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Chapter 3 System Preparation
172 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
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 Default Write Size 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.
SubSection WriteSize = <value>
E.g. WriteSize = 1MB
Size to be used for each individual write request to the network
May be specified as a decimal number or “xMB” style notation
SubSection TcpNoDelay = 0 | 1
E.g. TcpNoDelay = 1
Indicates whether the TCP Delay option should be disabled (0)
or enabled (any other value)
Table 3-6 Network Options Stanza Fields