Le primidi 21 brumaire, an CCXXV, Andy Smith a écrit :
You are better off using GNU ddrescue for taking images of
possibly-failing devices.
IIRC, there is a catch there: there is another program with a very
similar name that does not work the same way. Be careful when installing
it.
Amongst other issues, dd will either give up or produce zeroes when
it encounters problems whereas ddrescue will keep track of where it
was unable to read and keep trying.
For the record, when using dd to copy data from a damaged medium, always
use conv=noerror,sync. Without noerror, dd would stop at the first
error and without sync it would just skip the block, making the dump
useless.
But of course, as you say, ddrescue keeps a log of the parts that could
not be read, which is even more useful.
Also, I would advise to dump to a file, not a raw partition.