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

[Gerry Creager]

Back when the Earth was young, and the crust was still cooling, we ran 
serial connections between computers, over long distances and sometimes 
between power distributions.  It wasn't uncommon to see ground loops 
lead to arcing.  I don't see it as much now because I'm a little more 
careful about my grounds, and I bridge such problems with glass rather 
than copper.

The potential is still very real.

gerry

David Mathog wrote:
> 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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-- 
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
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