Re: inconsistent HTTP download speeds on a LAN

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.

.