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Why does ddrescue only read at random places?
Because ddrescue needs to read and write at random places, it only works on seekable (random access) input and output files. If your system supports it, ddrescue can use direct disc access to read the input file, bypassing the kernel cache.
What does ddrescue do to the input file?
If your system supports it, ddrescue can use direct disc access to read the input file, bypassing the kernel cache. Ddrescue also features a ‘fill mode’ able to selectively overwrite parts of the output file, which has a number of interesting uses like wiping data, marking bad areas, or even, in some cases, “repair” damaged sectors.
Why does ddrescue try to minimize head movement?
Therefore, newer versions try to minimize head movement to minimize drive damage. Ddrescue manages efficiently the status of the rescue in progress and tries to rescue the good parts first, scheduling reads inside bad (or slow) areas for later. This maximizes the amount of data that can be finally recovered from a failing drive.
What happens in the first pass of ddrescue?
The first pass reads the non-tried parts of the input file, marking the failed blocks as non-trimmed and skipping beyond them. The second pass delimits the blocks skipped by the first pass. The first two passes also skip beyond slow areas. The skipped areas are tried later in one or three additional passes (before trimming).
What’s the difference between DD and GNU ddrescue?
GNU ddrescue is not a derivative of dd, nor is related to dd in any way except in that both can be used for copying data from one device to another. The key difference is that ddrescue uses a sophisticated algorithm to copy data from failing drives causing them as little additional damage as possible.
How often to retry bad sectors in ddrescue?
-r3 tells ddrescue to retry bad sectors 3 times before giving up. Note: On a failing drive you may want to eliminate this option the first time so as to not waste time hammering on bad sectors and risking drive failure. You can always use the logfile to go back and retry the bad sectors after you get an image from the first sweep.
What does ddrescue do for a failing drive?
Ddrescue manages efficiently the status of the rescue in progress and tries to rescue the good parts first, scheduling reads inside bad (or slow) areas for later. This maximizes the amount of data that can be finally recovered from a failing drive.