This Question - Getting loads of Open error 5's when using Terminal to repair permissions - raises the question,
Does mounting a drive in Target Disk Mode bypass SMART, preventing any lockout if the disk is failing & you need to recover data?
In the past, I have always put suspected failing drives [often Windows NTFS drives] in a USB enclosure & attached to my Mac to scavenge/repair, as that way I am ignoring both SMART & any OS intervention from Windows etc.
For a Mac, would Target Disk Mode be just the same as an external USB for similar tasks, or could SMART potentially restrict operations?
Edit: Google would seem to think that SMART reporting cannot be carried over USB or Firewire, but that doesn't exclude the possibility of Thunderbolt. I cannot find any canonical answer even to the first two, though.