Beowulf Questions

Patrick Geoffray patrick at myri.com
Sat Jan 4 16:42:19 EST 2003


On Sat, 2003-01-04 at 14:20, Eugen Leitl wrote:
> On Sat, 4 Jan 2003, Mark Hahn wrote:
> 
> > there simply is no coming breakthrough that will make all networking
> > fast, low-latency, cheap, ubiquitous and low-power.  and grid
> > (in the grand sense) really does require *all* those properties.
> 
> I'm not quite sure. The only hard limit on latency is relativistic (in
> vacuum, 1 ns = 0.3 m; 10 ns = 3 m, 100 ns = 30 m; 1 us = 3 km; 10 us = 30
> km, 100 us = 300 km).

It's it 300 Km = 1 ms ?
In a fiber it's almost half of that.

> cut-through WAN transmission technology) almost purely photonically
> switched networks where routing latency is negligible in regards to
> relativistic latency.

With a routing latency of the order of 1 us for current GigE hardware,
it's already negligible in regards of relativistic latency on WAN or MAN
(> 300 m). On LAN, this is another story.

> This clearly can't compete with dedicated ultralocal interconnects like
> Myrinet & Co, but it indicates GBit based clusters need not to be located
> physically close.

With clusters becoming larger and larger, the local components may not
already be physically close. For example, you may need 2 or more floors,
or several machine rooms in different building on the same site
(University). There is a real need for that, and that's why the next
Myrinet switching blade proposes Long-Haul (100 Km and more) fiber
ports.
Now, even for GigE, the difference between the routing latency and the
relativistic latency starts to be too important for distance greater
than 100 Km. So you can aggregate several clusters in a Grid way, but it
would only be interesting for embarrassingly // code if the clusters are
scattered across the US of Europe for example.

My 2 coins.

Patric
-- 

Patrick Geoffray, Phd
Myricom, Inc.
http://www.myri.com

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