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Subject: Re: [OMPI users] switch and NIC performance (was: very bad parallel scaling of vasp using openmpi)
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-09-23 10:38:44

On Sep 23, 2009, at 10:15 AM, Dave Love wrote:

>> So, how does one go about selecting a good switch? "The most
>> expensive
>> the better" is somewhat a unsatisfying option!
> Also it's apparently not always right

+1 on Dave's and Joe's comments.

For example, not all of Cisco's switches are suitable for "ultra" HPC
clusters. Cisco has some very expensive switches whose goals are very
definitely not the same as what ultra HPC clusters typically need.
They're great switches (ok, I'm a bit biased ;-) ), but they're not
what you would need for an ultra HPC cluster. Buying one of these
would be kind of like buying an F-350 truck instead of an F1 formula
race car; both are excellent at their respective tasks, but they're
very different tasks.

My point: a network switch != a network switch != a network switch.
Make sure you understand what workloads and tasks the network switch
was designed for; don't just rely on published spec numbers -- they
don't tell the full story. Both an F1 and an F-350 can go 100 mph --
but they get there in very different ways.

Jeff Squyres