NFS Services Administrator's Guide (B1031-90072, March 2011)

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
40 Configuring and Administering NFS Services