Setup software RAID1 array on running CentOS 6.3 using mdadm. (Multiple Device Administrator)
All commands run from terminal as super user.Default CentOS 6.3 installation with two hard drives, /dev/sda and /dev/sdb which are identical in size. Machine
name is “serverbox.local”. /dev/sdb is currently unused, and /dev/sda has the following partitions:
/dev/sda1: /boot partition, ext4;
/dev/sda2: is used for LVM (volume group vg_serverbox) and contains / (volume root), swap(volume swap_1) and /home (volume home). Final RAID1 configuration:
/dev/md0 (made up of /dev/sda1 and /dev/sdb1): /boot partition, ext4;
/dev/md1 (made up of /dev/sda2 and /dev/sdb2): LVM (volume group vg_serverbox), contains / (volume root), swap (volume swap_1) and /home (volume home).1. Gather information about current system.
Report the current disk space usage:df -h
View physical disks:
fdisk -l
View physical volumes on logical disk partition:
pvdisplay
View virtual group details:
vgdisplay
View Logical volumes:
lvdisplay
Load kernel modules (to avoid a reboot):
modprobe linear modprobe raid0 modprobe raid1
Verify personalities:
cat /proc/mdstat
The output should look as follows:
serverbox:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] unused devices: <none>
2. Preparing /dev/sdb
To create a RAID1 array on a running system, prepare the /dev/sdb hard drive for RAID1, then copy the contents
of /dev/sda hard drive to it, and finally add /dev/sda to the RAID1 array.
Copy the partition table from /dev/sda to /dev/sdb so that both disks have exactly the same layout:
sfdisk -d /dev/sda | sfdisk –f /dev/sdb
Verify both disks are partitioned identically:
fdisk -l
Change the partition type of partitions on /dev/sdb to Linux raid autodetect:
fdisk /dev/sdb
serverbox:~# fdisk /dev/sdb
Command (m for help): t [t = change a partition's system id]
Partition number (1-5): 1
Hex code (type L to list codes): fd [fd = Linux raid auto]
Command (m for help): t Partition number (1-5): 2
Hex code (type L to list codes): fd
Command (m for help): w [w = write changes to disk]
Verify changes written successfully:
fdisk -l
Remove any previous RAID installations on /dev/sdb : (error displayed if none exist)
mdadm --zero-superblock /dev/sdb1 mdadm --zero-superblock /dev/sdb2
3. Creating RAID Arrays
Create RAID arrays /dev/md0 and /dev/md1. /dev/sdb1 will be added to /dev/md0 and/dev/sdb2 to /dev/md1.
mdadm --create /dev/md0 --metadata=0.90 --level=1 --raid-disks=2 missing /dev/sdb1 mdadm --create /dev/md1 --metadata=0.90 --level=1 --raid-disks=2 missing /dev/sdb2
Verify array created: ([_U] or [U_] means that an array is degraded while [UU] means that the array is ok)
cat /proc/mdstat
Create a file system (ext4) on our non-LVM RAID array /dev/md0:
mkfs.ext4 /dev/md0
Logical volumes:
Initialize physical volume /dev/md1 for LVM: (Logical Volume Manager)
pvcreate /dev/md1
Add /dev/md1 to our volume group vg_serverbox:
vgextend vg_serverbox /dev/md1
Verify array /dev/md1 added to logical volume group:
pvdisplay
Review volume group details: (optional)
vgdisplay
Update configuration file /etc/mdadm.conf :
cp /etc/mdadm.conf /etc/mdadm.conf_orig mdadm --examine --scan >> /etc/mdadm.conf
Review the updated configuration file: (Array devices added at end.)
Modify file /etc/fstab. Replace /dev/sda1 with /dev/md0 so that the line looks as follows:
gedit /etc/fstab
[...]
/dev/md0 /boot ext4 defaults 0 2
[...]
Modify file /etc/mtab. Replace line containing /dev/sda1 with /dev/md0:
gedit /etc/mtab
[...]
/dev/md0 /boot ext3 rw 0 0
[...]
Open /boot/grub/menu.lst and add fallback 1 right after default 0:
gedit /boot/grub/menu.lst
[...]
default 0
fallback 1
[...]
Duplicate first kernel stanza [title ...savedefault]. In first stanza; replace root (hd0,0) with root (hd1,0):
[...]
title Vg_serverbox GNU/Linux, kernel 2.6.18-6-686 root (hd1,0)
kernel /vmlinuz-2.6.18-6-686 root=/dev/mapper/vg_serverbox-root ro initrd /initrd.img-2.6.18-6-686
savedefault
title Vg_serverbox GNU/Linux, kernel 2.6.18-6-686 root (hd0,0)
kernel /vmlinuz-2.6.18-6-686 root=/dev/mapper/vg_serverbox-root ro initrd /initrd.img-2.6.18-6-686
savedefault
[...]
Rebuild initramfs using mdadm.conf: https://wiki.ubuntu.com/Initramfs
mv /boot/initramfs-$(uname –r).img /boot/initramfs-$(uname –r).img.old
dracut --mdadmconf --force /boot/initramfs-$(uname –r).img $(uname –r)
4. Moving Data to the RAID Arrays
Copy data from boot partition /dev/sda1 to array /dev/md0: (assuming /dev/sda1 is mounted at /boot)
mkdir /mnt/raid
mount /dev/md0 /mnt/raid
cd /boot; find . –depth | cpio –pmd /mnt/raid
touch /mnt/raid/.autorelabel
sync
umount /mnt/raid
Move the contents of LVM partition /dev/sda2 to LVM RAID array /dev/md1: (takes approx. 45 min. for 200 GB)
pvmove /dev/sda2 /dev/md1
Remove /dev/sda2 from the volume group vg_serverbox:
vgreduce vg_serverbox /dev/sda2
Remove volume /dev/sda2 from LVM:
pvremove /dev/sda2
Verify /dev/md1 is the only physical volume for volume group vg_serverbox:
Change the partition type of /dev/sda2 to Linux raid autodetect:
fdisk /dev/sda
Command (m for help): t Partition number (1-5): 2
Hex code (type L to list codes): fd Command (m for help): w
The partition table has been altered!
Add /dev/sda2 to /dev/md1 array: (Takes approx. 35 min. for 200 GB array to be rebuilt)
mdadm --add /dev/md1 /dev/sda2
Monitor rebuild in progress: (To leave watch, press CTRL+C.)
watch –n 5 cat /proc/mdstat
5. Preparing GRUB
Install the GRUB bootloader on the hard drive /dev/sda and /dev/sdb:
grub
grub>
root (hd0,0)
setup (hd0)
root (hd1,0)
setup (hd1)
quit
Verify system will boot:
reboot
After system reboots verify /dev/md0 is mounted at /boot:
Verify arrays are active: (status should be /dev/md1 [UU] and /dev/md0 [_U] )
cat /proc/mdstat
Verify logical volumes using pvdisplay, vgdisplay, and lvdisplay : (optional)
pvdisplay
vgdisplay
lvdisplay
Change the partition type of /dev/sda1 to Linux raid autodetect: fdisk /dev/sda
Command (m for help): t Partition number (1-5): 1
Hex code (type L to list codes): fd Command (m for help): w
Add /dev/sda1 to the /dev/md0 RAID array: (takes < 1 min.) mdadm --add /dev/md0 /dev/sda1
Verify both volumes are active and running [UU]:
cat /proc/mdstat
Update /etc/mdadm.conf :
cp /etc/mdadm.conf_orig /etc/mdadm.conf mdadm --examine --scan >> /etc/mdadm.conf
Reboot the system:
reboot
That's it - software RAID1 array is active and running!
Testing and rebuilding
Physically remove drive from system, or; Simulate a hard drive failure. [ /dev/sdb ]
mdadm --manage /dev/md0 --fail /dev/sdb1 mdadm --manage /dev/md1 --fail /dev/sdb2 mdadm --manage /dev/md0 --remove /dev/sdb1 mdadm --manage /dev/md1 --remove /dev/sdb2
Shut down the system:
shutdown -h now
Reboot: System should boot in degraded state. Verify array is active but degraded: ( [_U] or [U_] )
cat /proc/mdstat
Shut down the system:
shutdown -h now
Put in a new /dev/sdb drive, or if failure of /dev/sda, move /dev/sdb to failed /dev/sda slot and connect the new
HDD as /dev/sdb. Boot the system.
Verify /dev/sda is boot device and /dev/sdb is empty.
fdisk -l
Copy the partition table of /dev/sda to /dev/sdb:
sfdisk -d /dev/sda | sfdisk –f /dev/sdb
Remove any remains of the RAID array from /dev/sdb:
mdadm --zero-superblock /dev/sdb1 mdadm --zero-superblock /dev/sdb2
Add /dev/sdb to the RAID array: mdadm -a /dev/md0 /dev/sdb1 mdadm -a /dev/md1 /dev/sdb2
Monitor the rebuilding process:
watch –n 5 cat /proc/mdstat
Wait until the synchronization has finished: Install the bootloader on both HDDs:
grub
grub>
root (hd0,0) setup (hd0) root (hd1,0) setup (hd1) quit
That's it. Failed hard drive in RAID1 array is replaced.
