[CentOS] evaluating backup systems: rsync

[Nicolas Thierry-Mieg]

Reindl Harald wrote:
>
>
> Am 19.01.2013 15:46, schrieb Nicolas Thierry-Mieg:
>> M. Fioretti wrote:
>>> On Fri, Jan 18, 2013 08:07:40 AM -0500, SilverTip257 wrote:
>>>> if you really want to eliminate that data being transferred, I
>>>> suppose you could do the extra work and rename the directory at the
>>>> same time on the source and destination.  Not ideal in the least.
>>>
>>> Not ideal indeed, but I'll probably do it that way next time that some
>>> renaming like this happens on very large folders. I assume that after
>>> that, I'd also have to launch rsync with the options that says to not
>>> consider modification time.
>>
>> no I don't think you will, since the file modification times won't have
>> changed.
>
> and even if the did - who cares?
>
> * rsync does not transfer unchanged data ever
> * rsync will sync the times to them from the sources
> * so have nearly zero network traffic

Not true: if you change the modification time on a file, by default 
rsync will copy the whole file again.

See man rsync:
Rsync  finds  files that need to be transferred using a “quick check” 
algorithm (by default) that looks for files that have changed in size or 
in last-modified time.

and yes I've tested this before posting  ;-)

to avoid this you need to use --size-only .