This document explains how to convert the boot disk of a Linux system to a bootable RAID-1 (mirrored) array. It shows a cookbook approach to setting up such an array and is not meant to explore all of the intricacies of RAID on Linux. This document covers the native Linux RAID drivers, not the Promise drivers. Some people have reported success with setting up the Promise-supplied drivers; I am not one of these people.
Though this document covers converting a very specific configuration to RAID-1, the basic steps can be adapted by an experienced user to more complex configurations. There is some information on how to do this in the FAQ. The Linux distribution used for the examples is Debian; for other distributions the basic steps are the same but file locations, package names, etc. may differ.