There are two similar tools for a dd on bad hardware:
What is the difference between dd_rescue and ddrescue, when to prefer which one?
asked Nov 23, 2017 at 23:11
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2related: What's the difference between ddrescue, gddrescue, and dd_rescue?– sebasthNov 23, 2017 at 23:44
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@sebasth Thank you for the link. In the ubuntu question it is rather discussed why there are 3 names. The answer is, ubuntu invented the third. There is no discussion about the functionality. This makes sense, if the question is on askubuntu and not the unix.sx.– Jonas SteinNov 26, 2017 at 13:57
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Someone suggested to close this question, but forgot to add a hint here how to improve the question in her/his opinion.– Jonas SteinNov 26, 2017 at 13:59
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1 Answer
GNU ddrescue first quickly copies good blocks using a large block size and then optionally tries to recover more data reading smaller blocks within the blocks that failed in the first pass. This requires a log file that records what areas are still missing and the output must go to a file or disk that allows random access. If run again with the log file present, ddrescue will try again reading the missing parts only.
Kurt Garloff's dd_rescue copies the data in sequential order, allowing it to be captured on stdout, e.g. to compress it before writing it to a file. When a read error is encountered dd_rescue switches temporarily to a smaller block size to try to recover data from the problematic area before continuing with the remainder of the disk.
