When booted into a live session, type: fdisk -l in a terminal as root or sudo to see the device names. If the target is the first drive it will be /dev/sda, /dev/sdb for the second drive. Issue command: dd if=/dev/sda of=/dev/sdb conv=notrunc,noerror as root or sudo, wait till the prompt returns. Depending on the amount of ram, size of processor, it could take up to an hour per 10GB to write, so be patient, if the hard drive light is blinking, it's still working.
If only copying a partition and not the entire drive you will need to adjust the command accordingly.