does the incremental rsync algorithm save on storage?

[Matt McCutchen]

On 7/17/07, Noah Leaman <noah at mac.com> wrote:
> >From what I understand, the incremental rsync algorithm saves on network bandwidth, but does rsync then just merge that delta data to end up with the new version and full sized file on the destination filesystem?

Correct.

> I have these Microsoft Entourage databases files that modified often and can be a few gigs in size...  I want to back them up with rsync, but if the whole file is backed-up each time it takes a lot of space up (...multiplied by many users). I want to just store the initial file then only the deltas for each backup after that.
>
> So my concern is not so much for bandwidth conservation, but storage conservation.

I recommend using rdiff-backup ( http://www.nongnu.org/rdiff-backup/
).  It produces a destination containing a full copy of the most
recent version of each file and a chain of backward deltas.

If you really want the original file and forward deltas, I recommend
that you use rsync's batch mode.  Pull the files to the receiver with
--only-write-batch, which makes rsync write a batch file containing
forward deltas from the (original) destination files to the current
source files instead of actually updating the destination.  To
reconstruct a non-original version of a file, use --read-batch to
apply the appropriate batch file to a temporary copy of the original
files.  This approach produces independent, cumulative deltas from the
original files; I can't think of an easy way to produce a chain of
forward deltas.

Matt