Pentium4 cluster with Myrinet

[uccatvm]

Hi all,

We are in the process of procuring a fairly large computer, and one
option we are looking at is a Beowulf-type Intel (or AMD) cluster of
around 50 nodes with Myrinet. For the types of applications we are
looking at, a single node Pentium 4 with RDRAM performs much better 
than a PIII, probably largely due to the better memory bandwidth.
One of the vendors tells us that the current generation of P4 or Xeon
processors are less optimised for I/O, and are therefore less suitable
for a massively parallel machine, and we are recommended to go for a
Pentium III cluster instead. Do members of this list know about
serious issues of this kind with P4s?

We have also heard horror stories about dual Pentium III machines, 
with up to 40% performance loss if the second CPU is also running a
calculation. Is this really so bad? I would expect Xeons to be less
prone to this effect, because the likely bottleneck is the memory
bandwidth. Is that so? Is there any advantage in using RDRAM or DDRAM
with a PIII?

How do Athlons with DDRAM compare (both on the I/O / communication issue
and general floating point performance)?

There are different groups involved, but one of the applications we
would like to run is NWChem, a quantum chemistry program. Computation
patterns are much like Gaussian, but the program is designed for
massively parallel computers, so it runs very efficiently in parallel
(given a fast interconnect). Like Gaussian, it is very memory demanding,
doing floating point calculations on large arrays, and also uses a fair
amount of (local) scratch disk I/O.

I would be grateful for any answers to the questions above.

See you,

Tanja
-- 
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     Tanja van Mourik                                                
     Royal Society University Research Fellow
     Chemistry Department 
     University College London    phone:    +44 (0)20-7679-4663      
     20 Gordon Street             e-mail:   work: T.vanMourik at ucl.ac.uk 
     London WC1H 0AJ, UK                    home: tanja at netcomuk.co.uk     

     http://www.chem.ucl.ac.uk/people/vanmourik/index.html
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