rsync "-I" vs. "-c"

[Chris Shoemaker]

On Sun, Aug 01, 2004 at 06:20:11PM -0700, Linda A. W. wrote:
> If I use the "-I" to ignore date and size as quick-check methods of 
> determining

just modtime.  rsync never ignores size differences.

> change, what method does it use to determine difference?  If it falls 
> back to
> checksumming the entire file, maybe the manpage might warn that this 
> would be
> as expensive as using the "-c" option...or not depending on what it uses for
> determining difference at that point.

Short answer:  It does fall back to checksum comparison.

Long answer:  I'm not sure, but I suspect that the reason this is not so
explicit in the man page is that it's a bit complicated in the code,
too.  I _think_ that using -I would be even more expensive than -c,
because it will take longer to eventually do the same checksum
comparison.

But, Wayne knows these options like the back of his hand.  Wayne?

-chris

> 
> So exactly how does rsync compare files for differences when date & size are
> used but checksumming is not?
> 
> Thanks!
> -Linda
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