How to make duplicate of whole HDD [duplicate]

How to make duplicate of whole HDD [duplicate] References This question already has an answer here: What is the best way to clone a linux partition onto a smaller partition? 2 answers I have ubuntu 12.04 production server with 500 gb (nearly 15 gb used) hdd. I want to duplicate whole hdd including it\'s partitions structure, data to another hdd with 400 gb size so that changing hdd will not affect working system. Which tool is the best solution for this task?