NFS Services Administrator's Guide

Configuring and Administering NFS
NFS Client and Server Transport Connections
Chapter 258
NFS Client and Server Transport Connections
NFS runs over both UDP and TCP transport protocols. The default
transport protocol is TCP. Using the TCP protocol increases
dependability on wide-area networks. Packets are successfully delivered
more consistently. TCP provides congestion control and error recovery.
NFS over TCP works with NFS version 2 and version 3.
NFS Client Transport Connections
An NFS client has a maximum number of connections for each server. By
default the maximum number of connections is one. The total maximum
number of connections on the client is the number of NFS servers
multiplied by the maximum number of connections allowed for each
server.
For example, say the maximum number of connections allowed for
client1 is two, if the network environment allowed client1 access to five
servers, the total number of connections allowed for client1 is 10: two on
each server. An NFS client remains connected to the NFS server until
the client becomes inactive: idle or disconnected by the client. By default,
idle time is 5 minutes. This means that there is no outbound request for
more than 5 minutes.
Support of 32K Transfer
NFS supports 32K transfer sizes across both TCP and UDP transport.
By default, NFS transfers 8K sizes. To specify 32k transfer sizes, set the
mount option for read- and write- size to 32k.
mount -F nfs -o rsize=32768, w=32768
Specifying TCP or UDP Connections
Using the mount command from the client with no protocol specified, the
behavior will be first to perform the mount using TCP. If that fails, then
it will try to mount the file system using UDP.
You can tell NFS to establish ONLY a TCP connection using the
following command:
mount -o proto=tcp