up the good work!

Morgaine.

The Raspberry pi is quite good for high performance computing, but we need someone with a lot of time on his hands and some technical talent to get mad at the VideoCore graphical processor. We have a whole bunch of "sample code" out in the open. Once someone reverse engineers that and writes an assembler/compiler, we'll be able to do gigaflops on the raspberry pi.

@coder27: network booting unavailable? I was just thinking about this  yesterday. It should be easy/possible to make a  program that acts as an pxe boot rom. Store it as "kernel.img" on the SD card, and off you go! This one is easier. It's just that someone needs to have this "itch" to make him scratch it. I've been crashing my kernel like tens of times on monday. So I couldn't copy over the newer kernel.img to the running system. Out comes the SD card, into the reader, update kernel, and back to the pi.  But after ten or twenty iterations you find what crashes your kernel (it was the printk, NOT the actual code I added that crashed the kernel. So I was under the impression that it kept crashing even when I removed all the code that did something.... )

Hi Morgaine:

Thanks for the welcome and kind words!

Yes, the "dear Prof" got me started on my Beowulf, then left me high and dry after showing how to run a pre-compiled C program. The learning curve to getting my own programs to compile and run on a 2-node system was quite steep, but fun. He also failed to address (or tell us about) aspects such as program version control on multiple nodes and system management. For instance, it takes me about 20 minutes to create a cloned SD card on my netbook, so re-building a 64-node system using his method would take nearly three 8-hour days! (Personally, I think his announcement was just for publicity purposes. I mean, tiny computers, supercomputers, Lego and a six-year-old child presses lots of hot buttons in the press. I wonder if he will get his cluster to do anything useful.)

I'm still going to focus on scientific / mathematical programming for a while, since that's my main interest. However, I'll delve into High Availability systems at some point.

Regards,

Alan. 

>Once someone reverse engineers that and writes an assembler/compiler

There is a very early attempt here:

https://github.com/hermanhermitage/videocoreiv/wiki/VideoCore-IV-Programmers-Manual

>Once someone reverse engineers that and writes an assembler/compiler

There is a very early attempt here:

https://github.com/hermanhermitage/videocoreiv/wiki/VideoCore-IV-Programmers-Manual