full upload happening even though only a timestamp has changed

[jw schultz]

On Tue, Apr 22, 2003 at 12:36:02AM +0000, Tom Goulet wrote:
> > If the mtime indicates the file has changed it will do an
> > update.  That doesn't mean that any actual file data will be
> > transfered.
> 
> That's what I thought was supposed to happen, but that's not what's
> happening.  My testing transfer has finished now and I'll show the
> transcript here:
> tomg at nova:~/mylibrary$ rsync -rtlPvessh /extra/library teep:/extra/tomg
> building file list ...
> 46349 files to consider
> wrote 1358812 bytes  read 20 bytes  44551.87 bytes/sec
> total size is 5240249974  speedup is 3856.44
> tomg at nova:~/mylibrary$ touch /extra/library/software/Knopper,_Klaus/KNOPPIX_V3.2-2003-04-18-EN.iso
> tomg at nova:~/mylibrary$ rsync -rtlPvessh /extra/library teep:/extra/tomg
> building file list ...
> 46349 files to consider
> library/software/Knopper,_Klaus/KNOPPIX_V3.2-2003-04-18-EN.iso
>    729716736 100%    1.02MB/s    0:11:19
> wrote 731164664 bytes  read 36 bytes  1005037.39 bytes/sec
> total size is 5240249974  speedup is 7.17
> tomg at nova:~/mylibrary$
> 
> As you can see, the second use of Rsync wrote 729805852 more bytes than
> the first.

The first time it didn't update the iso file.

> > If all the blocksums match it will effectively do a local copy to the
> > temp file and then rename back.  If you want it to do a whole-file
> > checksum as part of decideing whether to update you will need to use
> > the -c option which overrides mtime.
> 
> I don't understand much of that.  Do I have to use the -c command line
> option whenever I do not want Rsync to rely solely on the modification
> time?  I'm pretty confused.  I'm certain I could use Rsync without that
> option to make sure the remote file was right without actually uploading
> file data, it's not like I wouldn't notice two days of upload time.

Normally rsync uses file size and mtime to decide whether to
skip a file.  Generating checksums is expensive so that is
not done unless updating the file.  If you use -c it will
generate a file checksum on each end to decide whether to
skip instead of comparing mtime.

There is a known problem with files of this size where block
checksums fail on the first pass.  When that happens there is
a message that would look something like "redoing
filename(1524)" in stdout.  It is possible you are
encountering this problem and -P is hiding it.  Try
redirecting stdout, don't use -P and perhaps add an extra
-v.


-- 
________________________________________________________________
	J.W. Schultz            Pegasystems Technologies
	email address:		jw at pegasys.ws

		Remember Cernan and Schmitt