raid1

I have outlined below the steps taken to move from a normal single disk system and convert to a raid1 using an additional drive:

Note: /boot cannot be on lvm nor any other raids other than raid1 partition.

Don't forget to make the essential backups prior.

Convert / to raid/lvm

1. fdisk /dev/sdb and make clone of sda (convert partition type to "Linux raid autodetect")
   
2. add /dev/sdb1 -- /boot - 13 blocks (100Mb) - type raid
   
3. add /dev/sdb2 -- rest - type raid
   
4. Create raid partitions:
   
   partprobe
mdadm -C /dev/md0 --auto=yes -l 1 -n 2 missing /dev/sdb1
mdadm -C /dev/md1 --auto=yes -l 1 -n 2 missing /dev/sdb2

5. Create logical volume and copy / partition and /dev files over:
   
   pvcreate /dev/md1
vgcreate vg0 /dev/md1
lvcreate -L 4G -n lv0 vg0
mke2fs -j /dev/vg0/lv0
mkdir /mnt/lv0
mount /dev/vg0/lv0 /mnt/lv0
find / -xdev | cpio -pvmd /mnt/lv0
cp -aux /dev /mnt/lv0

6. Edit /mnt/lv0/etc/fstab to reflect the new root
   
   /dev/vg0/lv0            /                       ext3    defaults        1 1

7. Chroot to new filesystem an create initrd with raid and lvm support
   
   chroot /mnt/lv0
mount -t proc /proc /proc
mount -t sysfs /sys /sys
vgscan
vgchange -ay
mkinitrd -v /boot/initrd-2.6.18-92.1.6.el5.lvm.img 2.6.18-92.1.6.el5

8. Edit grub.conf to point to new root /dev/vg0/lv0
   
9. reboot

Convert /boot to raid1