Why is my rsync so slow compared to pure cp or even scp?

Posted by nfm on Server Fault See other posts from Server Fault or by nfm
Published on 2010-05-28T19:38:30Z Indexed on 2010/05/28 19:42 UTC
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rsync

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speed

I'm transfering the files from Linux to Windows 7 via a mounted share (the share is mounted from Windows on Linux).. I'm copying lots of data (i.e. nearly a TB) from the old to the new machine within my LAN. I'm unfortunate enough already that I only have 100MBit. Naturally I blindly used rsync but already wondered after a day why it feels so slow. Enabling the progress meter showed my a transfer rate of about 2MBit/s .

So I took a reasonable big file (800MB) and tracked the transfer timing:

cp : 05:33
scp (*): 06:33
rsync : 21:51

_{*) scp via localhost to the same Linux machine directly onto the share; completely useless but provided a progress meter}

The tests were as simple as

(cp|scp|rsync) <source> <destination>

No special arguments except host/port for scp. I even tried the -W switch for rsync but cancelled after ten minutes. rsync is 3.0.3 running on Lenny. To be able to interrupt the copy process anytime and resume lead me to rsync, but now I think I seriously need to reconsider this requirement.

How's such a big difference possible?

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