Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!mips!public!thad
From: thad@public.BTR.COM (Thaddeus P. Floryan)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: TCP Throughput over E-net
Message-ID: <3254@public.BTR.COM>
Date: 29 Jun 91 07:37:14 GMT
References: <167@edi386.UUCP>
Organization: BTR Public Access UNIX, Mountain View CA
Lines: 36

In article <167@edi386.UUCP> eddjp@edi386.UUCP ( Dewey Paciaffi ) writes:
>I have a question regarding TCP throughput on Ethernet, and what affects
>it on a local network. I have 3 systems, two Sparc2s and an RS6000. I'll
>call them A, B, and C :
>[...]
>Could the flow direction impact the throughput this greatly? I would 
>normally attribute this to hardware and/or TCP implementation differences,
>but two of the machines are identical, and they all transfer 500 KB or
>greater to at least one other machine in at least one direction.
>
>Of course, I'd like them all to transfer at 850 KB to all machines in all
>directions :-). Is there something I've missed or something I should look
>at in my set-up here ?
>[...]

Omigosh!  :-)  I'd be happy to consistently get 100KBytes/S between systems
on my networks.

One observation I'd like to share is that file fragmentation and location of
contiguous free blocks dramatically affects the point-to-point transfer stats.

Remember: the sending system has to READ the file(s) from disk and the receiver
has to slurp the net and WRITE to its disk(s).  The last time I checked, I
recall the transfer timing starts just-prior to opening the source file(s) and
terminates just-after closing the destination file(s).

I've noticed as much as a 4:1 variation between "identical" systems due solely
to disk fragmentation (per my tests).

Also, the use of "trailers" seems to have an impact; do an "ifconfig X" where
<X> might be "en0" (or whatever's appropriate for your system(s)) and see if
"NO TRAILERS" is displayed.  All docs I've seen indicate the use of "TRAILERS"
(which typically is not displayed by ifconfig) reduces the amount of memory-
shuffling.

Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]