On 01/19/2013 10:28 AM, Nicolas Thierry-Mieg wrote: > Not true: if you change the modification time on a file, by default > rsync will copy the whole file again rsync uses an efficient algorithm to compare file contents and transfer only the differences. Reindl was correct. rsync will use very little bandwidth in this case. You can test this by rsyncing a large file from one system to another, "touch"ing the file, and then rsync again. rsync will take a little while to generate checksums of the data to determine what needs to be copied, but will not transfer the entire contents of the file. If you run rsync with the -v flag, it will report the saved bandwidth as its "speedup". IIRC, this is expressed as the ratio of the size of files which were detected as not matching based on the given criteria (mtime and size by default, but possibly by checksum if given -c) to the size of data that was actually transmitted.