nfs and dropped udp datagrams

[Robert Schulze]

I wonder how big kern.ipc.maxsockbuf shall be tuned on a busy 
NFS-Server. In the last time, I often see clients loosing connection to 
their mounted directories. Furthermore, I see increasing counts for
upd datagrams "dropped due to full socket buffers" in netstat -s -p udp.

The mbuf situation does not seem to be the reason for the lost 
connections, vmstat -z shows 0 failures in the mbuf section.

Are there any other tunables which could prevent loss of connection to 
the server? What is a reasonable value for maxsockbuf?

With kind regards,
Robert Schulze