dd

http://superuser.com/questions/246427/why-does-my-dd-backup-of-macbook-os-x-fail-to-boot-upon-restore

sudo dd if=/dev/sdc conv=sync,noerror of=/home/backup.img bs=64K

You will also need to use those options for the restore:

sudo dd if=/home/backup.img of=/dev/sdb conv=sync,noerror bs=64K