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SubSection TcpNoDelay = <value>
Values: 0, 1
E.g. TcpNoDelay = 1
Optional parameter Indicates whether the TCP Delay option should be
disabled (0) or enabled (any other value)
SendSpace & RecvSpace Controls the size of the receive and send buffers for TCP/IP sockets.
Internally, HPSS servers and clients attempt to set these buffers sizes explicitly, but other utilities
may not. Typically, the RecvSpace and the SendSpace are equal; however, this is not mandated.
Setting either of these values in excess of the system maximum will result in a value <= the system
maximum. The maximum can be observed/changed on AIX using the “no” command and
observing/setting the sb_max parameter. There is no portable mechanism for determining the system
maximum. Consequently, the specified values may be reduced until an acceptable value is obtained.
This process involves a bit-shift operation (divide by 2.)
RFC1323 Controls whether large TCP window sizes are used. Usually turned on (1) for higher
throughput networks (e.g. SP/x switch, Gigabit Ethernet, etc.) and turned off (0) for lower throughput
networks (e.g. 10/100 Mb ethernet, FDDI, etc.) Large windows provide for increased performance
over some networks, but may have a negative performance impact on others. NOTE: currently the
ability to enable or disable RFC 1323 support in this manner is specific to AIX. (An equivalent
setting for Solaris is the tcp_wscale_always flag, set with the command “ndd /dev/tcp
tcp_wscale_always”.)
The WriteSize allows the size of the individual write requests to the TCP/IP connections to be
configured. The default behavior (if no entry in the file matches a connection or if zero is entered for
the value of this field) is that the size of the write request is the size of the data buffer. On some
networks (e.g. the SP/x switch), improved performance has been measured by using a smaller value
(e.g. 32KB) for the size of the individual writes to the network. If no entry is found that matches a
network connection or the value specified is zero, HPSS will query an environment variable,
HPSS_TCP_WRITESIZE, and use that value, if set and non-zero, for the write size.
The TcpNoDelay option determines whether HPSS will enable or disable the algorithm that tries to
improve performance from small network writes. This algorithm attempts to coalesce small writes to
a TCP/IP connection so they can be sent in a single packet by delaying physical writes to the
network. HPSS typically disables this algorithm so that delays are not experienced while sending
Mover Protocol and parallel data transfer headers. However, if this causes a performance degradation
on a specific network (e.g., causes smaller than optimal packet sizes for large transfers), this can be
disabled for data transfer connections.
Network Options Stanza Specific Rules:
• The first matching entry found in the file will be used to determine the network options used
for that connection.
• Multiple “Source Interface Name” SubStanzas may be included within the “Network Options”
Stanza. A “Default” Source Interface Name SubStanza may be specified.
• The Source Interface Name SubStanza may specify one or more names [ subject to the
HPSS.conf line character limit (including the “= {“.) ] NOTE: Do not include the quotes
when specifying Default.
• Destination IP Address must be specified in Decimal Dot Notation.
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 271