Using Tcp; Preserving Acls - Red Hat ENTERPRISE LINUX 4 System Administration Manual

21.2.3. Using TCP

The default transport protocol for NFSv4 is TCP; however, the Red Hat Enterprise Linux 4 kernel
includes support for NFS over UDP. To use NFS over UDP, include the -o udp option to mount
when mounting the NFS-exported file system on the client system.
There are three ways to configure an NFS file system export. On demand via the command line (client
side), automatically via the /etc/fstab file (client side), and automatically via autofs configuration
files, such as /etc/auto.master and /etc/auto.misc (server side with NIS).
For example, on demand via the command line (client side):
mount -o udp shadowman.example.com:/misc/export /misc/local
When the NFS mount is specified in /etc/fstab (client side):
server:/usr/local/pub
When the NFS mount is specified in an autofs configuration file for a NIS server, available for NIS
enabled workstations:
myproject -rw,soft,intr,rsize=8192,wsize=8192,udp penguin.example.net:/proj52
Since the default is TCP, if the -o udp option is not specified, the NFS-exported file system is
accessed via TCP.
The advantages of using TCP include the following:
• Improved connection durability, thus less NFS stale file handles messages.
• Performance gain on heavily loaded networks because TCP acknowledges every packet, unlike
UDP which only acknowledges completion.
• TCP has better congestion control than UDP (which has none). On a very congested network, UDP
packets are the first packets that are dropped. This means that if NFS is writing data (in 8K chunks)
all of that 8K must be retransmitted over UDP. Because of TCP's reliability, only parts of that 8K
data are transmitted at a time.
• Error detection. When a TCP connection breaks (due to the server being unavailable) the client
stops sending data and restarts the connection process once the server becomes available. With
UDP, since it's connection-less, the client continues to pound the network with data until the server
reestablishes a connection.
The main disadvantage is that there is a very small performance hit due to the overhead associated
with the TCP protocol.

21.2.4. Preserving ACLs

The Red Hat Enterprise Linux 4 kernel provides ACL support for the ext3 file system and ext3 file
systems mounted with the NFS or Samba protocols. Thus, if an ext3 file system has ACLs enabled for
it and is NFS exported, and if the NFS client can read ACLs, they are used by the NFS client as well.
/pub nfs rsize=8192,wsize=8192,timeo=14,intr,udp
Using TCP
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