How To Set Up Software RAID1 On A Running System (Incl. GRUB Configuration) (Debian Lenny)
Version 1.0
Author: Falko Timme 
Follow me on Twitter
This guide explains how to set up software RAID1 on an already running Debian Lenny system. The GRUB 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 Lenny 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, ext3;
- /dev/sda2: swap;
- /dev/sda3: / partition, ext3
In the end I want to have the following situation:
- /dev/md0 (made up of /dev/sda1 and /dev/sdb1): /boot partition, ext3;
- /dev/md1 (made up of /dev/sda2 and /dev/sdb2): swap;
- /dev/md2 (made up of /dev/sda3 and /dev/sdb3): / partition, ext3
This is the current situation:
df -h
server1:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 5.3G 747M 4.3G 15% /
tmpfs 126M 0 126M 0% /lib/init/rw
udev 10M 84K 10M 1% /dev
tmpfs 126M 0 126M 0% /dev/shm
/dev/sda1 228M 29M 188M 14% /boot
server1:~#
fdisk -l
server1:~# fdisk -l
Disk /dev/sda: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000740fc
Device Boot Start End Blocks Id System
/dev/sda1 * 1 30 240943+ 83 Linux
/dev/sda2 31 92 498015 82 Linux swap / Solaris
/dev/sda3 93 783 5550457+ 83 Linux
Disk /dev/sdb: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000
Disk /dev/sdb doesn't contain a valid partition table
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
You will be asked the following question:
MD arrays needed for the root file system: <-- all
Afterwards, we load a few kernel modules (to avoid a reboot):
modprobe md
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:
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
unused devices: <none>
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 /dev/sdb
The output should be as follows:
server1:~# cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
unused devices: <none>
server1:~# sfdisk -d /dev/sda | sfdisk /dev/sdb
Checking that no-one is using this disk right now ...
OK
Disk /dev/sdb: 783 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 * 63 481949 481887 83 Linux
/dev/sdb2 481950 1477979 996030 82 Linux swap / Solaris
/dev/sdb3 1477980 12578894 11100915 83 Linux
/dev/sdb4 0 - 0 0 Empty
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).)
server1:~#
The command
fdisk -l
should now show that both HDDs have the same layout:
server1:~# fdisk -l
Disk /dev/sda: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x000740fc
Device Boot Start End Blocks Id System
/dev/sda1 * 1 30 240943+ 83 Linux
/dev/sda2 31 92 498015 82 Linux swap / Solaris
/dev/sda3 93 783 5550457+ 83 Linux
Disk /dev/sdb: 6442 MB, 6442450944 bytes
255 heads, 63 sectors/track, 783 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/sdb1 * 1 30 240943+ 83 Linux
/dev/sdb2 31 92 498015 82 Linux swap / Solaris
/dev/sdb3 93 783 5550457+ 83 Linux
server1:~#
Next we must change the partition type of our three partitions on /dev/sdb to Linux raid autodetect:
fdisk /dev/sdb
server1:~# fdisk /dev/sdb
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 1e Hidden W95 FAT1 80 Old Minix be Solaris boot
1 FAT12 24 NEC DOS 81 Minix / old Lin bf Solaris
2 XENIX root 39 Plan 9 82 Linux swap / So c1 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 83 Linux c4 DRDOS/sec (FAT-
4 FAT16 <32M 40 Venix 80286 84 OS/2 hidden C: c6 DRDOS/sec (FAT-
5 Extended 41 PPC PReP Boot 85 Linux extended c7 Syrinx
6 FAT16 42 SFS 86 NTFS volume set da Non-FS data
7 HPFS/NTFS 4d QNX4.x 87 NTFS volume set db CP/M / CTOS / .
8 AIX 4e QNX4.x 2nd part 88 Linux plaintext de Dell Utility
9 AIX bootable 4f QNX4.x 3rd part 8e Linux LVM df BootIt
a OS/2 Boot Manag 50 OnTrack DM 93 Amoeba e1 DOS access
b W95 FAT32 51 OnTrack DM6 Aux 94 Amoeba BBT e3 DOS R/O
c W95 FAT32 (LBA) 52 CP/M 9f BSD/OS e4 SpeedStor
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi eb BeOS fs
f W95 Ext'd (LBA) 54 OnTrackDM6 a5 FreeBSD ee EFI GPT
10 OPUS 55 EZ-Drive a6 OpenBSD ef EFI (FAT-12/16/
11 Hidden FAT12 56 Golden Bow a7 NeXTSTEP f0 Linux/PA-RISC b
12 Compaq diagnost 5c Priam Edisk a8 Darwin UFS f1 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor a9 NetBSD f4 SpeedStor
16 Hidden FAT16 63 GNU HURD or Sys ab Darwin boot f2 DOS secondary
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fd Linux raid auto
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fe LANstep
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid ff BBT
1c Hidden W95 FAT3 75 PC/IX
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.
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):
server1:~# mdadm --zero-superblock /dev/sdb1
mdadm: Unrecognised md component device - /dev/sdb1
server1:~#
Otherwise the commands will not display anything at all.
