hopefully simple query regarding dd

[tech-lists]

Hello questions@

I couldn't find an an answer to this hopefully non-silly question and
can't test it meself without possibly risking a hd. Basically what I
want to know is this. Can I do this:

dd if=/dev/ada0 of=/dev/ada0

to refresh the disk, and *expect the outcome to be non-destructive for
the disk*. That bit is important. By non-destructive, I mean for the
data already on it.

Can I do this multiuser or do I need to boot to a rescue environment
beforehand?

thanks,
-- 
J.