[Bug-ddrescue] Hard drive / ddrescue expert

[n schembr]

I'm in the process of recovering a dead disk and this has brought  the 
following questions.

Background:
I tend to run spinrite on the  dead drives first. The dynastat process seem to 
recover data that has bit rot.

I then run ddrescue -n   /dev/sda /dev/sdb to fast clone the drives.
I then run ddrescue -r 1 /dev/sda /dev/sdb to see if there is anything else. 



Q1:Hard Disk - Are drive access commands queued?

Q2: Hard Disk -  On modern hard disks is a read  enough  for  a drive 
controller  to detect  a  sector is going bad and replace it with a spare?

Q3: ddrescue - Can dd or ddrescue be used on a single byte of the raw disk to 
refresh it?  ex: ddrescue -n /dev/sda /dev/sda --block-size=1

Q4: ddrescue - Can the disk be mounted and active? Are there any risks?

Q5: Os - Is there a way to refresh the disks at the os level (linux/bsd/unix)?

Yes, I know I can use raid to swap disks. It is my goal to prevent or detect 
the error before the drive fails.


Nick