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

Version 1.0
Author: Falko Timme

Last edited 05/24/2011

This guide explains how to set up software RAID1 on an already running Debian Squeeze 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 a Debian Squeeze 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  712M  3.1G  19% /
tmpfs                 249M     0  249M   0% /lib/init/rw
udev                  244M  100K  244M   1% /dev
tmpfs                 249M     0  249M   0% /dev/shm
/dev/sda1             472M   25M  423M   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: 0x000b0ecb

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:

apt-get install initramfs-tools mdadm

MD arrays needed for the root file system: <– all

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

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.

How To Set Up Software RAID1 On A Running System (Incl. GRUB2 Configuration) (Debian Squeeze) – Page 2

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

You might see the following message for each command – just press y to continue:

root@server1:~# mdadm –create /dev/md2 –level=1 –raid-disks=2 missing /dev/sdb3
mdadm: Note: this array has metadata at the start and
may not be suitable as a boot device. If you plan to
store ‚/boot‘ on this device please ensure that
your boot-loader understands md/v1.x metadata, or use
–metadata=0.90
Continue creating array? <– y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md2 started.
root@server1:~#

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]
4241396 blocks super 1.2 [2/1] [_U]

md1 : active raid1 sdb2[1]
499700 blocks super 1.2 [2/1] [_U]

md0 : active raid1 sdb1[1]
498676 blocks super 1.2 [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 Tue, 24 May 2011 14:09:09 +0200
# by mkconf 3.1.4-1+8efb9d1
ARRAY /dev/md/0 metadata=1.2 UUID=b40c3165:17089af7:5d5ee79b:8783491b name=server1.example.com:0
ARRAY /dev/md/1 metadata=1.2 UUID=62e4a606:878092a0:212209c5:c91b8fef name=server1.example.com:1
ARRAY /dev/md/2 metadata=1.2 UUID=94e51099:d8475c57:4ff1c60f:9488a09a name=server1.example.com:2

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)
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
/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' 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    defaults        0       0
# / was on /dev/sda3 during installation
#UUID=e4e38871-0115-477d-94f9-34b079d26248 /               ext4    errors=remount-ro 0       1
/dev/md2 /               ext4    errors=remount-ro 0       1
# /boot was on /dev/sda1 during installation
#UUID=7e2fb013-073e-4312-a669-f34b35069bfb /boot           ext4    defaults        0       2
/dev/md0 /boot           ext4    defaults        0       2
# swap was on /dev/sda2 during installation
#UUID=1a5951f8-d0ab-4e0e-b42a-871f81b6fd82 none            swap    sw              0       0
/dev/md1 none            swap    sw              0       0
/dev/scd0       /media/cdrom0   udf,iso9660 user,noauto     0       0
/dev/fd0        /media/floppy0  auto    rw,user,noauto  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
tmpfs /lib/init/rw tmpfs rw,nosuid,mode=0755 0 0
proc /proc proc rw,noexec,nosuid,nodev 0 0
sysfs /sys sysfs rw,noexec,nosuid,nodev 0 0
udev /dev tmpfs rw,mode=0755 0 0
tmpfs /dev/shm tmpfs rw,nosuid,nodev 0 0
devpts /dev/pts devpts rw,noexec,nosuid,gid=5,mode=620 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 'Debian GNU/Linux, with Linux 2.6.32-5-amd64' --class debian --class gnu-linux --class gnu --class os {
        insmod raid
        insmod mdraid
        insmod part_msdos
        insmod ext2
        set root='(md/0)'
        echo    'Loading Linux 2.6.32-5-amd64 ...'
        linux   /vmlinuz-2.6.32-5-amd64 root=/dev/md2 ro  quiet
        echo    'Loading initial ramdisk ...'
        initrd  /initrd.img-2.6.32-5-amd64
}

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='(md/0)‘ – 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.

Because we don’t use UUIDs anymore for our block devices, open /etc/default/grub…

vi /etc/default/grub

… and uncomment the line GRUB_DISABLE_LINUX_UUID=true:

# If you change this file, run 'update-grub' afterwards to update
# /boot/grub/grub.cfg.

GRUB_DEFAULT=0
GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet"
GRUB_CMDLINE_LINUX=""

# Uncomment to enable BadRAM filtering, modify to suit your needs
# This works with Linux (no patch required) and with any kernel that obtains
# the memory map information from GRUB (GNU Mach, kernel of FreeBSD ...)
#GRUB_BADRAM="0x01234567,0xfefefefe,0x89abcdef,0xefefefef"

# Uncomment to disable graphical terminal (grub-pc only)
#GRUB_TERMINAL=console

# The resolution used on graphical terminal
# note that you can use only modes which your graphic card supports via VBE
# you can see them in real GRUB with the command `vbeinfo'
#GRUB_GFXMODE=640x480

# Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to Linux
GRUB_DISABLE_LINUX_UUID=true

# Uncomment to disable generation of recovery mode menu entries
#GRUB_DISABLE_LINUX_RECOVERY="true"

# Uncomment to get a beep at grub start
#GRUB_INIT_TUNE="480 440 1"

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

How To Set Up Software RAID1 On A Running System (Incl. GRUB2 Configuration) (Debian Squeeze) – Page 3

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  714M  3.1G  19% /
tmpfs                 249M     0  249M   0% /lib/init/rw
udev                  244M  132K  244M   1% /dev
tmpfs                 249M     0  249M   0% /dev/shm
/dev/md0              472M   25M  423M   6% /boot
root@server1:~#

The output of

cat /proc/mdstat

should be as follows:

root@server1:~# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb3[1]
4241396 blocks super 1.2 [2/1] [_U]

md1 : active (auto-read-only) raid1 sdb2[1]
499700 blocks super 1.2 [2/1] [_U]

md0 : active raid1 sdb1[1]
498676 blocks super 1.2 [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 : [raid1]
md2 : active raid1 sda3[2] sdb3[1]
4241396 blocks super 1.2 [2/1] [_U]
[==========>……….] recovery = 54.6% (2319808/4241396) finish=0.7min speed=45058K/sec

md1 : active raid1 sda2[2] sdb2[1]
499700 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
498676 blocks super 1.2 [2/2] [UU]

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 : [raid1]
md2 : active raid1 sda3[2] sdb3[1]
4241396 blocks super 1.2 [2/2] [UU]

md1 : active raid1 sda2[2] sdb2[1]
499700 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[2] sdb1[1]
498676 blocks super 1.2 [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 Tue, 24 May 2011 14:09:09 +0200
# by mkconf 3.1.4-1+8efb9d1
ARRAY /dev/md/0 metadata=1.2 UUID=b40c3165:17089af7:5d5ee79b:8783491b name=server1.example.com:0
ARRAY /dev/md/1 metadata=1.2 UUID=62e4a606:878092a0:212209c5:c91b8fef name=server1.example.com:1
ARRAY /dev/md/2 metadata=1.2 UUID=94e51099:d8475c57:4ff1c60f:9488a09a name=server1.example.com:2

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) or (hd1)), that’s why we don’t need /etc/grub.d/09_swraid1_setup anymore.

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

Reboot the system:

reboot

It should boot without problems.

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

How To Set Up Software RAID1 On A Running System (Incl. GRUB2 Configuration) (Debian Squeeze) – Page 4

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 : [raid1]
md2 : active raid1 sda3[2]
4241396 blocks super 1.2 [2/1] [U_]

md1 : active (auto-read-only) raid1 sda2[2]
499700 blocks super 1.2 [2/1] [U_]

md0 : active raid1 sda1[2]
498676 blocks super 1.2 [2/1] [U_]

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

The output of

fdisk -l

should look as follows:

root@server1:~# fdisk -l

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 doesn’t contain a valid partition table

Disk /dev/md0: 510 MB, 510644224 bytes
2 heads, 4 sectors/track, 124669 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, 511692800 bytes
2 heads, 4 sectors/track, 124925 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: 4343 MB, 4343189504 bytes
2 heads, 4 sectors/track, 1060349 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).)
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 : [raid1]
md2 : active raid1 sdb3[3] sda3[2]
4241396 blocks super 1.2 [2/1] [U_]
[======>…………..] recovery = 32.2% (1367168/4241396) finish=1.0min speed=44102K/sec

md1 : active raid1 sdb2[3] sda2[2]
499700 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sdb1[3] sda1[2]
498676 blocks super 1.2 [2/2] [UU]

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

Wait until the synchronization has finished:

root@server1:~# cat /proc/mdstat
Personalities : [raid1]
md2 : active raid1 sdb3[3] sda3[2]
4241396 blocks super 1.2 [2/2] [UU]

md1 : active raid1 sdb2[3] sda2[2]
499700 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sdb1[3] sda1[2]
498676 blocks super 1.2 [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.

10 Links

The Software-RAID Howto: http://tldp.org/HOWTO/Software-RAID-HOWTO.html