[OpenAFS-devel] Bad AFS performance over wide area due to packet fragmentation problems

[Rainer Toebbicke]

It's not the first time that people at external sites complain about 
bad AFS performance from our servers.

Usually, it boils down to that every now and then one of the routers 
or firewalls in the external networking clouds starts to choke on IP 
packet fragmentation - when we repeat the tests with "-nojumbo" 
everything works like a charm. The problem is that every time its the 
users who detect this, it takes some time until the problem surfaces 
at the sysadmin level, and the networking guys swear that there wasn't 
a change since ages.

As '-nojumbo' has a measurable price on our own local network where 
fragmentation does not exhibit any problem we hesitate to run 
everything in that mode.

Ideally, RX would be adaptive and stop using jumbograms when they 
cause problems, but I understand that the algorithm to detect those 
reliably can be challenging.

How about a config file a la NetRestrict then that turns off 
jumbograms to external sites, or allows them to others?

Any brilliant ideas?

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Rainer Toebbicke
European Laboratory for Particle Physics(CERN) - Geneva, Switzerland
Phone: +41 22 767 8985       Fax: +41 22 767 7155