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[ILUG] cluster

# [ILUG] cluster

Sean sean at binky.net
Thu Oct 7 00:58:07 IST 1999

Dave Airlie wrote:
>
> Well hopefully U.L. Computer Society will be taking a donation of a
> cluster of 30 (give or take some damage) machines, which was being used as
> a Beowulf and which the society will re-use for this purpose, I'm sure the
> person who works on setting them up here will have more information in the
> future,
>
> The main thing with beowulf is getting stuff to run on it, most standard
> computing problems (i.e. getting netscape to run faster :-P) is not
> directly applicable to it, whereas lots of Maths and Physics problems run
> great on it .. but computer ppl no little or nothing about these problems
> !!!

\begin{rant}
Yes, thats what I keep trying to tell people.  Some don't have a clue
what
a cluster means !  Even that a 'cluster' is different than a beowulf
cluster !!

Usually in unix terms a cluster os a bunch/group of machines which
_share_
processes.  Processes can be 'migrated' to different machines as
required.
So that the cluster acts as one large machine, though nothing
parallelisable
about it.

A beowulf cluster is one where parallel jobs should be run. I.E. where
a program/problem could be run as if it was 'split up' and
_distributed_
amound the machines which make up the _beowulf_ cluster.  This is more
apparent
when considering what to write the program in and what the problem is.

The program should (read has in most cases, sgi an exception, maybe)
be 'parallelisable'.
(hopefully the spelling is right).  take drawing a picture.  A picture
consists of
rows and columns of pixels.  Say a picture of size 640x480.  Then is
you have a _beowulf_
cluster of, say 10 machines, then you could split the drawing of the
picture between
the machines, giving machine one columns 1 to 64 to draw, machine two
to draw columns 65
to (64 + 64) = 128 and so on.  This would speed up the drawing to a
peak of ten times the
usual found using just one machine.

A _cluster_ in the first mentioned terms would just have on process
doing the work, perhaps
on the best machine in the cluster, but not as fast as the _beowulf_
cluster.

A drawing of a picture is simplistic here, not taking into account i/o
to a video buffer
or anything.

To this end, the programming of a _problem_  (be it drawing a picture,
cracking passwords,
solving the problems involved in weather patterns/predictions), the
problem _has_ to be written
in an API concerned with parallel clusters, such as beowulf machines.

Usually these API's (Application Programmable Interface) are either
PVM (Parallel Virtual Machine),
or the industry standard MPI (Message Passing Interface), (MPI2 is now
out for a while).

The learning process is a bit of work, but ok.  Even on a single
machine, one can test out beowulf
type programs (just by running multiple part of the parallel program
on the one machine).
As a slightly biased opinion, MPI is the one to consider, though PVM
is not dying by a long shot.
(there are benefits to both, not needed for this discussion).

Lastly, there are some machines (and compilers) that can use single
SMP machiines to preform and
out preform parallel (beowulf) machines.  SGI machines are an
example.  EG. the Met Office
use one for running the stuff that predict the weather for Ireland
(same thing is used thru out
europe).

( of course cracking Word 97 passwords is totally parallelizable :-) eh
> Caolan?)

Oh damn so, but how one does it is the key.  Cracking any
password/encryption is
parallelisable,  look at the RC5 challange for example.  Another
example
of a parallelisable problem is the setiathome stuff.

>
> Dave.
>
> On Wed, 6 Oct 1999, kilmartin mark wrote:
>
> > Just writing this message to find out has anybody else on the list built a
> > Beowulf cluster or is there much interest in it in this country.

Trinny have a lot of interest.  They and Queens have an IBM SP
machine.
Nice one too.  (if ever one gets to run anything on it)

\end{rant}

Sean.
.
\begin{ps}
non of this new fangled html stuff, \TeX, \LaTeX, yeah!
\end{ps}
.



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