[Beowulf] Southampton engineers a Raspberry Pi Supercomputer

Vincent Diepeveen diep at xs4all.nl
Wed Sep 12 08:42:01 PDT 2012

On Sep 12, 2012, at 5:24 PM, Lux, Jim (337C) wrote:

> Harkening back to earlier "make a beowulf of X".. one can hold a  
> Furby in one's hand.
> But anyway, this is kind of cool. It also shows some of the  
> practical problems of scalability: cable management, for one.  Look  
> at that picture of the 64 wall warts plugged into a bunch of plug  
> strips.
> Here's an interesting question.. I agree with the thought that this  
> kind of thing is useful for learning about using a cluster computer  
> (as opposed to parallel programming), and in a way that isn't  
> provided by emulation or multiple VMs or multiple cores running on  
> one box.  The physical cable management is one aspect.  The  
> complexity of moving software onto all nodes.. A blithe statement  
> of " rinse and repeat for each additional node" should fill most  
> people with terror, but doesn't, until you've had to do it.  Just  
> pulling a SD card out, shoving it in, running some windows utility,  
> etc. is a non-trivial amount of work.
> So, the question is...   what's the smallest number of nodes in a  
> "demo/toy" cluster that gives you the "big iron" feeling.  I'm  
> going to guess that 4 is too few.

Of course i should give now the answer 42.

Yet let's not do that.

I also stumbled with that question a year ago and the answer to it  
was 8-16.

And not raspberry pi's of course. Just normal PC's with a low latency  

As that requires problems with kernels, distro's and all those things  
a raspberry pi type cluster won't give.

You want to solve the cluster low latency WITHOUT buying a $2k  
license of RHEL nor SLES.
You want LATEST COMPILER, to get the MAXIMUM performance out of it.

Not a ready bought thing from intel.

You want latest GCC as it's way faster 64 bits and 32 bits at intel  
CPU's than oldie GCC 4.4 that's still in all those

OpenFabrics default doesnt work with GCC 4.7, you have to modify the  
scripts to do it.

With those raspberry pi's and such toy stuff type hardware you still  
don't feel the power usage, air refreshment need
of a cluster.

With a cluster that's around a 1.5 - 2 kilowatt you do. Maybe 3  
kilowatt is even better.

8 nodes here is 1.5 kilowatt, tesla's not counted.

You can't run 2 kilowatt in a small room without good ventilation and  
a normal airco won't do.
The airco i got here stops every week as then it's bag of water has  
been filled and it quits functioning :)

When it's humid outside, i can't even turn on airco as that just  
pumps water inside the water compartment of airco :)

It's filled within a few minutes then.

Of this entire area this is the only office with an airco of course.  
This much up north (Netherlands) you simply don't need an airco.
It's never real hot here.

So having one already is NOT COMMON.

There is a few chinese solutions there i saw on ebay, that i can get  
from hongkong, they're like 80 decibel or so. Not acceptable noise

Those noise levels you don't have with the cheapskate low power junk.

So what you might be used to there working with airco's; actually i  
asked the plumber to fix the airco a while ago.
He didn't know what to do you know.

So we did do it together.

No one knows about airco here.

The ones you CAN buy they would stop functioning in middle of night.  
If your few kilowatt cluster heats up the room then...

The biggest misconception is always that everyone has enough space to  
have a separated server room far away from where you do your job.
That's true for bigger companies, the small ones like me, they have  
the cluster next to them.

If you have the cash for that, you sure have the cash for a sysadmin  
as well.

The NOISE LEVEL is the problem here. It has to be quiet the cluster!

All those raspberry pi's and similar type junk won't give you that  

But most important: working with junk slow old hardware is not  
interesting to students. They want to be FASTER than their home PC.
So give them a cluster where the software running on it is FASTER  
than their home PC.

That's your  first priority, or they wll be all total desinterested.

>   64 is clearly enough..   Most cheap non-rack mount, non-surplus  
> ethernet hub/switches have 5-8 ports.  Maybe you need to have more  
> than 8 nodes to really get into the "how do I interconnect N things  
> when my interconnection device has only M ports", although you  
> could trivially contrive such a thing (use only 4 ports on a 8 port  
> switch)
> I've done 4 nodes a bunch of times, and that seems a bit too  
> trivial.  Heck, there's a lot of people who have 4 computers in  
> their office, forming a defacto heterogenous cluster.
> There's also that "as soon as we were able to source sufficient..."  
> statement...
> And I *still* think that a cluster of arduinos would be fun, albeit  
> slow.  Is there a (limited) MPI implementation?  There's some  
> interesting I/O devices for arduino that might be intriguing in  
> this context.. the 8x8 multicolor LED displays for instance.
> Jim Lux
> -----Original Message-----
> From: beowulf-bounces at beowulf.org [mailto:beowulf- 
> bounces at beowulf.org] On Behalf Of Eugen Leitl
> Sent: Wednesday, September 12, 2012 6:55 AM
> To: Beowulf at beowulf.org
> Subject: [Beowulf] Southampton engineers a Raspberry Pi Supercomputer
> http://www.southampton.ac.uk/mediacentre/features/ 
> raspberry_pi_supercomputer.shtml
> Southampton engineers a Raspberry Pi Supercomputer
> Professor Cox comments: “As soon as we were able to source  
> sufficient Raspberry Pi computers.”
> runs off a single 13 Amp mains socket
> “The team wants to see this low-cost system as a starting point to  
> inspire and enable students to apply high-performance computing and  
> data handling to tackle complex engineering and scientific  
> challenges as part of our on-going outreach activities.”
> James Cox says: “The Raspberry Pi is great fun and it is amazing  
> that I can hold it in my hand and write computer programs or play  
> games on it.”
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