Coverting Linux System From Non Raid Disk To Software Raid (mdadm)

23 Sep 2012

Tested On

OS: CentOS 6.3 i386
mdadm version: v3.2.3
Hardware: Virtual Machine (VirtualBox 4.1.22)

Introduction

mdadm is a linux software raid implementation. With mdadm you can build software raid from different level on your linux server, in this post I will show how to convert an existing OS system to raid 1 for fault tolerance.

Pre conversion system

df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
                      2.5G  812M  1.6G  34% /
tmpfs                 250M     0  250M   0% /dev/shm
/dev/sda1             485M   85M  375M  19% /boot

Converting to raid 1

fdisk /dev/sdb

Command (m for help): n -> **enter**
Command action
   e   extended
   p   primary partition (1-4)
p -> enter
Partition number (1-4): 1 -> **enter**
First cylinder (1-1044, default 1): **enter**
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-1044, default 1044): +3G **enter**

Command (m for help): **t**
Selected partition 1
Hex code (type L to list codes): **fd**
Changed system type of partition 1 to fd (Linux raid autodetect)

Command (m for help): **a**
Partition number (1-4): **1**

Command (m for help): **w**
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
yum install mdadm -y
mdadm --create /dev/md0 --level raid1 --raid-disks 2 missing /dev/sdb1 --metadata 1.0
echo "MAILADDR [email protected]" >> /etc/mdadm.conf
mdadm --detail --scan >> /etc/mdadm.conf
mkfs.ext4 /dev/md0
mount /dev/md0 /mnt
cd /
find . -xdev | cpio -pm /mnt/
cd /boot
find . -xdev | cpio -pm /mnt/boot/
vi /mnt/etc/fstab
/dev/md0        /                       ext4    defaults        1 1
tmpfs           /dev/shm                tmpfs   defaults        0 0
devpts          /dev/pts                devpts  gid=5,mode=620  0 0
sysfs           /sys                    sysfs   defaults        0 0
proc            /proc                   proc    defaults        0 0
cat /etc/fstab
/dev/mapper/VolGroup-lv_root                    /                       ext4    defaults        1 1
UUID=d898d82b-bb81-4ff5-9261-681b66bc9c7d       /boot                   ext4    defaults        1 2
/dev/mapper/VolGroup-lv_swap                    swap                    swap    defaults        0 0
tmpfs                                           /dev/shm                tmpfs   defaults        0 0
devpts                                          /dev/pts                devpts  gid=5,mode=620  0 0
sysfs                                           /sys                    sysfs   defaults        0 0
proc                                            /proc                   proc    defaults        0 0
grub
grub> device (hd0) /dev/sdb
grub> root (hd0,0)
grub> setup (hd0)
grub> quit
vi /mnt/boot/grub/grub.conf
default=0
timeout=5
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.32-279.5.2.el6.i686)
        root (hd0,0)
        kernel /boot/vmlinuz-2.6.32-279.5.2.el6.i686 ro root=/dev/md0 rd_NO_LUKS LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto quiet KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /boot/initramfs-2.6.32-279.5.2.el6.i686.img
cat /boot/grub/grub.conf
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.32-279.5.2.el6.i686)
        root (hd0,0)
        kernel /vmlinuz-2.6.32-279.5.2.el6.i686 ro root=/dev/mapper/VolGroup-lv_root rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto quiet rd_LVM_LV=VolGroup/lv_root  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM
        initrd /initramfs-2.6.32-279.5.2.el6.i686.img
cd /mnt/boot
mkinitrd --preload raid1 --with=raid1 raid-ramdisk 2.6.32-279.5.2.el6.i686
mv initramfs-2.6.32-279.5.2.el6.i686.img initramfs-2.6.32-279.5.2.el6.i686.img.bck
mv raid-ramdisk initramfs-2.6.32-279.5.2.el6.i686.img
reboot
fdisk /dev/sda

Command (m for help): d -> enter
Partition number (1-4): 2 -> enter

Command (m for help): d -> enter
Selected partition 1

Command (m for help): n -> enter
Command action
   e   extended
   p   primary partition (1-4)
p -> enter
Partition number (1-4): 1 -> enter
First cylinder (1-522, default 1): enter
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-522, default 522): +3G -> enter

Command (m for help): t -> enter
Selected partition 1
Hex code (type L to list codes): fd -> enter
Changed system type of partition 1 to fd (Linux raid autodetect)

Command (m for help): a -> enter
Partition number (1-4): 1 -> enter

Command (m for help): w -> enter
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
yum install parted -y
partprobe /dev/sda
Add /dev/sda1 to the array
mdadm /dev/md0 --add /dev/sda1
cat /proc/mdstat
grub
grub> device (hd0) /dev/sda
grub> root (hd0,0)
grub> setup (hd0)
grub> quit
reboot

Testing Our New Raid 1

mdadm --detail /dev/md0
mdadm --manage --set-faulty /dev/md0 /dev/sda1
tail /var/log/messges

Sep 23 21:27:36 centos-62-1 kernel: md/raid1:md0: Disk failure on sda1, disabling device.
Sep 23 21:27:36 centos-62-1 kernel: md/raid1:md0: Operation continuing on 1 devices.
mdadm --detail /dev/md0
cat /proc/mdstat
mdadm /dev/md0 -r /dev/sda1
mdadm /dev/md0 -a /dev/sda1
mdadm --detail /dev/md0
cat /proc/mdstat

Please visit https://raid.wiki.kernel.org for more information about linux software raid configuration and usage.