Networker

Re: [Networker] TCP tuning in Solaris 8?

2003-07-14 17:37:02
Subject: Re: [Networker] TCP tuning in Solaris 8?
From: Oscar Olsson <spam1 AT QBRANCH DOT SE>
To: NETWORKER AT LISTMAIL.TEMPLE DOT EDU
Date: Mon, 14 Jul 2003 23:36:52 +0200
On Mon, 14 Jul 2003, Ty Young wrote:

TY> I searched the archives and the Legato eKnowledgebase but found nothing,
TY> so I'm asking here (if it's in the archives and I missed it, sorry.)
TY>
TY> I've heard discussions in the past about tuning TCP parameters in Solaris
TY> 8 to improve performance when backing up to tape.  Can someone shed some
TY> light on this, such as what the parms are and where I can read up more on
TY> this sort of thing?

Its not specific to solaris or legato, but rather TCP-specific. In
general, OSes are configured by default with a small windowsize, compared
with the average network of today. The windowsize controls how much data
can be sent before an acknowledge must be received for that chunk of data.
In modern gigabit-ethernet based networks, if one single TCP-flow should
fill a gigabit connection, the latency in the network prevents the host to
see the acknowledge packet on that chunk before the window has been
exceeded and thus halts transmissions until the ACK has been received.
There are also some other parameters that one should look into.

Googling after something like "TCP tuning windowsize solaris" should
probably find you something useful. To me, these URLs look useful:
http://www.sean.de/Solaris/soltune.html
http://www.syskonnect.com/syskonnect/support/info/htm/lanline_e.pdf

I did this research myself a year or two back, and this is what I do in
one rc-script:

# Local commands to run at start-up
/usr/sbin/ndd -set /dev/tcp tcp_xmit_hiwat 140000
/usr/sbin/ndd -set /dev/tcp tcp_recv_hiwat 140000

Hope this helps a bit.

//Oscar

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