--On Tuesday, December 18, 2007 12:52 PM -0500 Tom Diehl <tdiehl at rogueind.com> wrote: > If you are really curious about all of this magic have a look here: > http://rsync.samba.org/how-rsync-works.html Ah, here's the critical verbiage, in the section titled "The Sender": > If a block checksum match is found it is considered a matching block and > any accumulated non-matching data will be sent to the receiver followed > by the offset and length in the receiver's file of the matching block and > the block checksum generator will be advanced to the next byte after the > matching block. > > Matching blocks can be identified in this way even if the blocks are > reordered or at different offsets. This process is the very heart of the > rsync algorithm. Because an ISO is actually an uncompressed filesystem and the files within it are going to be aligned on CD/DVD block boundaries, matching files from the 5.0 and 5.1 release will differ only in block-quantized offset, so there should be lots of common blocks. (This assumes that the ISO block size is some integral multiple of the rsync block size.)