I got most of this info from: https://help.ubuntu.com/community/DataRecovery
Install with:
sudo apt-get install gddrescue
Find the disk to rescue with:
sudo fdisk -l
Then run the command using a command like this:
sudo ddrescue -r 5 /dev/sdf /tank/Backup/image /tank/Backup/logfile
In this case 5 is the number of retries attempted to read the data before giving up, /dev/sdf is the path to the device that you found via fdisk -l /tank/Backup/image is the image file that will be written. /tank/Backup/logfile is a logfile that is kept of the recovery.
If the backup is interrupted or you want to run it for another pass with hopes of recovering more information use a command like this:
sudo ddrescue -r 5 -C /dev/sdf /tank/Backup/image /tank/Backup/logfile
Note the -C which tells ddrescue to pickup where it left off, or try to fill in the blocks that are missing
