> Now you put a 2nd drive onto to mirror the first and provide redudancy.

From past experience that doesn't necessarily help.

The system runs fine until there is a power cut.
When you try to bring the system back up you fid that several
of the disks in the system do not want to start [1].
RAID wont help, you need that tape backup (and hope that
is still readable).

	David

[1] IIRC the probelm was caused by them running fairly warm
and evaporating out the oil from the bearings.  When the
drive had cooled down the bearing was too tight for the
motor to spin it.  Some (very old) drives had the spindle
end protruding so it could be freed by hand, other will
free if you rotate the case back and forward in you hard.
But sometimes you are just out of luck.

-- 
David Laight: david@l8s.co.uk