From a (crazed jumbo frame fanatic) network engineer at US cluster computing facility after 5 years of jumbo frame research and 3 years jumbo frame enabled success...
The broad scope LFN "math" for jumbo frames with TCP like protocols is: MaxRate = MSS/RTT * 0.7/sqrt(p) where MSS is maximum segment size, RTT is the round trip time, and p is the probability of packet loss. (Mathis et.al 1997) Since RTT is usually not under your control the equation is optimised by increasing MSS or reducing packet loss. Quick notes: -We see a throughput increases of 2-5 times in the building with 9K jumbo frames on GigE and 10GbE links. (Massive data sets and image files) -The latest Linux (e.g. 2.6.18) has autotuned TCP, all you need to do is increase the net.core and net.ipv4 maximum buffer values to match the expected maximum RTT. (We use 16Mbytes) -The latest Linux also has the new draft ieee pathmtu. -You need to watch out for applications. For example ssh has an internal TCP window and on an LFN you want the psc.edu patch. -Although most network gear is now jumbo clean (i.e. 9000 bytes and above) there are a number of firewalls that aren't. Anyone willing to run bwctld/iperf that wants a remote throughput test point please drop me an email. (There are a number of public bwctl servers on Internet2 if you prefer a different or more distant site.) http://www.psc.edu/~mathis/MTU/ {details of most of the above on this link} http://e2epi.internet2.edu/bwctl/ http://www.psc.edu/~rapier/hpn-ssh/ Paul Hyder NOAA Earth System Research Laboratory, Global Systems Division, High Performance Computing Boulder, Colorado The NZNOG list?... Because, I spend as much time as possible in Twizel. And yes, I got the gray beard the slow way. Jonathan Woolley wrote:
Jumbo frames aside from the usefulness of bigger payload for mpls/tunnels etc add some value in an environment where there's some packet loss.
I would have thought it makes it worse, assuming a physical fault resulting in a constant bit error rate combined with larger packet size means higher probability that a packet is corrupted (as there are more bits in it). The resulting packet is discarded which is a bigger loss than discarding a smaller one.
For example in an environment with say a 1Gbps link where packet loss is .1% with 1500 byte MTU you get 28Mbps througput. With Jumboframes that leaps to approx 162Mbps.
Can I see the maths behind this? If you're talking about packet loss due to congestion and not using TCP then you're probably right
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