rsync backup size

[Robert Holtzman]

I run rsync with the command:

sudo rsync -vaHz --exclude '/proc' --exclude '/sys' --exclude '/media' / 
/media/disk

to back up to a usb hard drive that already had a full backup on it.

According to the man page, rsync uses a "delta-transfer algorithm, which 
reduces the amount of data sent over the network by sending  only  the 
differences between the source files and the existing files in the 
destination." This appears to happen with no special command option. The 
summary at the end of the process is:

sent 134629383 bytes  received 30327 bytes  2225780.33 bytes/sec
total size is 5635940395  speedup is 41.85

The total size agrees with the output from "du -ach /". The questions
that arise are

1. Does the total size in the summary relate to the source or the 
target? If it's the target, it means there was no compression.

2. Running "du -ach /media/disk" showed ~8 Gb (the backup is the only 
thing on the disk). Running "du -ach /" (with the usb disk removed) 
showed ~6 Gb. Why is the backup larger than the system, especially 
since I invoked the z option and was careful to exclude /media?

-- 
Bob Holtzman
"If you think you're getting free lunch,
  check the price of the beer"