[GTALUG] Wget under-reports data transfer rate ("bandwidth") by 5% (MB != MiB)

Peter Renzland renzland at gmail.com
Wed Mar 23 16:54:48 UTC 2016


> On Mar 23, 2016, at 10:23, Lennart Sorensen <lsorense at csclub.uwaterloo.ca> wrote:
> 
> On Tue, Mar 22, 2016 at 08:07:12PM -0400, Peter Renzland wrote:
>> Wget can be used to measure download data rate.
>> For example, 
>> wget --output-document=/dev/null http://speedtest.wdc01.softlayer.com/downloads/test500.zip
>> 
>> Then observe the progress meter and kill the process.
>> 
>> IMHO, wget thinks a MB is 2^20 (== 1MiB), instead of 10^6.  This results in a 5% error.
>> (Softlayer seems to have made the same error.)
> 
> It used to juse say K/s or M/s and they didn't want to change it to KB
> and MB to avoid wasting characters on the line for the progress bar.
> I guess someone eventually did change it, but did not want to change it
> to KiB and MiB.
> 
> If you use --report-speed=bits you get Mb/s and Kb/s and I think those
> are actually "correct".
> 
> Pretty sure wget predates the existance of KiB and MiB anyhow and changing
> the meaning later could "break" things.  Probably wouldn't though.

I've confirmed that --report-speed=bits gives the correct rate.

Also, Curl, with -w '%{speed_download}' gives the correct rate.

-- Peter Renzland at gmail.com







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