rsync backup size

[Rashkae]

Robert Holtzman wrote:
> 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.


The total size is of the source.  That's your 6GB (after you add file
system overhead and files in the excluded dirs)


> 
> 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?
> 

You said the target already contained a full backup.  You need to use
the --delete option to prune files from the existing backup that are no
longer on the source