dd_rescue is a dd tool with following features suitable for rescuing data from
a medium with errors.

- Don't abort on errors on the input file unless the user specify the maximum
  error number.
- Don't truncate the output file.
- Can use two different block sizes for normal operation and the case of errors.
- Can start from the end of the file and move backwards.

WWW: http://www.garloff.de/kurt/linux/ddrescue/