NFS Performance Tuning for HP-UX 11.0 and 11i Systems

nfs performance tuning for hp-ux 11.0 and 11i systems page 97

Notes:

Page 97July 22, 2002

nfs/udp

vs.

nfs/tcp

Protocol-Induced Overhead

• UDP

Ø Lightweight, Connectionless, Unreliable

• TCP

Ø Connection Oriented, Reliable Delivery of Data

Ø Connection Management (establishment & teardown)

Ø Sequence and Acknowledgement Generation

Ø Congestion Control, Window Scaling

Ø Timeout and Retransmission Management

UDP is commonly described as a connectionless or unreliable transport protocol. It

is a very lightweight protocol, which is designed to quickly and efficiently deliver IP

datagrams between systems. By contrast, TCP is a connection-oriented transport,

which maintains established connections between systems and guarantees reliable

delivery of data.

The reliability provided by TCP does not come without some overhead. There is

connection management overhead (i.e. connection establishment and teardown),

tracking of sequence and acknowledgement information, congestion control, error

recovery, etc. In LAN environments, where latency is low and retransmissions are

few, the overhead imposed by TCP can hurt overall NFS performance.

How much does the overhead of TCP affect NFS performance? As with most

performance related questions the answer is ‘It depends’. Many factors can

influence the behavior and performance of UDP and TCP in a given network. It is

therefore difficult to predict how much impact converting from UDP to TCP will have

in an existing NFS installation. Thorough testing with both protocols is highly

recommended.