How do you set up RAID1 with both disks bootable on Debian/Ubuntu?

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http://serverfault.com – In Debian 6, new installation, what is the recommended way of setting up a software RAID1 array so that the system is bootable from both disks? I have heard that people that don't know what they are doing may set it up in such a way that the system becomes unbootable if the primary disk fails (!) I haven't been able to find a simple listing of steps for the latest version of Debian. (HowTos)