Weird NFS problems

Skylar Thompson skylar at
Tue May 31 08:45:12 PDT 2005

Jon Dama wrote:

>Try switching to TCP NFS.
>a 100MBit interface cannot keep up with a 1GBit interface in a bridge
>configuration.  Therefore, in the long run, at full-bore you'd expect to
>drop 9 out of every 10 ethernet frames.
>MTU is 1500 therefore 1K works (it fits in one frame), 2K doesn't (your
>NFS transactions are split across frames, one of which will almost
>certainly be dropped, it's UDP so the loss of one frame invalidates the
>whole transaction).
>This is the same reason you can't use UDP with a block size greater than
>MTU to use NFS over your DSL or some such arrangement.
>Incidentially, this has nothing to do with FreeBSD.  So if using TCP
>mounts solves your problem, don't expect Solaris NFS to magically make the
>UDP case work...

The thing is that UDP NFS has been working for us for years. A big part 
of our work is performance analysis, so to change our network 
architecture will invalidate a large part of our data.

-- Skylar Thompson (skylar at

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