How exactly does rsync work? Is it smart enough not to transfer anything if your files aren't different?

Question

Not much to add to the question. How does rsync filter which data it must transfer and which it can leave alone?

Answer 1

Directly from the man page (http://linux.die.net/man/1/rsync):

"Rsync finds files that need to be transferred using a "quick check" algorithm (by default) that looks for files that have changed in size or in last-modified time. Any changes in the other preserved attributes (as requested by options) are made on the destination file directly when the quick check indicates that the file's data does not need to be updated."