dd if=/dev/sdX of=/path/to/backuphardisk.img
dd if=/dev/sdX |gzip > of=/path/to/imageharddisk.gz
dd if=/dev/hdA of=/dev/hdB


A = source
B = target
X = a, b c, device eg. sda, sdb etc.


Restore
dd if=/path/to/image of=/dev/sdX
gzip -dc /path/to/imageharddisk.gz | dd of=/dev/sdX