Anybody ever noticed how scp has always been significantly slower than for example a traditional FTP transfer? Well, I was reading an article about TCP performance tuning and it was discussing playing with the TCP buffer size (with socket options) so as to gain better bandwidth optimization (if any body is interested in the details I can spend 5 minutes on a sequel email). The interesting piece that I found is that OpenSSH suite (of which scp is a member) uses "statically defined internal flow control buffers" that limit the TCP buffer from getting larger which results in underutilization of the bandwidth! The Pittsburgh super computing center have their own patched version to overcome this.
I just thought it was worth sharing as I have noticed this issue a couple of years back but just figured it out the trick!
Happy Hacking
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abulyomon
www.KiLLTHeUPLiNK.com
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