Ddrescue

Ddrescue is a data recovery tool. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying hard to rescue data in case of read errors.

The basic operation of ddrescue is fully automatic. That is, you don't have to wait for an error, stop the program, restart it from a new position, etc.

If you use the mapfile feature of ddrescue, the data is rescued very efficiently, (only the needed blocks are read).

Also you can interrupt the rescue at any time and resume it later at the same point.

The mapfile is an essential part of ddrescue's effectiveness. Use it unless you know what you are doing.