[Beowulf] using extend-reach IB?

Mark Hahn hahn at mcmaster.ca
Thu Oct 11 09:15:52 PDT 2007

>> are they shipping? I checked their website a couple weeks ago
>> and they were talking 1q08 availability.
> You must not have looked thoroughly enough ... ;-) ... and you tend to be
> very thorough, but it was after regular business hours.  Intel is selling
> them directly from there webstore and they offer a couple of other
> vendors.  That is where I got the pricing.

I think you mean this page


right?  to me, it looks like they're all still listed as 
"Out of stock: available January 2008" like this:


perhaps you found a page of other products?  or is their stock warning bogus?

>>> speeds out to100m. A 25m cable is going to run you about $300 (US). Power
>> similar to Gore's one (which is copper I think).
> Mmm ... their website specs them out only to 25m (with asterisk) and that
>is a cable with a .9cm diameter! I wonder what the bend radius is on that?
>Even their photo of the cable looks like a cobra ... ;-) ... might be OK if
>you only need one I guess.  Did not see the pricing, but if it is the same
>as Intel's fiber why buy the snake? The claimed power draw is lower than I
>expected though ... anyone actually tested/used this cable?

my machineroom currently has something like 3.6 tons of quadrics cables,
which are all about 1 cm dia.  I don't find that the bend radius is much 
of a concern - space certainly is, since getting 38 quadrics out of a rack
is hard enough, not to mention switch racks which have 256 cables.
I believe even the thickest IB is slimmer than quadrics, but yes, I'm hoping
for optical in the next genreation.

though in general, I think the cluster layout is actually more important
than worrying about the cable.  for instance, distributing leaf switches
among racks is probably a good idea, and if you do that, you almost 
certainly want to use copper for short/local interconnect.

> It is a larger system product for now, but as bandwidth demands go up on
>smaller systems it won't be the length limitations that kill copper, but
>weight, diameter, added power draw, BERs, and equalizing total links costs.

I'm skeptical of the proposition that bandwidth is changing that much -
reeks of the great inet bubble.  within a cluster, sure, there are some 
apps which do really want more bw.  (though the most common bw-user I hear
of is weather codes which seem to do all-to-all purely out of laziness.)
bw out of clusters is probably growing, but at modest rates - have you 
priced a full-on 1Gb ISP link, let alone 10Gb?

regards, mark hahn.

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