Thank you for the extensive explanation.
I have always been aware that they are several levels of abstraction
between the hardware and the application software, but I was not aware of
the philosophy behind the design of ddrescue, particularly in respect of
the stringent requirement for portability between dissimilar platforms.
That said, I would have thought that the subject ATA commands would have
been supported at least in earlier times. In any case, it does appear that
modern drives do not permit external control over their retry behaviour, at
least not via standard ATA commands. No doubt they have vendor specific
commands that achieve this end -- that's how commercial hardware based
imagers appear to work. In fact these can image a drive at the physical CHS
level, and they are also able to switch off a bad head and image the
remainder. Clearly that's not possible with an ATA tool.
Sorry for my ignorance, and yes, I do understand the distinction. :-)
-Franc
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