Keep one BIG file in sync

Tom Diehl tdiehl at
Fri Feb 22 14:55:40 EST 2002

On Thu, 21 Feb 2002, Joseph Annino wrote:

> But I thought rsync will always copy the complete file, not just the
> differences.  So the checksums are for the complete file, and if the
> complete file checksum doesn't match, the complete file is transferred.
> That isn't whats desired here, just the differences WITHIN a file.
> If my understanding is wrong and rsync does have the proper magic to copy
> just the differences within a file then rsync is even cooler than I thought.

That is the magic of rsync and why I can keep 80 gigs of data in sync over 
a realitively small dsl line. My first encounters with rsync allowed me to keep
200+ megs of data in syne over a dial up. 

If you want the gorey details of just how it works go here: and read his thesis. A lot of it is wayyyyyyyyy
over my head but I got the gist of it. This was the first time I really
understood just how cool rsync is.

FWIW one of the really neat tricks is to download iso images and find out 
that for what ever reason they are corrupt. rsync will happly fix them for 
you. Another thing I use it for is keeping our ftp site in sync. When 
a new Redhat distro comes out rather than dload the whole thing I just 
copy the last distro to the new tree and rsync just dloads the diffs.

Rsync tis a wonderful program. :-))))))))


......Tom		CLUELESSNESS: There Are No Stupid Questions, But
tdiehl at	There Are LOTS of Inquisitive Idiots. :-)

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