Testing LFNs

Wed May 6 16:07:39 UTC 2009

> Date: Wed, 06 May 2009 11:10:45 -0400
> From: "Kaegler, Mike" <KaeglerM at tessco.com>
> 
> I have a new T3 thats 65msec long. I'd usually be using iperf to test new
> links, but at 65msec, even at the maximum window size, I can only get
> 6-8mbit through. No combination of options I've been able to find has gotten
> me more than 6mbit through this link. Should I just shotgun 9 copies of it?
> 
> Are there better ways to test these links? Can one verify this link with
> just a pair of 7200s and linux machines on either side? Or is this something
> one really needs "real" test hardware for? If 6mbit go through clean, is
> there a real chance 44 will not?

What is "maximum window size"? For T3 at 65 ms (is that one-way or RTT?)
you don't need a really big window. Sounds like the system may need
tuning. See http://fasterdata.es.net/ I use iperf at multiple Gigabit
speeds and it works on a tuned system.

You might want to use UDP for testing. It does not care about RTT, but
is less efficient to receive. At 45 Mbps, there should be no problems,
though. 

If all else fails, run 4 or 5 iperf jobs in parallel. (Use a different
port for each.)
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
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