rsync "-I" vs. "-c"

[Wayne Davison]

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 change, what method does it use to determine difference?

With -I, rsync does no advance determination of sameness, it just
transfers all the files and lets the matching data make the transfer as
small as possible.  This is more expensive than -c if all the files are
the same (since the receiving side reads the file twice and writes it
once for each file), but could be slightly faster than -c if most of the
files have changes (since the -c option makes the receiving side read the
file thrice and write it once when it is different, but only reads the
file once if it is the same).

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

When date & size are used, rsync skips the file when the modify time and
the size is identical on the receiver and the sender for a given file.

..wayne..