NFS Services Administrator's Guide (B.11.31.05) September 2009

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 the reliability of NFS filesystems working across WANs and
ensures that the packets are successfully delivered. TCP provides congestion control and error
recovery. NFS over TCP and UDP works with NFS Version 2 and Version 3.
NOTE: TCP is the only transport protocol supported by NFS Version 4.
Supporting 1MB Transfer for TCP mounts
By default, NFS supports 32K transfer sizes across both TCP and UDP transports.
To enable support of 1MB transfers for TCP mounts, you must first modify the following tunables:
• nfs3_bsize (for NFS version 3)
This tunable controls the logical block size used by NFSv3 clients. The block size represents
the amount of data the client attempts to read from or write to the server during an I/O
operation.
• nfs4_bsize (for NFS version 4)
This tunable controls the logical block size used by NFSv4 clients. The block size represents
the amount of data the client attempts to read from or write to the server during an I/O
operation.
• nfs3_max_transfer_size (for NFS version 3)
This tunable specifies the maximum size of the data portion of NFSv3 READ, WRITE,
READDIR, and READDIRPLUS requests. This parameter controls both the maximum size
of the data that the server returns and the maximum size of the request the client generates.
• nfs4_max_transfer_size (for NFS version 4)
This tunable specifies the maximum size of the data portion of NFSv4 READ, WRITE,
READDIR, and READDIRPLUS requests. This parameter controls both the maximum size
of the data that the server returns and the maximum size of the request the client generates.
• nfs3_max_transfer_size_cots (for NFS version 3)
This tunable specifies the maximum size of the data portion of NFSv3 READ, WRITE,
READDIR, and READDIRPLUS requests. This parameter controls both the maximum size
of the data the server returns as well as the maximum size of the request the client generates
over a connection-oriented transport, such as TCP.
• nfs4_max_transfer_size_cots (for NFS version 4)
This tunable specifies the maximum size of the data portion of NFSv4 READ, WRITE,
READDIR, and READDIRPLUS requests. This parameter controls both the maximum size
of the data the server returns as well as the maximum size of the request the client generates
over a connection-oriented transport, such as TCP.
For information on the nfs3_bsize and nfs4_bsize tunables, see nfs3_bsize(1M) and
nfs4_bsize(1M).
After the tunables have been modified, set the mount option for read and write size to 1MB, as
follows:
mount -F nfs -o rsize=1048576, wsize=1048576
Changes to the NFS Server Daemon
The NFS server daemon (nfsd) handles client filesystem requests. By default, nfsd starts over
TCP and UDP for NFSv2 and NFSv3. If NFSv4 is enabled, the nfsd daemon is started to service
all TCP and UDP requests.
42 Configuring and Administering NFS Services