When your disk has crashed and you try to copy it over to another one,
you'll find out that standard Unix tools like cp, cat, and dd will abort
on every I/O error. dd_rescue does not and helps you to recover the data
that's still available.
The included tool dd_rhelp automates the process to copy around bad spots
from both sides leveraging dd_rescue's ability to copy backwards.
You can also use dd_rescue to destroy data by overwriting multiple times
with pseudo random numbers.