Mounting a powered-down HDD renders system unusable

[Diomidis Spinellis]

Mike Harding wrote:
> On a 5.4-pre system as of the last few days, If I mount a spun down hard
> disk (one I am using only for backup):

This does not answer your question, but may help you solve the problem.
  Try detaching the disk after you are done using it, and attaching it
again before you mount it.  I use this procedure for my backup disk.  It
has the advantage of allowing me to physically isolate the disk from the
computer.  The disk lives on a detachable disk drawer-style cabinet; by
pulling the disk drawer out an inch I severe the electrical connections
between the disk and the computer.  The idea is that even if the
computer gets electrically fried by lightning, the disk will survive.

Thus, the procedure I use is:

atacontrol attach 0
mount /backup
# Perform backup
umount /backup
atacontrol detach 0

-- 
Diomidis Spinellis - http://www.spinellis.gr