Migrating a Linux boot partition to RAID-1

Alexander Hajnal

Copying files and making the array bootable

Reboot the system. As the computer starts up, hold down the Control key until you get the lilo boot prompt. At the prompt, type linux single boot=/dev/hdc root=/dev/hdc1 where /dev/hdc reflects the location of the old drive. When prompted, enter root's password.
Mount the raid array by running mount /dev/md0 /raid
Copy the files from the old partition to the array by running cp -ax / /raid
Update the array's copy of lilo.conf to reflect the array's presence by running cp -a /raid/etc/lilo.conf.raid /raid/etc/lilo.conf
Create a swapfile on the array. For a 256M swap file run dd if=/dev/zero of=/raid/swapfile bs=1024 count=262144 and then mskwap /raid/swapfile

Alter the array's fstab file (/raid/etc/fstab to specify the array as the root filesystem and the swap file. For example, if /etc/fstab on the old disk looked like this:

/dev/hda1   /        ext3     errors=remount-ro  0  0
proc        /proc    proc     defaults           0  0
/dev/fd0    /floppy  auto     user,noauto        0  0
/dev/cdrom  /cdrom   iso9660  ro,user,noauto     0  0
/dev/hda2   none     swap     sw                 0  0

then you should change /raid/etc/fstab to the following:

/dev/md0    /        ext3     errors=remount-ro  0  0
proc        /proc    proc     defaults           0  0
/dev/fd0    /floppy  auto     user,noauto        0  0
/dev/cdrom  /cdrom   iso9660  ro,user,noauto     0  0
/swapfile   none     swap     sw                 0  0

Note that the swap partition has been changed to the swap file created in the previous step.

Mount the array's /boot directory onto the root partition by running mount --bind /raid/boot /boot
This step is very important. If the directory is not mounted then lilo will not write a correct bootloader and the array will not be bootable. The bind option was first introduced in the 2.4.0 kernel.
Mark the the first partition of the new disk as bootable:
- Run cfdisk /dev/hda
- Select [Bootable] and press Enter
- Select [Write] and press Enter
- Type yesEnter
- Select [Quit] and press Enter
Install a bootloader onto the array by running /sbin/lilo -v2 -C /raid/etc/lilo.conf.raid
Reboot the computer. It should now boot off of the array.
Once your system has booted, log in as root and check that you are running off of the array by running mount. You should see that the root partition (/) is physically located on /dev/md0
Add the old drive to the array:
- Edit /etc/raidtab and change failed-disk to raid-disk
- Activate partition in the array by running /sbin/raidhotadd /dev/md0 /dev/hdc1
The array should begin to rebuild itself automatically. The array is immediately usable; you do not have to wait for the rebuild to finish. You can track the rebuild process by running cat /proc/mdstat

When the array has finished rebuild a message will be printed to the console and to syslog. You should see something similar to the following (the sizes and offsets will vary):

md: md0: sync done.
RAID1 conf printout:
 --- wd:1 rd:2 nd:3
(many lines not shown)
RAID1 conf printout:
 --- wd:2 rd:2 nd:3
(many lines not shown)
md: updating md0 RAID superblock on device
md: hdc1 [events: 00000013]<6>(write) hdc1's sb offset: 4210816
md: hda1 [events: 00000013]<6>(write) hda1's sb offset: 4210816
md: recovery thread finished ...

Verify that the array has been built correctly by running cat /proc/mdstat. You should see the following (sizes will vary):
```
Personalities : [raid1]
read_ahead 1024 sectors
md0 : active raid1 hdc1[1] hda1[0]
      4210816 blocks [2/2] [UU]

unused devices: <none>
```
Make sure that the drives listed are hdc1 and hda1 if you see the drives listed as hdc1 and hda, see the FAQ.
Now that the array has finished rebuilding, the install process is complete. Enjoy your new array!