How to Setup Software Raid after the fact

If you ever need to setup Software Raid on a box after you have already installed your Distro you can following the steps below.

# mdadm will ask which MD arrays are needed for the root fs. Go with the default (all)

yum install mdadm initramfs-tools vim

# Add raid1 to /etc/modules

echo "raid1" >> /etc/modules

# Regenerate initrd.img file

mkinitramfs -o /boot/test -r /dev/mapper/pve-root

# Rename old img file (replace .x for whatever kernel version you are using)

mv /boot/initrd.img-2.6.18-2-pve /boot/initrd.img-2.6.18-2-pve.original

# Rename new img file

mv /boot/test /boot/initrd.img-2.6.18-2-pve

# Make sure grub is setup on both hdds

grub-install --no-floppy /dev/sda

grub-install --no-floppy /dev/sdb

# Change UUID for (hd0,0) on /boot/grub/menu.1st if your file has the UUID in it.

# This most likely involves replacing the root UUID=XXXXX line with root hd(0,0)

# nano /boot/grub/menu.1st

# Change UUIDs for proper md0 devices on /etc/fstab if your file has the UUID in it.

# Now do the same thing for the /etc/fstab file.

# Replace the UUID=XXXXXXXXX /boot ext3 defaults 0 1 line with /dev/md0 /boot ext3 defaults 0

# nano /etc/fstab

# Clone the partition table from 1st drive to 2nd

sfdisk -d /dev/sda | sfdisk --force /dev/sdb

# Create md devices with second drive only

mdadm --create /dev/md0 --level=1 --raid-devices=2 missing /dev/sdb1

mdadm --create /dev/md1 --level=1 --raid-devices=2 missing /dev/sdb2

# Save new mdconf file

mdadm --detail --scan >> /etc/mdadm/mdadm.conf

# Get boot device setup

mkfs.ext3 /dev/md0

mkdir /mnt/md0

mount /dev/md0 /mnt/md0

cp -ax /boot/* /mnt/md0

umount /mnt/md0

umount /boot; mount /dev/md0 /boot

sfdisk --change-id /dev/sda 1 fd

mdadm --add /dev/md0 /dev/sda1

# Setup data device

pvcreate /dev/md1

vgextend pve /dev/md1

# this step takes a LOOOOONG time

pvmove /dev/sda2 /dev/md1

vgreduce pve /dev/sda2

sfdisk --change-id /dev/sda 2 fd

mdadm --add /dev/md1 /dev/sda2