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Date:	Mon, 19 Sep 2011 08:06:21 -0400
From:	Eliot Moss <moss AT cs DOT umass DOT edu>
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To:	cygwin AT cygwin DOT com
Subject:	Re: File download taking longer time with SFTP( CYGWIN server)
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On 9/19/2011 6:59 AM, suresh_gaddam wrote:
>
> Hi All,
> We have an java application (which resides in Linux ) connects to client’s
> windows server and download files from there. Recently we upgraded our mode
> of transfer from FTP to SFTP. They installed CYGWIN SFTP server in windows
> machine. With SFTP its taking much longer time to download the files
> compared to FTP.
> PFB details
> -	Total no of files = 1,22,000
> -	Total load size = 58 GB
> -	Time taken with SFTP( CYGWIN server) = 28 hrs
> -	Time taken with FTP = 4hrs
> We did multiple rounds of testing and its taking much longer time with SFTP
> ( incomparable to FTP).
>
> Does SFTP with CYGWIN server takes longer to download the files? Are there
> any performance issues with CYGWIN? Is there anything which can be done in
> code perspective to download files faster ? , I don’t think so because the
> same code with FTP mode downloaded files much faster.

I am not sure if this would explain it, but sftp is probably
using encryption. This makes the data "on the wire" appear
random. Random data are not as compressible. You might want
to try schemes that compress and then encrypt. rsync can do
that (with appropriate flags).

What kind of link are the data flowing over? This issue of
compressibility would be particularly noticeable on dialup
though your rate sounds a lot higher than that. Roughly,
sftp gets 2Gb/hour, about 35Mb/min (say), which is over
500Kb/sec, while ftp is getting 7 times as much. Typical
text and program data might well show that degree of
compression (already compressed data such as typical
images and videos would not).

Regards -- Eliot Moss

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