It often takes rsync a long time to start transfers because of the time to build the file lists of a (big) sync in both ends of the connection. Usually it's not rsync's fault; most of it is spent waiting for the machine to return stat info. Version 3 avoids this delay by starting the transfers without waiting for the complete file lists. However this only happens in two cases: if version 3 runs in both ends (which is still rare) and no options such as delay-updates are used. And this is even rarer... The rsync client first asks for the server to send it the whole file list, and does nothing during this period; only after having the sender list it starts to build the local one. Why doesn't it build the local list while waiting for the server's??? That could speed big syncs significantly.