On Mon, 2 Apr 2018 15:05:14 +0200 Thanassis Tsiodras via rsync <rsync@lists.samba.org> wrote:
> I recently concluded a bug hunt to trace why my rsync-ing to an SBC > was much slower than the corresponding iperf3-reported speeds. To > give a concise summary of the situation, in slow wifi links using SSH > with ProxyCommand tremendously speeds up things: > $ rsync -avz --progress -e 'ssh -o "ProxyCommand nc %h %p"' > ./sample.data root@192.168.1.150:/dev/shm/ > If it isn't clear - the speed of the upload went from 543 kbytes/sec > to 2690 kbytes/sec. > > If you want to see why - and how I traced this down - you can read my > complete report in the UNIX StackExchange forum. To avoid being > classified as a spammer, I won't include a link - search for question > 434825 in the search bar. The executive summary is that SSH disables > Nagle's algorithm by default - and in slow links this can cause > tremendous impact (as you see above). > > Hope this helps people that backup over slow links (wi-fi or > otherwise). In the interest of collecting ssh-related issues in a single thread I add this note: The HPN patches to the portable OpenSSH implementation can improve speed over high speed links with long round trip times. https://www.psc.edu/hpn-ssh It also helps in those cases where CPU is a bottleneck and encryption of transmitted data unnecessary. The FAQ is also interesting. The executive summary is: SCP and the underlying SSH2 protocol implementation in OpenSSH is network performance limited by statically defined internal flow control buffers. Regards, Karl <k...@meme.com> Free Software: "You don't pay back, you pay forward." -- Robert A. Heinlein -- Please use reply-all for most replies to avoid omitting the mailing list. To unsubscribe or change options: https://lists.samba.org/mailman/listinfo/rsync Before posting, read: http://www.catb.org/~esr/faqs/smart-questions.html
