Keep one BIG file in sync

Dave Dykstra dwd at
Sat Feb 23 02:03:13 EST 2002

Keep in mind that rsync always generates a complete copy of the file on the
receiver side, it doesn't actually modify the file; it takes chunks out of
the original file and combines them with the changed chunks sent from the
receiver to make a new file, and when it's all done it deletes the old
one and moves the new one into place.

- Dave Dykstra

On Thu, Feb 21, 2002 at 11:28:50PM -0500, Joseph Annino wrote:
> This is cool.  You can't really tell that this is what is going on from
> reading the man page.
> On 2/21/02 10:55 PM, "Tom Diehl" <tdiehl at> wrote:
> > 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. :-))))))))

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