Seems like the easiest thing to eliminate network hardware would be to
pull a slow machine and move it the the location of a fast one, using
the fast ones connection - right down to the cable. That would
positively eliminate everything but the machine itself. From there you'd
have to look at similarities between the slow computers.

Kurt

David Magda wrote:
> Hello,
>
> We have an Apache 2.0.52 server on RHEL ES4u4 (2.6.9-42.ELsmp) that is running
> a CGI application. As part of the application, attachments can be downloaded by
> users. The server is connect via GigE to a central switch, and various clients
> are connected via LAN to various switches, which then connect to the central
> switch.
>
> For some clients the attachments are downloaded at 50-100 KB/s, but for others
> they get 2+ MB/s. The slow clients are of different OSes (Linux, OS X, and
> Windows) and are all on different VLANs. The fast clients are also various
> OSes and VLANs (i.e., switches / routers don't seem to be a common element).
>
> I'm trying to figure what the fast clients have in common, and how they are
> different from the slow ones.
>
> I've done a few tcpdumps, and the only difference between fast and slow systems
> (using the same OS) is that TCP window size gets to 60 KB in ~0.02s for the
> fast clients, but takes up to 0.80-1.14 seconds for the slow ones. I'm thinking
> this has something to do with TCP ramp up algorithms, but can't seem to figure
> out the differences between the two.
>
> One of the slow machines is Fedora 8:
>
> Linux lnx-slowA 2.6.24.3-50.fc8 #1 SMP Thu Mar 20 13:39:08 EDT 2008
> x86_64 x86_64 x86_64 GNU/Linux
>
> Another is Fedora 6:
>
> Linux lnx-slowB 2.6.18-1.2798.fc6 #1 SMP Mon Oct 16 14:54:20 EDT 2006
> i686 i686 i386 GNU/Linux
>
> One of the fast machines is Fedora 7:
>
> Linux lnx-fast 2.6.23.15-80.fc7 #1 SMP Sun Feb 10 17:29:10 EST 2008
> i686 i686 i386 GNU/Linux
>
> Any ideas?
>
> Thanks for any info.
>