<div dir="ltr"><div><div>Dear rsync devs,<br><br></div>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:<br><br> $ dd if=/dev/urandom bs=1M count=50 of=sample.data<br> 50+0 records in<br> 50+0 records out<br> 52428800 bytes (52 MB, 50 MiB) copied, 0.24135 s, 217 MB/s<br> <br> $ rsync -avz --progress ./sample.data root@192.168.1.150:/dev/shm/<br> sending incremental file list<br> sample.data<br> 52,428,800 100% 575.23kB/s 0:01:28 (xfr#1, to-chk=0/1)<br> <br> sent 52,458,757 bytes received 35 bytes 543,614.42 bytes/sec<br> total size is 52,428,800 speedup is 1.00<br> <br> $ ssh <a href="mailto:root@192.168.1.150" target="_blank">root@192.168.1.150</a> 'rm /dev/shm/sample.data'<br> <br> $ rsync -avz --progress -e 'ssh -o "ProxyCommand nc %h %p"' ./sample.data root@192.168.1.150:/dev/shm/<br> sending incremental file list<br> sample.data<br> 52,428,800 100% 3.40MB/s 0:00:14 (xfr#1, to-chk=0/1)<br> <br> sent 52,458,757 bytes received 35 bytes 2,690,194.46 bytes/sec<br> total size is 52,428,800 speedup is 1.00<br> <br></div><div>If it isn't clear - the speed of the upload went from 543 kbytes/sec to 2690 kbytes/sec.<br></div><div><br></div><div>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).<br><br></div><div>Hope this helps people that backup over slow links (wi-fi or otherwise).<br><br></div><div>Cheers,<br></div><div>Thanassis Tsiodras, Dr.-Ing.</div>
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