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Date:      Thu, 22 Nov 2001 17:41:08 +0800
From:      francisv@dagupan.com
To:        ryan@sasknow.com
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   RE: Maximizing throughput
Message-ID:  <10F29E27A956D511B0940050DA8D86A9340BE9@apmail.dagupan.com>

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Thank you, Ryan, for the detailed response. Please see my comments below:

-----Original Message-----
From: Ryan Thompson [mailto:ryan@sasknow.com] 
Sent: Thursday, November 22, 2001 5:31 PM
To: francisv@dagupan.com
Cc: freebsd-questions@FreeBSD.ORG
Subject: Re: Maximizing throughput

francisv@dagupan.com wrote to freebsd-questions@FreeBSD.ORG:

> Hi,
> 
> I have an Intel Pro 100/S NIC on FreeBSD 4.4-STABLE --
> transferring huge (~650MB) files to another computer is only
> around 1.78Mbps. The machines are connected via a Cisco 3500XL
> switch at full-duplex, 100Mbps. Is there any other way to increase
> the throughput or is this the actual bandwidth limit?

1.78Mbps is pretty abysmal for a 100Mbps link. There are a lot of
factors which may be causing this. I'm guessing (correctly, I bet)
that it is NOT a configuration issue with FreeBSD, unless prior to
this, you were messing with network settings that you shouldn't have.
:-)

So, I don't have an answer for you, but I'll take you through some
troubleshooting that will probably get to the root of the problem
fairly quickly.

For rates that low, packets are almost certainly getting dropped.

My first wave of questions goes something like this, 
1. What application layer protocol is being used to transfer?

FAV> FTP

2. Does it run over TCP or UDP?

FAV> TCP

3. Are you using CAT5 cabling between both hosts and the switch?

FAV> Yes, we're using category 5 UTP cable on both hosts; less than 5 feet 
FAV> per host to the switch

4. How loaded are the machines? The switch?

FAV> Between 5-10 percent load

5. How did you calculate your "speed" statistic? Are you sure?

FAV> I don't know if the throughput display (after uploading) of the FTP 
FAV> client is in megabytes or megabits; I'm guessing it's in megabytes, not

FAV> megabits. From my MRTG graph, it used a maximum of 15.6 megabits --
FAV> is this the actual throughput limit?

6. Are there any routers between the two hosts?

FAV> No, there are no routers in between

Things to try:
Connect the machines directly with crossover cable, or connect them to
a hub. Run tcpdump on one of the machines (or another host on the same
segment) and look for any weirdness.

As for possible causes/remedies, it's hard to say at this point. Like
I said, one of your likely symptoms is dropped packets. This could
happen at just about any layer. Maybe your cabling is poor grade (or
there is too much EMI), causing Ethernet frames to get dropped. Maybe
one of the hosts (or the switch) is configured wrong. Maybe your
transfer application is broken. Maybe one of your network cards needs
to be replaced. Maybe one of your cables is defective.

So, as for increasing the bandwidth limit, you'll need to fix whatever
is slowing things down. :-)

Hope this helps,
- Ryan


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