[Bug-ddrescue] Suggestion / feature request - bad head mapping

[Peter Clifton]

Hi,

I've been dumping a disk with ddrescue for a friend, and it occurred to me that 
one feature present in hardware based / proprietary recovery tools (as far as I 
could discern from watching youtube videos of professional recovery), is 
bad-head mapping.

The pattern of slow / bad reads from this particular disk appears to be 75% 
good, 25% bad, in a fairly regular pattern. I know the disk has 2x platters, 4x 
heads, so this suggests (possibly), a damaged region of one platter face, or 
one read head wearing or damaged more significantly than the others.

I was curious as to whether you had suggestion how (or interest in adding a 
feature), to have ddrescue focus on the 3/4 of the disk which is more readily 
accessible.

I understand that LBA to head mapping can very quite significantly between 
different types of drive though, and I have no idea of the techniques used by 
the proprietary disk recovery tools to determine this mapping. (From the video 
I saw, it seemed to be read or determined by scanning the drive somehow.)

Anyhow - also wanted to say thanks for the utility. An improvement over 
dd_rescue, and I'm sure it has saved many people much data. In this case, 
fortunately - the drive was _just_ accessible enough to pull the majority of 
the user files my friend wanted through the filesystem before starting the full 
disk image.

I guess a related (but very advanced) feature one could imagine adding at some 
future point, is persuading ddrescue to focus on sectors of the disk which are 
identified as containing desired filesystem data (as proprietary tools do). 
Obviously this would require connecting with a filesystem driver, so would be 
rather a complex task. Is this kind of functionality on your wish-list for the 
future, or out of scope for ddrescue development?


Kind regards,

Peter