What's best and easiest to check sync result ?

[Bart Silverstrim]

Paul Johnson wrote:

> Please note that rsync does not give a "speedup" with local copies.
> WHen it copies a file, it copies the whole file.  The selective
> copying of portions of files is only done on network transfers.

Okay, this might clear up some confusion for me.

I read before that I can use rsync to copy just differences between 
files from A to destination B.

But when I did it to copy files as backups from my hard disk to an 
external drive, it would copy the whole file; so if I have a 5 gig 
tarfile, it copies the 5 gig over.

I thought from the docs that if the 5 gig file was something that just 
had a portion altered, like a 10 meg chunk, that 10 meg would get copied 
over to the appropriate section of the destination 5 gig file. But no, 5 
gig gets copied because it had a difference.

You're saying that if my sync was to a *network* destination then the 
behavior I expected would occur?

Is there a way to force this locally, or am I misinterpreting how it works?