[CentOS] Re: Torrent: reminder to use it folks!

Kenneth Porter shiva at sewingwitch.com
Tue Dec 18 22:05:39 UTC 2007


--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.)



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