When trying to recover data from old failed hard disk, I managed to get it detected by BIOS. I didn’t have ddrescue prepared so I tried using dd, in case the disk won’t start again next time. I tried copying random parts like this:
dd if=/dev/sdb of=dump00000mb.bin bs=1k skip=0k
dd if=/dev/sdb of=dump01000mb.bin bs=1k skip=1000k
dd if=/dev/sdb of=dump05000mb.bin bs=1k skip=5000k
dd if=/dev/sdb of=dump05100mb.bin bs=1k skip=5100k
...
Each time it run until first error. I copied about 10% of disk this way, in many parts. Then during the next days I run proper ddrescue and copied most of the disk to dump.bin. When checking the ddrescue mapfile, some of the partial dumps covered sectors that ddrescue couldn’t read. How can I merge these partial dumps with ddrescue dump?
In ddrescue documentation there is an example how to shift mapfile and image file, when you first ddrescue a partition and later want to rescue the whole drive. In this case I want to shift only the small dump file, so this doesn’t apply here. Even if I’ve shifted the mapfile backwards to match the small dump file, this would delete mapfile contents before this point (mapfile cannot have negative offsets).
