HOWTO: Migrate an Existing RAID Array to a New Array

How to migrate from an existing software RAID 1 array to a new RAID 1 array on CentOS 5.5

# File: Migrate_to_new_RAID_Array_on_CentOS_5.5.notes
# Auth: burly
# Date: 11/20/2010
# Refs: 
# Desc: How migrate from one RAID 1 array to a new one
#       on CentOS 5.5

# I booted from a Knoppix CD to do this. In retrospect,
# I should have used a CentOS LiveCD because the
# tooling, versions, and layout of Knoppix are different 
# which caused some issues. Also, because my OS is x86-64
# but Knoppix is x86, I could not chroot into my system 
# environment, which are ultimately required to create the
# initrd files.

# Boot from the Knoppix CD and drop to a shell

# Start up the existing RAID Array (one of the 2 drives
# from the existing RAID 1 array was on sdc for me)
mdadm --examine --scan /dev/sdc1 >> /etc/mdadm/mdadm.conf
mdadm --examine --scan /dev/sdc2 >> /etc/mdadm/mdadm.conf
mdadm --examein --scan /dev/sdc3 >> /etc/mdadm/mdadm.conf
/etc/init.d/mdadm start
/etc/init.d/mdadm-raid start

# Partition first SATA drive in whatever partition numbers
# and sizes you want. Make sure all partitions that 
# will be in an RAID array use ID type "fd" for RAID 
# autodetect and type "82" for swap. Make sure /boot
# is marked with the bootable flag
fdisk /dev/sda
 
# Repeat for the other disks OR if you are using the
# identical setup on each, you can use sfdisk to 
# simplify your life.
sfdisk -d /dev/sda | sfdisk /dev/sdb

# Create the new boot array
# NOTE: If you don't use metadata 0.90 (but instead 
#       1.0 or 1.1) you'll run into problems with grub.
#       In RAID 1, with metadata 0.90, you can mount
#       the fs on the partition without starting RAID.
#       With newer versions of metadata the superblock
#       for RAID gets written at the beginning of the 
#       partition where the filesystem superblock
#       normally would go. This results in the inability
#       to mount the filesystem without first starting
#       RAID. In the case of your boot partition, this 
#       results in the inability to setup grub and thus boot.
mdadm --create --verbose --metadata=0.90 /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1

# Copy everything over for /boot
mkdir /mnt/oldBoot
mkdir /mnt/newBoot
mkfs.ext3 /dev/md0
mount --options=ro /dev/md0 /mnt/oldBoot
cd /mnt/oldBoot
find . -mount -print0 | cpio -0dump /mnt/newBoot

# Make the new swap
mkswap /dev/sda2
mkswap /dev/sdb2

# Create the new array for LVM. I used metadata
# 0.90 again for consistency AND because I believe
# the version of mdadm in CentOS won't handle newer
# versions of it
mdadm --create --verbose --metadata=0.90 /dev/md1 --level=1 --raid-devices=2 /dev/sda3 /dev/sdb3

# Setup LVM2
pvcreate /dev/md1
vgcreate vg /dev/md1
lvcreate -L8G -nroot vg
lvcreate -L10G -nhome vg
lvcreate -L250G -nvm vg

# Format the filesystems.
# NOTE: I fixed the reserved space to 1% (default is 5%)
#       for the VM LV to save some space and 
#       because in larger, non-root partitions, you
#       don't need all that reserved space.
mkfs.ext3 /dev/vg/root
mkfs.ext3 /dev/vg/home
mkfs.ext3 -m 1 /dev/vg/vm


# Copy everything over for /
mkdir /mnt/oldRoot
mkdir /mnt/newRoot
mount --options=ro /dev/vgOS/lvRoot /mnt/oldRoot
mount /dev/vg/root /mnt/newRoot
cd /mnt/oldRoot
find . -mount -print0 | cpio -0dump /mnt/newRoot

# Copy everything over for /home
mkdir /mnt/oldHome
mkdir /mnt/newHome
mount --options=ro /dev/vgOS/lvHome /mnt/oldHome
mount /dev/vg/home /mnt/newHome
cd /mnt/oldHome
find . -mount -print0 | cpio -0dump /mnt/newHome

# Copy everything over for /boot
mkdir /mnt/oldVM
mkdir /mnt/newVM
mount --options=ro /dev/vgOS/lvVM /mnt/oldVM
mount /dev/vg/vm /mnt/newVM
cd /mnt/oldVM
find . -mount -print0 | cpio -0dump /mnt/newVM

# Remove any existing/stale lines in the mdadm.conf file

# Setup the mdadm config on the new /
mdadm -Esb /dev/sda1 >> /mnt/newRoot/etc/mdadm.conf
mdadm -Esb /dev/sda3 >> /mnt/newRoot /etc/mdadm.conf

# Update fstab on the new machine to use the new 
# mount points (e.g. if you changed VolumeGroup or 
# LogicalVolume names)
vim /mnt/newRoot/etc/fstab

# REBOOT TO A CENTOS LIVECD (if you weren't already on one)

# First we chroot
mkdir /mnt/sysimage
mount /dev/vg/root /mnt/sysimage
mount /dev/vg/home /mnt/sysimage/home
mount /dev/md0 /mnt/sysimage/boot
mount --bind /dev /mnt/sysimage/dev
mount -t proc none /mnt/sysimage/proc
mount -t sysfs none /mnt/target/sys
chroot /mnt/sysimage

# Make a new initrd to boot from
cd /boot
mv initrd-2.6.18-194.26.1.el5.img initrd-2.6.18-194.26.1.el5.img.bak
mkinitrd initrd-2.6.18-194.26.1.el5.img  2.6.18-194.26.1.el5

# Setup grub on both of the drives
grub
root(hd0,0)
setup(hd0)
root(hd1,0)
setup(hd1)
quit

# Reboot!