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

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Submitted by falko (Contact Author) (Forums) on Sun, 2010-07-04 19:01. :: Ubuntu | Storage

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

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
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Last edited 06/21/2010

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.


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Comments will be published after administrator approval.
Submitted by HST (not registered) on Sat, 2013-10-19 14:08.
This was a great help to me in a slightly harder (?) problem, namely moving to RAID10 from RAID1 with only two disks.  I had to make a few appropriate minor changes for Debian, for raid10 and for an existing RAID in place.

Details on request.

Submitted by Hans (not registered) on Wed, 2013-02-27 23:34.

Thank you for this excellent Tutorial!

Still, grub2 comes with surprises. When /dev/sda fails it might happen that the system runs into an endless loop of boot trials (not even showing the grub menu) because grub won't be able to find the files needed. I could solve the problem with 

grub-install --modules="raid" /dev/sdx
See http://ubuntuforums.org/showthread.php?p=12534060#post12534060:

1. Install grub on EACH of the array's disks and pass grub-install the option flag --modules="raid". Without --modules="raid" it will fail.
2. Rebuild your initramfs.

Submitted by Bill (not registered) on Sun, 2012-09-02 06:56.
asus-bill / # gfdisk -G
asus-bill / # sfdisk -d /dev/sda | sfdisk --force /dev/sdb
Checking that no-one is using this disk right now ...

WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util sfdisk doesn't support GPT. Use GNU Parted.

OK

Disk /dev/sdb: 121601 cylinders, 255 heads, 63 sectors/track
Old situation:
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

   Device Boot Start     End   #cyls    #blocks   Id  System
/dev/sdb1          0+ 121601- 121602- 976762583+  ee  GPT
/dev/sdb2          0       -       0          0    0  Empty
/dev/sdb3          0       -       0          0    0  Empty
/dev/sdb4          0       -       0          0    0  Empty
New situation:
Units = sectors of 512 bytes, counting from 0

   Device Boot    Start       End   #sectors  Id  System
/dev/sdb1             1 1953525167 1953525167  ee  GPT
/dev/sdb2             0         -          0   0  Empty
/dev/sdb3             0         -          0   0  Empty
/dev/sdb4             0         -          0   0  Empty
Warning: partition 1 does not end at a cylinder boundary
Warning: no primary partition is marked bootable (active)
This does not matter for LILO, but the DOS MBR will not boot this disk.
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).)
asus-bill / # gfdisk -l

Disk /dev/sda: 1000 GB, 1000202273280 bytes
255 heads, 63 sectors/track, 121601 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System 
/dev/sda1               1        2835    22772106   83  Linux 
Warning: Partition 1 does not end on cylinder boundary.
/dev/sda2            2835      121601   953987895   83  Linux 
Warning: Partition 2 does not end on cylinder boundary.
Error: /dev/sdb: unrecognised disk label
asus-bill / # 
 
Ok, doesn't work with GPT drive? (sdb in this scenario is an unallocated, new drive straight out of the box, Seagate Barracuda 1TB 64mb cache, identical to sda)