[Beowulf] NFSv3 client hangs - tcp v/s udp.

Robert Millner rmillner at fiendly.org
Mon May 8 11:19:05 PDT 2006

Were there any console messages on your NFS server?

A problem I ran into last year on a 384 node cluster was that Linux has
a hard coded limit of 20 TCP connections per nfsd.  This is a bare
constant buried in the kernel server code.

The console message on the server was:
nfsd: too many open TCP sockets, consider increasing the number of nfsd

On any specific nfsd, connection #21 would cause connection #1 to drop.
The client from #1 would then make the new #21 causing someone else to

If I recall properly (and may not so check this yourself) any specific
mount resulted in a TCP connection.  Size the number of nfsd processes
to be around (nodes * mounts)/20.  I haven't really had problems with
UDP on a low latency, well behaved network.

Anyway, not sure if this is germane to your actual problem but its one
to be aware of.


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