[Beowulf]Infrastruture planning for small HPC 40/100 gigabyet eyhernet or Infiniband?

David Mathog mathog at caltech.edu
Mon Jul 28 12:41:23 PDT 2008

Jim Lux <james.p.lux at jpl.nasa.gov> wrote

> Quoting "Robert G. Brown" <rgb at phy.duke.edu>, on Mon 28 Jul 2008  
> 06:15:44 AM PDT:
> > On Mon, 28 Jul 2008, Eugen Leitl wrote:
> >
> >> On Sun, Jul 27, 2008 at 07:19:56PM -0700, Jim Lux wrote:
> >>
> >>> bear in mind that ordinary ethernet both coax and twisted pair is
> >>> galvanically isolated.
> >>
> >> This is strange, because I've seen (small) sparks and received (mild)
> >> shocks from both, in two different locations.
> >
> > Ground loop.  Very dangerous.  You go first...;-)
> >
> >    rgb
> Very odd.. I'd be looking for an outright short from the cables to  
> something (or, a LOT of capacitive coupling)...

Could this possibly be static electricity discharging?  Is the humidity
very low where this is being seen, and or, is the operator moving over
carpet shortly before the spark is observed?

I can't say that I've ever seen sparks leave an ethernet cable even here
in Pasadena when the winter humidity is close to zero, but I have had
sparks jump off my fingers as they passed near mounting screws on wall
plates.  In spark season I routinely get blasted by my car's door
handle, and there's definitely no ground loop going on there.

David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech

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