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This sync is taking all day, literally. Syncing from a mac (with rsync 3.0.5, from http://www.bombich.com/mactips/rsync.html) to Ubuntu with everything current. Internet is fast, computers are fast and not under load.

But bandwidth is orders of magnitude under capacity.

Am I doing something wrong?

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2 Answers

up vote 2 down vote accepted

What version of Mac OS X?

It's possible that you're running afoul of Mac OS X's TCP Delayed Ack algorithm. In most situations it increases performance, but in some cases it can hinder it. I can't know for sure that this is the problem from what you've told us so far, but it's quick to test. Try this:

  1. Check what it's currently set to:

    sudo sysctl net.inet.tcp.delayed_ack

  2. Turn if off:

    sudo sysctl -w net.inet.tcp.delayed_ack=0

  3. Start a new sync.

If that alleviates the problem, you can set this permanently by creating a file /etc/sysctl.conf and adding the line net.inet.tcp.delayed_ack=0 to it.

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This trick got me up to 60+ kbps consistently. I don't really understand it, but that's not the important part today. Thanks! –  Full Decent Sep 16 '10 at 17:57
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Please clarify what you mean by "internet is fast". Remember that you are UPLOADING from one of these machines, and upload is always slower (at least in aDSL, wich most homes and many business have).

Also, is there any other traffic using the same network? Especially if the mac is on a network with servers or other machines that have network stuff going on.

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