fzabkar wrote:
@lcoughey, in the absence of a log file, and in the absence of a file system analysis, there would be no way for you or any tool to determine whether a particular sector in an image file contained recovered data or otherwise. Assuming the image file were written to a good drive, then it would contain no unreadable sectors, in which case ddrescue would make a perfect copy of it on a third destination. Without a log file, ddrescue would have no way of knowing if sector X in the image file were zero filled, or contained a "BAD" signature, or if it simply contained the stale data that existed on the drive before the image file was written. All readable sectors in the file would be imaged to the third destination as is, regardless of their contents. Therefore the new log file would register 100% success, ie it would be a pointless exercise.
I've used the auto generate to create a log file many times over...it has always worked. But, I always write to a blank drive and don't write any patterns to the unread sectors. If you wrote a pattern to the unread sectors (ie, unread), you would need to add another step of searching those sectors our and overwriting them with zeros....then generate the log.
Ddrescue doesn't look for fill patterns or analyse the data in any way before copying a sector. Therefore, in the absence of the original logs, it would be nonsensical to run ddrescue against two image files in the expectation that you could somehow merge them. All you would be doing is verifying whether the image files themselves occupy bad sectors.
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