Cloning a drive whilst booted from it

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http://superuser.com – I have a laptop with two drive bays. I want to clone drive one, which is my boot drive running openSuse to the 2nd drive. Is it possible to do when running the os from the boot drive and if so what tool should I use? If it is not possible I do have a third drive which I could boot from, then clone from drive 2 to drive 3, again not sure what tool to use to do a low level disk clone? (HowTos)