> You can simply replace the failed drive (there is no need to remove it
> first). 

When you say `replace' I am not sure whether you mean, `physically
replace', or `raidctl -F'.

The system can only accommodate two physical disks.  So I have to
remove the dead disk first, and I'd rather the system were powered off
when I did that. :-)

So I guess another way to put my question is: if I power off,
physically replace the failed disk, and restart, how will Raidframe
react to this?

I *think* what you are saying is that, whereas now I have:

  wd0d: failed
  wd1d: optimal

after restarting the machine I will have:

  component1: failed
  wd1d: optimal

and, therefore, I will be able to introduce (the new) wd0d into the
RAID without any complications.

Have I understood you correctly?