rsync backup size

[Owen Townend]

2009/2/18 Rashkae <ubuntu at tigershaunt.com>:
> 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.
[snip]

The man page may not be entirely unambiguous about this.  The
compression is only for the transmission itself, the data doesn't stay
compressed.
This is for when cpu time is less limited than bandwidth which is not
the case here as the transfer is internal. Rsync is smart enough to
realise this and so there was no compression done - it would only
waste cpu for no benefit.
If you're trying to have the backup compressed you'll need to use a
compression tool such as gzip or bzip2. Gzip for example has an
--rsyncable flag to help with rsync's delta algorithm.

cheers,
Owen.