--On Tuesday, December 18, 2007 12:52 PM -0500 Tom Diehl tdiehl@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.)