Migrating a Linux boot partition to RAID-1

Alexander Hajnal

2 Assumptions

You have experience with administering a Linux or Unix system from the command line. You should also be comfortable with editing configuration files using a text editor.
While following these directions it is fairly easy to inadvertently leave your system in an unbootable state. It is therefor highly recommended that you have a rescue boot floppy or CD handy and that you know how to use it to bring your system back to a bootable state. I also recommend having copies of the Linux Bootable Business Card and Knoppix on hand.
You know what partitions, primary and secondary IDE buses, master and slave drives are and are familiar with how physical devices are named (e.g. /dev/hda).
You feel comfortable with making changes to your computer's hardware.
You have physical access to the machine that you want to convert.
You are using IDE drives on an IBM-compatible PC.
You have root access to the machine.
All commands mentioned in this document need to be run by root
Linux is already installed on the system that you want to convert.
You are running a 2.4.0 or later kernel or are willing to upgrade to one.
The kernel used in this text is 2.4.20 but any of the 2.4.x kernels should work fine. The steps below may also work for 2.6.x kernels but this has not been tested.
You are familiar with building a Linux kernel from source.
If you do not feel comfortable with compiling a kernel from source, you can still use this document if your Linux distribution supplies a kernel with the native Linux RAID-1 drivers. The drivers must be compiled into the kernel, using modules will not work for the method described in this document.
Your bootloader is lilo
Your boot device is the master disk on the primary IDE bus (/dev/hda)
Your disk has a single partition containing the entire root filesystem (/dev/hda1).
This technique will also work if:
- You have currently have a swap partition defined and you replace it with a swapfile.
- You currently have filesystems on more than one partitition on the boot drive. You will need to combine them into a single partition or create separate raid arrays for each partition.
Both of these cases are straighforward to handle; see the FAQ for more information on how to do this.