What's the best way to have a backup image of system disk?

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http://serverfault.com – Under windows system I'm used to create an image of HD with driveImageXML. What's the best approach to have an Image of the hard-drive containing the OS, with Ubuntu Server? I'd like to have a snapshot of the current configuration so If ever happens that the primary disk will fail I could simply restore this image on a new HD, unplug the broken one, plug the newly created. Saving me days on setting up and reconfigure the whole Unix server. (HowTos)