ethernet and switches, was Re: [rescue] Mozilla Firefox

Patrick Finnegan pat at
Thu Apr 22 21:49:07 CDT 2004

On Thursday 22 April 2004 21:13, Dave McGuire wrote:
> On Apr 22, 2004, at 10:07 PM, Patrick Finnegan wrote:
> > Still, I love the idea of circuit-switched networks, instead of
> > packet switched ones like ethernet.  Mmmm, low latency.
>    Yeah, it'd be great if the cell size were larger than 53 bytes.  A
> single keystroke in telnet, for example, results in something like a
> 72-byte backet (or somewhere around that range).  ATM just doesn't do
> TCP/IP very well at all.

Yes.  I'd agree with you on that point.

> > Anyways, unswitched FDDI, like unswitched ethernet, still doesn't
> > scale well.
>    Uhhhhh, where did you hear that?  Media utilization rates greater
> than 95% are commonplace on FDDI.  It was built to scale, and it
> does.

Media utilization rate isn't everything.  If you've got 100 hosts a FDDI 
ring, you've got a 1Mbit/sec average bandwith.  When you've got a 
cluster of 48 processors trying to chat with each other to run a 
multi-way job, that isn't good enough.  (This is for $work, not $home).

If you hooked it up to a DEC GigaSwitch, then it'd be pretty nice.

I'm *not* saying FDDI isn't useful for real work, just not at where I 
work.  In fact, it'd be wonderful for smaller groups of machines, or 
machines that aren't trying to push 100Mbit full duplex out their 
network line.

> > Compared to Myrinet, it doesn't suck, and compared to Quadrix,
> > seeing its price doesn't make you go blind.  Right now, IB is
> > faster than Myrinet (and cheaper).  Of course, the bandwith is
> > wasted unless you've got something with PCI-X slots, which rules
> > out all of the Rescuable computers I know about.
>    Can I get an InfiniBand switch for the same twenty bucks that
> bought me a Myrinet switch last fall? ;)

Again, $work, not $home.  I picked up a Myrinet switch for $2 (one that 
uses the older, DC37 connectors) about a year ago.  It's nothing to 
sneeze at (>1GBit/s), but their current products leave a lot to be 
desired, compared to what other people offer.

Myrinet, the company, has their head up their ass, and after asking them 
what they were planning on doing to compete with IB (whose data rate 
was 4x what Myrinet was offering), they said, "well, we are planning on 
doubling our rate in the future."  If they don't start playing catch-up 
now, they shouldn't last much longer... and if it wasn't for their 
large installed userbase, they'd be dead by now.

Ahh yes, and there's that scaling issue they seem to have with the 
number 128.  If anoyone around here has to deploy more than 128 
machines connected via Myrinet, watch out.  128 is the maximum number 
of nodes you can have on a Myrinet switch, and when you start to stress 
the connections between switches, the tend to break.  Myrinet is 
supposedly having trouble setting up their gear on a 1024 node cluster 
at NCSA because of this issue, and they've been working on it for a 

Of course, none of this really applies to the "rescue" part of this what 
this list is about, at least for another couple of years.  Even I don't 
have >128 machines at home, let alone that many machines running, or 
which could use Myrinet cards.  

However, their older products are pretty nice, and they did have the 
market cornered on high-performance interconnects for a while.  If I 
had more than one adapter for my switch, I'd be using it, as it's the 
fastest networking gear I've got. Not bad for what is (IIRC) 5+ year 
old networking hardware.  Really Not Bad.

> > <set mode=$home>
> > FDDI (and it's slower friend, Token Ring) are fun, but not useful
> > for $work_stuff.
>    Wrong.  Sorry, but dead wrong.

You've gotta remember what I do for $work.  High Performance Computing.  
FDDI (unswitched) isn't.  Switched fast ethernet isn't.  GbE is getting 
there, and IB is pretty much there (for now).  We need something that's 
capable to do full-speed any-to-any communications for groups of 16-48 
machines.  If FDDI was switched, and did Gbit speeds, then it would be 
useful.  Same thing with TR.

$home, $fun is much different.  FDDI/TR is useful and can do Real Work, 
they're just not useful for My Job. :)

Purdue University ITAP/RCS        ---
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