Best way to mirror two drives

[Lance Hoffmeyer]

I just purchased a second 30G drive that I want to use as part of my backup strategy.  I now have two 30G drives in my computer.  I don't have a RAID card.  I have /dev/hda and /dev/hdb.  What is the best way to mirror /dev/hda? I have thought of   dd cp rsync   but am not sure which method would be most efficient.  Are there other methods I am leaving out?   Lance