How far can you push rsync?

[sfr at canb.auug.org.au]

> well rsync can be told to treat the fs as one single file, like do rsync
> /dev/hda2 or some such, and it will then work happilly with the entire image
> and only transfer differences and such.

I thought this once as well, but it won't work as rsync does not do
update in place.  i.e. (even if it would sync the contents of a block
device - which I don't think it will) it would create a temporary copy
of /dev/hda2 and when it was finuished it would rename it over the old one
and you would end up with one (presumably very large) file (not device)
called /dev/hda2 - probably not what you want :-)

Cheers,
Stephen