delta copies

[Robert Fitzpatrick]

I posted the other day about trying to determine why my backups seem not
to be doing this. I am trying to figure this out this weekend, I have
two files on a RAID0 FreeBSD file system using SATA drives. I do a
simple tar of /var twice and then rsync the two files only as a test, no
folders involved....trying to determine why the entire file is being
copied in its entirety and not synchronized bit-by-bit. Is it dependent
on file types that can be done this way. Stephen was helpful the other
day to reply and he is able to rsync sql backups, exchange, etc. I've
tried with uncompressed pgsql backups and now tar, neither
working...Does rsync require certain compile options perhaps that I am
missing?

esmtp# ls -la test*
test:
total 1268356
drwxr-xr-x   2 root  wheel         512 Sep 22 18:46 .
drwxr-xr-x  11 root  wheel         512 Sep 22 18:46 ..
-rw-r--r--   1 root  wheel  1298128896 Sep 22 18:47 testvar.tar

test2:
total 1268388
drwxr-xr-x   2 root  wheel         512 Sep 22 18:49 .
drwxr-xr-x  11 root  wheel         512 Sep 22 18:46 ..
-rw-r--r--   1 root  wheel  1298163200 Sep 22 18:49 testvar.tar
esmtp# rsync -az --progress --stats test/ test2/
building file list ... 
2 files to consider
./
testvar.tar
  1298128896 100%   13.00MB/s    0:01:35  (1, 100.0% of 2)

Number of files: 2
Number of files transferred: 1
Total file size: 1298128896 bytes
Total transferred file size: 1298128896 bytes
Literal data: 1298128896 bytes
Matched data: 0 bytes
File list size: 53
File list generation time: 0.001 seconds
File list transfer time: 0.000 seconds
Total bytes sent: 178178479
Total bytes received: 48

sent 178178479 bytes  received 48 bytes  1846409.61 bytes/sec
total size is 1298128896  speedup is 7.29

However, I have a Microsoft SQL Server (binary compressed) backup being
transferred between two Windows servers using cwRsync and this is
working fine. It only takes a couple of minutes compared to almost 30
minutes in the initial transfer. After setting that up for a customer is
when I realized this was possible after using rsync for years doing
backups on our own Unix servers. So, I'd like this to happen for me,
thanks for any help...Also, does the match data bytes show the amount
matched when making delta copies, I assume? This seems to be the case as
the above shows zero and I see almost the same amount of byes here in my
Windows transfer.

-- 
Robert