copy parts of file: newbie question.

Martin Pool mbp at
Tue Sep 4 21:37:49 EST 2001

On  1 Sep 2001, pl <pl at> wrote:
> Hello Martin,
> I'm new to this. Can you confirm that where possible, rsync will copy over
> only the "changed" *parts* of a file in a synchronisation?

Yes, that's the main feature...

> Putting it in a more pratical way; say you had "zip" file A_prime on disk 1
> and "zip" file A on disk 2. File A_prime was slightly larger and slightly
> different from file A, and we were moving from disk 1 to disk 2. Would rsync
> really just copy over the part of A_prime that was needed to change file A
> into A_Prime ??

... however small changes in an uncompressed file tend to cause large
changes in the compressed file.  

If both files are local the delta-finding algorithm can't help so
much, though, because the system has to read both disks to find the
differences.  It's most useful when the source and destination are on
different machines.  The main reason to run rsync locally are to take
advantage of the recursive-copy and exclusion features.


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