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How To Set Up Software RAID1 On A Running System (Incl. GRUB2 Configuration) (Ubuntu 10.04)


This guide explains how to set up software RAID1 on an already running Ubuntu 10.04 system. The GRUB2 bootloader will be configured in such a way that the system will still be able to boot if one of the hard drives fails (no matter which one).

I do not issue any guarantee that this will work for you!

 

1 Preliminary Note

In this tutorial I’m using an Ubuntu 10.04 system with two hard drives, /dev/sda and /dev/sdb which are identical in size. /dev/sdb is currently unused, and /dev/sda has the following partitions:

  • /dev/sda1: /boot partition, ext4;
  • /dev/sda2: swap;
  • /dev/sda3: / partition, ext4

In the end I want to have the following situation:

  • /dev/md0 (made up of /dev/sda1 and /dev/sdb1): /boot partition, ext4;
  • /dev/md1 (made up of /dev/sda2 and /dev/sdb2): swap;
  • /dev/md2 (made up of /dev/sda3 and /dev/sdb3): / partition, ext4

This is the current situation:

df -h

root@server1:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda3             4.0G  808M  3.0G  21% /
none                  243M  168K  243M   1% /dev
none                  247M     0  247M   0% /dev/shm
none                  247M   36K  247M   1% /var/run
none                  247M     0  247M   0% /var/lock
none                  247M     0  247M   0% /lib/init/rw
none                  4.0G  808M  3.0G  21% /var/lib/ureadahead/debugfs
/dev/sda1             472M   27M  422M   6% /boot
root@server1:~#

fdisk -l

root@server1:~# fdisk -l

Disk /dev/sda: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000246b7

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          63      498688   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              63         125      499712   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             125         653     4242432   83  Linux
Partition 3 does not end on cylinder boundary.

Disk /dev/sdb: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/sdb doesn’t contain a valid partition table
root@server1:~#

 

2 Installing mdadm

The most important tool for setting up RAID is mdadm. Let’s install it like this:

aptitude install initramfs-tools mdadm

Afterwards, we load a few kernel modules (to avoid a reboot):

modprobe linear
modprobe multipath
modprobe raid0
modprobe raid1
modprobe raid5
modprobe raid6
modprobe raid10

Now run

cat /proc/mdstat

The output should look as follows:

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
unused devices: <none>
root@server1:~#

 

3 Preparing /dev/sdb

To create a RAID1 array on our already running system, we must prepare the /dev/sdb hard drive for RAID1, then copy the contents of our /dev/sda hard drive to it, and finally add /dev/sda to the RAID1 array.

First, we copy the partition table from /dev/sda to /dev/sdb so that both disks have exactly the same layout:

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

The output should be as follows:

root@server1:~# sfdisk -d /dev/sda | sfdisk –force /dev/sdb
Checking that no-one is using this disk right now …
OK

Disk /dev/sdb: 652 cylinders, 255 heads, 63 sectors/track

sfdisk: ERROR: sector 0 does not have an msdos signature
/dev/sdb: unrecognized partition table type
Old situation:
No partitions found
New situation:
Units = sectors of 512 bytes, counting from 0

Device Boot    Start       End   #sectors  Id  System
/dev/sdb1   *      2048    999423     997376  83  Linux
/dev/sdb2        999424   1998847     999424  82  Linux swap / Solaris
/dev/sdb3       1998848  10483711    8484864  83  Linux
/dev/sdb4             0         –          0   0  Empty
Warning: partition 1 does not end at a cylinder boundary
Successfully wrote the new partition table

Re-reading the partition table …

If you created or changed a DOS partition, /dev/foo7, say, then use dd(1)
to zero the first 512 bytes:  dd if=/dev/zero of=/dev/foo7 bs=512 count=1
(See fdisk(8).)
root@server1:~#

The command

fdisk -l

should now show that both HDDs have the same layout:

root@server1:~# fdisk -l

Disk /dev/sda: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000246b7

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          63      498688   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              63         125      499712   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sda3             125         653     4242432   83  Linux
Partition 3 does not end on cylinder boundary.

Disk /dev/sdb: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          63      498688   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sdb2              63         125      499712   82  Linux swap / Solaris
Partition 2 does not end on cylinder boundary.
/dev/sdb3             125         653     4242432   83  Linux
Partition 3 does not end on cylinder boundary.
root@server1:~#

Next we must change the partition type of our three partitions on /dev/sdb to Linux raid autodetect:

fdisk /dev/sdb

root@server1:~# fdisk /dev/sdb

WARNING: DOS-compatible mode is deprecated. It’s strongly recommended to
switch off the mode (command ‘c’) and change display units to
sectors (command ‘u’).

Command (m for help): <– m
Command action
a   toggle a bootable flag
b   edit bsd disklabel
c   toggle the dos compatibility flag
d   delete a partition
l   list known partition types
m   print this menu
n   add a new partition
o   create a new empty DOS partition table
p   print the partition table
q   quit without saving changes
s   create a new empty Sun disklabel
t   change a partition’s system id
u   change display/entry units
v   verify the partition table
w   write table to disk and exit
x   extra functionality (experts only)

Command (m for help): <– t
Partition number (1-4): <– 1
Hex code (type L to list codes): <– L

0  Empty           24  NEC DOS         81  Minix / old Lin bf  Solaris
1  FAT12           39  Plan 9          82  Linux swap / So c1  DRDOS/sec (FAT-
2  XENIX root      3c  PartitionMagic  83  Linux           c4  DRDOS/sec (FAT-
3  XENIX usr       40  Venix 80286     84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
4  FAT16 <32M      41  PPC PReP Boot   85  Linux extended  c7  Syrinx
5  Extended        42  SFS             86  NTFS volume set da  Non-FS data
6  FAT16           4d  QNX4.x          87  NTFS volume set db  CP/M / CTOS / .
7  HPFS/NTFS       4e  QNX4.x 2nd part 88  Linux plaintext de  Dell Utility
8  AIX             4f  QNX4.x 3rd part 8e  Linux LVM       df  BootIt
9  AIX bootable    50  OnTrack DM      93  Amoeba          e1  DOS access
a  OS/2 Boot Manag 51  OnTrack DM6 Aux 94  Amoeba BBT      e3  DOS R/O
b  W95 FAT32       52  CP/M            9f  BSD/OS          e4  SpeedStor
c  W95 FAT32 (LBA) 53  OnTrack DM6 Aux a0  IBM Thinkpad hi eb  BeOS fs
e  W95 FAT16 (LBA) 54  OnTrackDM6      a5  FreeBSD         ee  GPT
f  W95 Ext’d (LBA) 55  EZ-Drive        a6  OpenBSD         ef  EFI (FAT-12/16/
10  OPUS            56  Golden Bow      a7  NeXTSTEP        f0  Linux/PA-RISC b
11  Hidden FAT12    5c  Priam Edisk     a8  Darwin UFS      f1  SpeedStor
12  Compaq diagnost 61  SpeedStor       a9  NetBSD          f4  SpeedStor
14  Hidden FAT16 <3 63  GNU HURD or Sys ab  Darwin boot     f2  DOS secondary
16  Hidden FAT16    64  Novell Netware  af  HFS / HFS+      fb  VMware VMFS
17  Hidden HPFS/NTF 65  Novell Netware  b7  BSDI fs         fc  VMware VMKCORE
18  AST SmartSleep  70  DiskSecure Mult b8  BSDI swap       fd  Linux raid auto
1b  Hidden W95 FAT3 75  PC/IX           bb  Boot Wizard hid fe  LANstep
1c  Hidden W95 FAT3 80  Old Minix       be  Solaris boot    ff  BBT
1e  Hidden W95 FAT1
Hex code (type L to list codes):
 <– fd
Changed system type of partition 1 to fd (Linux raid autodetect)

Command (m for help): <– t
Partition number (1-4): <– 2
Hex code (type L to list codes): <– fd
Changed system type of partition 2 to fd (Linux raid autodetect)

Command (m for help): <– t
Partition number (1-4): <– 3
Hex code (type L to list codes): <– fd
Changed system type of partition 3 to fd (Linux raid autodetect)

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

Calling ioctl() to re-read partition table.
Syncing disks.
root@server1:~#

To make sure that there are no remains from previous RAID installations on /dev/sdb, we run the following commands:

mdadm –zero-superblock /dev/sdb1
mdadm –zero-superblock /dev/sdb2
mdadm –zero-superblock /dev/sdb3

If there are no remains from previous RAID installations, each of the above commands will throw an error like this one (which is nothing to worry about):

root@server1:~# mdadm –zero-superblock /dev/sdb1
mdadm: Unrecognised md component device – /dev/sdb1
root@server1:~#

Otherwise the commands will not display anything at all.

4 Creating Our RAID Arrays

Now let’s create our RAID arrays /dev/md0, /dev/md1, and /dev/md2. /dev/sdb1 will be added to /dev/md0, /dev/sdb2 to /dev/md1, and /dev/sdb3 to /dev/md2. /dev/sda1, /dev/sda2, and /dev/sda3 can’t be added right now (because the system is currently running on them), therefore we use the placeholder missing in the following three commands:

mdadm –create /dev/md0 –level=1 –raid-disks=2 missing /dev/sdb1
mdadm –create /dev/md1 –level=1 –raid-disks=2 missing /dev/sdb2
mdadm –create /dev/md2 –level=1 –raid-disks=2 missing /dev/sdb3

The command

cat /proc/mdstat

should now show that you have three degraded RAID arrays ([_U] or [U_] means that an array is degraded while [UU] means that the array is ok):

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md2 : active raid1 sdb3[1]
4242368 blocks [2/1] [_U]

md1 : active raid1 sdb2[1]
499648 blocks [2/1] [_U]

md0 : active raid1 sdb1[1]
498624 blocks [2/1] [_U]

unused devices: <none>
root@server1:~#

Next we create filesystems on our RAID arrays (ext4 on /dev/md0 and /dev/md2 and swap on /dev/md1):

mkfs.ext4 /dev/md0
mkswap /dev/md1
mkfs.ext4 /dev/md2

Next we must adjust /etc/mdadm/mdadm.conf (which doesn’t contain any information about our new RAID arrays yet) to the new situation:

cp /etc/mdadm/mdadm.conf /etc/mdadm/mdadm.conf_orig
mdadm –examine –scan >> /etc/mdadm/mdadm.conf

Display the contents of the file:

cat /etc/mdadm/mdadm.conf

At the bottom of the file you should now see details about our three (degraded) RAID arrays:

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays

# This file was auto-generated on Mon, 21 Jun 2010 13:21:00 +0200
# by mkconf $Id$
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=68686c40:b924278e:325ecf68:79913751
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=9719181e:3071f655:325ecf68:79913751
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=c3360f0f:7f3d47ec:325ecf68:79913751

 

5 Adjusting The System To RAID1

Now let’s mount /dev/md0 and /dev/md2 (we don’t need to mount the swap array /dev/md1):

mkdir /mnt/md0
mkdir /mnt/md2

mount /dev/md0 /mnt/md0
mount /dev/md2 /mnt/md2

You should now find both arrays in the output of

mount

root@server1:~# mount
/dev/sda3 on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
none on /var/lib/ureadahead/debugfs type debugfs (rw,relatime)
/dev/sda1 on /boot type ext4 (rw)
/dev/md0 on /mnt/md0 type ext4 (rw)
/dev/md2 on /mnt/md2 type ext4 (rw)
root@server1:~#

Next we modify /etc/fstab. Comment out the current /, /boot, and swap partitions and add new lines for them where you replace the UUIDs with /dev/md0 (for the /boot partition), /dev/md1 (for the swap partition) and /dev/md2 (for the / partition) so that the file looks as follows:

vi /etc/fstab

# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
proc            /proc           proc    nodev,noexec,nosuid 0       0
# / was on /dev/sda3 during installation
#UUID=48d65bba-0f02-44b4-8557-b508309b1963 /               ext4    errors=remount-ro 0       1
/dev/md2 /               ext4    errors=remount-ro 0       1
# /boot was on /dev/sda1 during installation
#UUID=e3a677ee-2db0-4a8a-8d6c-94715c8cd90f /boot           ext4    defaults        0       2
/dev/md0 /boot           ext4    defaults        0       2
# swap was on /dev/sda2 during installation
#UUID=1e27f700-ec54-4de9-9428-c6d47d7921f4 none            swap    sw              0       0
/dev/md1 none            swap    sw              0       0
/dev/fd0        /media/floppy0  auto    rw,user,noauto,exec,utf8 0       0

Next replace /dev/sda1 with /dev/md0 and /dev/sda3 with /dev/md2 in /etc/mtab:

vi /etc/mtab

/dev/md2 / ext4 rw,errors=remount-ro 0 0
proc /proc proc rw,noexec,nosuid,nodev 0 0
none /sys sysfs rw,noexec,nosuid,nodev 0 0
none /sys/fs/fuse/connections fusectl rw 0 0
none /sys/kernel/debug debugfs rw 0 0
none /sys/kernel/security securityfs rw 0 0
none /dev devtmpfs rw,mode=0755 0 0
none /dev/pts devpts rw,noexec,nosuid,gid=5,mode=0620 0 0
none /dev/shm tmpfs rw,nosuid,nodev 0 0
none /var/run tmpfs rw,nosuid,mode=0755 0 0
none /var/lock tmpfs rw,noexec,nosuid,nodev 0 0
none /lib/init/rw tmpfs rw,nosuid,mode=0755 0 0
none /var/lib/ureadahead/debugfs debugfs rw,relatime 0 0
/dev/md0 /boot ext4 rw 0 0
/dev/md0 /mnt/md0 ext4 rw 0 0
/dev/md2 /mnt/md2 ext4 rw 0 0

Now up to the GRUB2 boot loader. Create the file /etc/grub.d/09_swraid1_setup as follows:

cp /etc/grub.d/40_custom /etc/grub.d/09_swraid1_setup
vi /etc/grub.d/09_swraid1_setup

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
menuentry 'Ubuntu, with Linux 2.6.32-21-server' --class ubuntu --class gnu-linux --class gnu --class os {
        recordfail
        insmod raid
        insmod mdraid
        insmod ext2
        set root='(md0)'
        linux   /vmlinuz-2.6.32-21-server root=/dev/md2 ro   quiet
        initrd  /initrd.img-2.6.32-21-server
}

Make sure you use the correct kernel version in the menuentry stanza (in the linux and initrd lines). You can find it out by running

uname -r

or by taking a look at the current menuentry stanzas in the ### BEGIN /etc/grub.d/10_linux ### section in /boot/grub/grub.cfg. Also make sure that you use root=/dev/md2 in the linux line.

The important part in our new menuentry stanza is the line set root='(md0)’ – it makes sure that we boot from our RAID1 array /dev/md0 (which will hold the /boot partition) instead of /dev/sda or /dev/sdb which is important if one of our hard drives fails – the system will still be able to boot.

Run

update-grub

to write our new kernel stanza from /etc/grub.d/09_swraid1_setup to /boot/grub/grub.cfg.

Next we adjust our ramdisk to the new situation:

update-initramfs -u

Now we copy the contents of /dev/sda1 and /dev/sda3 to /dev/md0 and /dev/md2 (which are mounted on /mnt/md0 and /mnt/md2):

cp -dpRx / /mnt/md2

cd /boot
cp -dpRx . /mnt/md0

 

6 Preparing GRUB2 (Part 1)

Afterwards we must make sure that the GRUB2 bootloader is installed on both hard drives, /dev/sda and /dev/sdb:

grub-install /dev/sda
grub-install /dev/sdb

Now we reboot the system and hope that it boots ok from our RAID arrays:

reboot

7 Preparing /dev/sda

If all goes well, you should now find /dev/md0 and /dev/md2 in the output of

df -h

root@server1:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/md2              4.0G  815M  3.0G  22% /
none                  243M  192K  243M   1% /dev
none                  247M     0  247M   0% /dev/shm
none                  247M   40K  247M   1% /var/run
none                  247M     0  247M   0% /var/lock
none                  247M     0  247M   0% /lib/init/rw
none                  4.0G  815M  3.0G  22% /var/lib/ureadahead/debugfs
/dev/md0              472M   27M  421M   6% /boot
root@server1:~#

The output of

cat /proc/mdstat

should be as follows:

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdb1[1]
498624 blocks [2/1] [_U]

md1 : active raid1 sdb2[1]
499648 blocks [2/1] [_U]

md2 : active raid1 sdb3[1]
4242368 blocks [2/1] [_U]

unused devices: <none>
root@server1:~#

Now we must change the partition types of our three partitions on /dev/sda to Linux raid autodetect as well:

fdisk /dev/sda

root@server1:~# fdisk /dev/sda

WARNING: DOS-compatible mode is deprecated. It’s strongly recommended to
switch off the mode (command ‘c’) and change display units to
sectors (command ‘u’).

Command (m for help): <– t
Partition number (1-4): <– 1
Hex code (type L to list codes): <– fd
Changed system type of partition 1 to fd (Linux raid autodetect)

Command (m for help): <– t
Partition number (1-4): <– 2
Hex code (type L to list codes): <– fd
Changed system type of partition 2 to fd (Linux raid autodetect)

Command (m for help): <– t
Partition number (1-4): <– 3
Hex code (type L to list codes): <– fd
Changed system type of partition 3 to fd (Linux raid autodetect)

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

Calling ioctl() to re-read partition table.
Syncing disks.
root@server1:~#

Now we can add /dev/sda1, /dev/sda2, and /dev/sda3 to the respective RAID arrays:

mdadm –add /dev/md0 /dev/sda1
mdadm –add /dev/md1 /dev/sda2
mdadm –add /dev/md2 /dev/sda3

Now take a look at

cat /proc/mdstat

… and you should see that the RAID arrays are being synchronized:

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sda1[0] sdb1[1]
498624 blocks [2/2] [UU]

md1 : active raid1 sda2[2] sdb2[1]
499648 blocks [2/1] [_U]
resync=DELAYED

md2 : active raid1 sda3[2] sdb3[1]
4242368 blocks [2/1] [_U]
[===========>………]  recovery = 55.1% (2338176/4242368) finish=0.3min speed=83506K/sec

unused devices: <none>
root@server1:~#

(You can run

watch cat /proc/mdstat

to get an ongoing output of the process. To leave watch, press CTRL+C.)

Wait until the synchronization has finished (the output should then look like this:

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sda1[0] sdb1[1]
498624 blocks [2/2] [UU]

md1 : active raid1 sda2[0] sdb2[1]
499648 blocks [2/2] [UU]

md2 : active raid1 sda3[0] sdb3[1]
4242368 blocks [2/2] [UU]

unused devices: <none>
root@server1:~#

).

Then adjust /etc/mdadm/mdadm.conf to the new situation:

cp /etc/mdadm/mdadm.conf_orig /etc/mdadm/mdadm.conf
mdadm –examine –scan >> /etc/mdadm/mdadm.conf

/etc/mdadm/mdadm.conf should now look something like this:

cat /etc/mdadm/mdadm.conf

# mdadm.conf
#
# Please refer to mdadm.conf(5) for information about this file.
#

# by default, scan all partitions (/proc/partitions) for MD superblocks.
# alternatively, specify devices to scan, using wildcards if desired.
DEVICE partitions

# auto-create devices with Debian standard permissions
CREATE owner=root group=disk mode=0660 auto=yes

# automatically tag new arrays as belonging to the local system
HOMEHOST <system>

# instruct the monitoring daemon where to send mail alerts
MAILADDR root

# definitions of existing MD arrays

# This file was auto-generated on Mon, 21 Jun 2010 13:21:00 +0200
# by mkconf $Id$
ARRAY /dev/md0 level=raid1 num-devices=2 UUID=68686c40:b924278e:325ecf68:79913751
ARRAY /dev/md1 level=raid1 num-devices=2 UUID=9719181e:3071f655:325ecf68:79913751
ARRAY /dev/md2 level=raid1 num-devices=2 UUID=c3360f0f:7f3d47ec:325ecf68:79913751

 

8 Preparing GRUB2 (Part 2)

Now we delete /etc/grub.d/09_swraid1_setup

rm -f /etc/grub.d/09_swraid1_setup

… and update our GRUB2 bootloader configuration:

update-grub
update-initramfs -u

Now if you take a look at /boot/grub/grub.cfg, you should find that the menuentry stanzas in the ### BEGIN /etc/grub.d/10_linux ### section look pretty much the same as what we had in /etc/grub.d/09_swraid1_setup (they should now also be set to boot from /dev/md0 instead of (hd0,1) or (hd1,1)), that’s why we don’t need /etc/grub.d/09_swraid1_setup anymore.

Reboot the system:

reboot

It should boot without problems.

That’s it – you’ve successfully set up software RAID1 on your running Ubuntu 10.04 system!

9 Testing

Now let’s simulate a hard drive failure. It doesn’t matter if you select /dev/sda or /dev/sdb here. In this example I assume that /dev/sdb has failed.

To simulate the hard drive failure, you can either shut down the system and remove /dev/sdb from the system, or you (soft-)remove it like this:

mdadm –manage /dev/md0 –fail /dev/sdb1
mdadm –manage /dev/md1 –fail /dev/sdb2
mdadm –manage /dev/md2 –fail /dev/sdb3

mdadm –manage /dev/md0 –remove /dev/sdb1
mdadm –manage /dev/md1 –remove /dev/sdb2
mdadm –manage /dev/md2 –remove /dev/sdb3

Shut down the system:

shutdown -h now

Then put in a new /dev/sdb drive (if you simulate a failure of /dev/sda, you should now put /dev/sdb in /dev/sda‘s place and connect the new HDD as /dev/sdb!) and boot the system. It should still start without problems.

Now run

cat /proc/mdstat

and you should see that we have a degraded array:

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md2 : active raid1 sda3[0]
4242368 blocks [2/1] [U_]

md1 : active raid1 sda2[0]
499648 blocks [2/1] [U_]

md0 : active raid1 sda1[0]
498624 blocks [2/1] [U_]

unused devices: <none>
root@server1:~#

The output of

fdisk -l

should look as follows:

root@server1:~# fdisk -l

Disk /dev/sda: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000246b7

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          63      498688   fd  Linux raid autodetect
Partition 1 does not end on cylinder boundary.
/dev/sda2              63         125      499712   fd  Linux raid autodetect
Partition 2 does not end on cylinder boundary.
/dev/sda3             125         653     4242432   fd  Linux raid autodetect
Partition 3 does not end on cylinder boundary.

Disk /dev/sdb: 5368 MB, 5368709120 bytes
255 heads, 63 sectors/track, 652 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/sdb doesn’t contain a valid partition table

Disk /dev/md0: 510 MB, 510590976 bytes
2 heads, 4 sectors/track, 124656 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md0 doesn’t contain a valid partition table

Disk /dev/md1: 511 MB, 511639552 bytes
2 heads, 4 sectors/track, 124912 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md1 doesn’t contain a valid partition table

Disk /dev/md2: 4344 MB, 4344184832 bytes
2 heads, 4 sectors/track, 1060592 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/md2 doesn’t contain a valid partition table
root@server1:~#

Now we copy the partition table of /dev/sda to /dev/sdb:

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

root@server1:~# sfdisk -d /dev/sda | sfdisk –force /dev/sdb
Checking that no-one is using this disk right now …
OK

Disk /dev/sdb: 652 cylinders, 255 heads, 63 sectors/track

sfdisk: ERROR: sector 0 does not have an msdos signature
/dev/sdb: unrecognized partition table type
Old situation:
No partitions found
New situation:
Units = sectors of 512 bytes, counting from 0

Device Boot    Start       End   #sectors  Id  System
/dev/sdb1   *      2048    999423     997376  fd  Linux raid autodetect
/dev/sdb2        999424   1998847     999424  fd  Linux raid autodetect
/dev/sdb3       1998848  10483711    8484864  fd  Linux raid autodetect
/dev/sdb4             0         –          0   0  Empty
Warning: partition 1 does not end at a cylinder boundary
Successfully wrote the new partition table

Re-reading the partition table …

If you created or changed a DOS partition, /dev/foo7, say, then use dd(1)
to zero the first 512 bytes:  dd if=/dev/zero of=/dev/foo7 bs=512 count=1
(See fdisk(8).)
You have new mail in /var/mail/root
root@server1:~#

Afterwards we remove any remains of a previous RAID array from /dev/sdb

mdadm –zero-superblock /dev/sdb1
mdadm –zero-superblock /dev/sdb2
mdadm –zero-superblock /dev/sdb3

… and add /dev/sdb to the RAID array:

mdadm -a /dev/md0 /dev/sdb1
mdadm -a /dev/md1 /dev/sdb2
mdadm -a /dev/md2 /dev/sdb3

Now take a look at

cat /proc/mdstat

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md2 : active raid1 sdb3[2] sda3[0]
4242368 blocks [2/1] [U_]
[===>……………..]  recovery = 16.1% (683520/4242368) finish=0.6min speed=97645K/sec

md1 : active raid1 sdb2[2] sda2[0]
499648 blocks [2/1] [U_]
resync=DELAYED

md0 : active raid1 sdb1[1] sda1[0]
498624 blocks [2/2] [UU]

unused devices: <none>
root@server1:~#

Wait until the synchronization has finished:

root@server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md2 : active raid1 sdb3[1] sda3[0]
4242368 blocks [2/2] [UU]

md1 : active raid1 sdb2[1] sda2[0]
499648 blocks [2/2] [UU]

md0 : active raid1 sdb1[1] sda1[0]
498624 blocks [2/2] [UU]

unused devices: <none>
root@server1:~#

Then install the bootloader on both HDDs:

grub-install /dev/sda
grub-install /dev/sdb

That’s it. You’ve just replaced a failed hard drive in your RAID1 array.

 

  • The Software-RAID Howto: http://tldp.org/HOWTO/Software-RAID-HOWTO.html
  • Ubuntu: http://www.ubuntu.com/

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