Since dd_rhelp only exists to aid operate with dd_rescue, I decided to join the two packages in this thread.
dd_rescue: https://www.garloff.de/kurt/linux/ddrescue/
dd_rhelp: http://www.kalysto.org/utilities/dd_rhelp/index.en.html
dd_rescue is a tool suitable for rescuing data from a medium with errors, i.e. a hard disk with some bad sectors.
dd_rhelp will use dd_rescue on your entire disc, BUT it will
try to gather the maximum valid data before trying for ages on bunches
of badsectors. So if you leave dd_rhelp work for infinite time, it'll
have the same effect as a simple dd_rescue. But because you might not
have this infinite time (this could indeed take really long in some
cases... ), dd_rhelp will come to help.