[PLUG] How fast is my network, really?

[Brent Jones]

Quoting Carlos Konstanski <ckonstanski at pippiandcarlos.com>:

> On Mon, 19 Nov 2007, Russell Senior wrote:
>
>> Date: 19 Nov 2007 12:44:29 -0800
>> From: Russell Senior <russell at personaltelco.net>
>> Reply-To: "General Linux/UNIX discussion and help;	civil and on-topic"
>>     <plug at lists.pdxlinux.org>
>> To: "General Linux/UNIX discussion and help;	civil and on-topic"
>>     <plug at lists.pdxlinux.org>
>> Subject: Re: [PLUG] How fast is my network, really?
>>
>>>>>>> "Aaron" == Aaron Burt <aaron at bavariati.org> writes:
>>
>> Aaron> On Sun, Nov 18, 2007 at 11:11:34PM -0800, John Jason Jordan
>> Aaron> wrote:
>>>> My laptop and my desktop are connected over ethernet, all
>>>> components of which are cat6, and each computer has gigabit lan
>>>> built in. Since Aaron helped me get my backup partition on the
>>>> desktop fixed at the Clinic today, this evening I decided it was
>>>> time to back up the laptop to the desktop. By my calculation it ran
>>>> at about 105 MB per minute.
>>
>> Aaron> 1GB = 125 MB = 119 MiB.  Speaking as someone who's just
>> Aaron> finished a 12-month contract testing network hardware at Intel,
>> Aaron> 105 MB per second would be really good.  I can't guess why
>> Aaron> you'd see 1/60th of that, unless you're actually running at
>> Aaron> 100Mbps, or even WiFi at 54 Mbps.
>>
>> I don't know anything about dar, and this might not be remotely true,
>> but if there is encryption going on, there might be CPU bottlenecks.
>> Run top (or equivalent) at both ends to see.
>>
>>
>> --
>> Russell Senior, Secretary
>> russell at personaltelco.net
>
> My money is (once again) on Russ.  Encryption or compression would do
> the trick.
>
> Carlos Konstanski


My money is on a combination of mismatched network speeds. If you have  
a dumb switch that does support mixed mode, or dumb drivers that dont  
scale back properly, you'll end up with massive send a receive errors  
causing so many retires that you see slow speeds as the end result.
Compression or encryption in my mind wouldn't cause this.
I routinely send compressed and encrypted backups over the network. I  
use Bzip level 9, with ccrypt, over FTP/TLS. The most backwards way,  
yes, but I'm paranoid  ;)
Factoring in all that, I still only see about 30% CPU usage, and  
maxing out a 100mbit link easily.

A program I recomend for real time bandwidth usage on a clean console  
window is Slurm.

http://www.wormulon.net/slurm

Very clean and useful program for quick and easy realtime bandwidth  
usage visualization. Combined with Top, vmstat, and gstat for you BSD  
folk, you can pinpoint any bottle neck.

Brent Jones
brent at servuhome.net



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