Mirror is a simple way to gain redundancy on a single Unix server. By building mirrored root disks (as a RAID1 Group), system would be safer in case one disk failed. System still accessible anytime a single disk failure happen.
In this scenario we will try to build a mirrored root disk on Debian Linux server. We will prepare new disk drive as first component of RAID1 group. Then we will copy all content of root disk into it. After data has been copied, we will reboot the server and force the server to boot using the new disk. Once the system up, we will attach existing root disk as second component of RAID1 group. At the end we can use both disk as bootable disk.
We will start create new RAID1 Group for join both disks as mirrored configuration.
- First we will work on the new (
/dev/sdb) or what we called rootmirror. We need to prepare rootmirror before put it in the RAID1 group. Since rootmirror is new disk, it doesn’t have valid partition table yet :
root@debian01:~# fdisk -l /dev/sdb
Disk /dev/sdb: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 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@debian01:~#
What we need to do is copy the partition table from the existing root disk (/dev/sda) using sfdisk command as shown below :
root@debian01:~# sfdisk -d /dev/sda | sfdisk --force /dev/sdb
Checking that no-one is using this disk right now ...
OK
Disk /dev/sdb: 2610 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 194559 192512 83 Linux
/dev/sdb2 194560 19726335 19531776 83 Linux
/dev/sdb3 19726336 23631871 3905536 82 Linux swap / Solaris
/dev/sdb4 23631872 41940991 18309120 83 Linux
Warning: partition 1 does not end at a cylinder boundary
Warning: partition 2 does not start at a cylinder boundary
Warning: partition 2 does not end at a cylinder boundary
Warning: partition 3 does not start at a cylinder boundary
Warning: partition 3 does not end at a cylinder boundary
Warning: partition 4 does not start at a cylinder boundary
Warning: partition 4 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@debian01:~#
After copy the partition table, we can see that rootmirror now has the same partition layout as the root disk :
root@debian01:~# fdisk -l /dev/sdb
Disk /dev/sdb: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 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 * 2048 194559 96256 83 Linux
/dev/sdb2 194560 19726335 9765888 83 Linux
/dev/sdb3 19726336 23631871 1952768 82 Linux swap / Solaris
/dev/sdb4 23631872 41940991 9154560 83 Linux
root@debian01:~#
- Since we will join
rootmirror into a RAID1 group, we need to set every partition under it to use “Linux raid auto” type. We use fdisk command to set the partition type, here is the sample :
root@debian01:~# fdisk /dev/sdb
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 27 Hidden NTFS Win 82 Linux swap / So c1 DRDOS/sec (FAT-
2 XENIX root 39 Plan 9 83 Linux c4 DRDOS/sec (FAT-
3 XENIX usr 3c PartitionMagic 84 OS/2 hidden C: c6 DRDOS/sec (FAT-
4 FAT16 <32M 40 Venix 80286 85 Linux extended c7 Syrinx
5 Extended 41 PPC PReP Boot 86 NTFS volume set da Non-FS data
6 FAT16 42 SFS 87 NTFS volume set db CP/M / CTOS / .
7 HPFS/NTFS/exFAT 4d QNX4.x 88 Linux plaintext de Dell Utility
8 AIX 4e QNX4.x 2nd part 8e Linux LVM df BootIt
9 AIX bootable 4f QNX4.x 3rd part 93 Amoeba e1 DOS access
a OS/2 Boot Manag 50 OnTrack DM 94 Amoeba BBT e3 DOS R/O
b W95 FAT32 51 OnTrack DM6 Aux 9f BSD/OS e4 SpeedStor
c W95 FAT32 (LBA) 52 CP/M a0 IBM Thinkpad hi eb BeOS fs
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a5 FreeBSD ee GPT
f W95 Ext'd (LBA) 54 OnTrackDM6 a6 OpenBSD ef EFI (FAT-12/16/
10 OPUS 55 EZ-Drive a7 NeXTSTEP f0 Linux/PA-RISC b
11 Hidden FAT12 56 Golden Bow a8 Darwin UFS f1 SpeedStor
12 Compaq diagnost 5c Priam Edisk a9 NetBSD f4 SpeedStor
14 Hidden FAT16 <3 61 SpeedStor ab Darwin boot f2 DOS secondary
16 Hidden FAT16 63 GNU HURD or Sys af HFS / HFS+ fb VMware VMFS
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
1c Hidden W95 FAT3 75 PC/IX be Solaris boot ff BBT
1e Hidden W95 FAT1 80 Old Minix
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): 2
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): 3
Hex code (type L to list codes): fd
Changed system type of partition 3 to fd (Linux raid autodetect)
Command (m for help): t
Partition number (1-4): 4
Hex code (type L to list codes): fd
Changed system type of partition 4 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@debian01:~#
Here is the explanation about what happen on the example above :
- Start
fdisk utility by typing “fdisk /dev/sdb” followed by Enter. fdisk utility will ready to work on /dev/sdb.
- Type
t to start setting the partition type. Press Enter to continue.
- Then type the number of partition we want to set. Press Enter to continue.
- There are many partition type available, we can see all available type by type
L followed by Enter.
- In this case we want to use partition type “Linux raid auto” so we type
fd followed by Enter.
- After all partition set up, we must finalize the changes by typing
w (as in “Write this changes to the disk”) followed by Enter.
- With partition type already set, we can continue create
md device a.k.a “virtual partition”. md is abrreviation for Multiple Devices. Before create new md device, we should clean up the partition using the following command :
root@debian01:~# mdadm --zero-superblock /dev/sdb1
root@debian01:~# mdadm --zero-superblock /dev/sdb2
root@debian01:~# mdadm --zero-superblock /dev/sdb3
root@debian01:~# mdadm --zero-superblock /dev/sdb4
Actually this step only applicable if the partition has been used as md device. In this case it didn’t really matter since we use new empty disk.
- To start create
md device, we use mdadm --create command. Here is the syntax to create md device using mdadm command :
mdadm --create /dev/md<ID> --level=<RAID level> --raid-disks=<number of physical disk> <disk#1> <disk#2>
We will create md device for each partition. Since we want to create RAID1 disk group, we set --level=1. And because we only have 2 physical disks involved, then we set --raid-disks=2.
So lets start to prepare first partition on rootmirror as first md device :
root@debian01:~# mdadm --create /dev/md0 --level=1 --raid-disks=2 missing /dev/sdb1
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/md0 started.
root@debian01:~#
Because we don’t want to touch the existing root disk (/dev/sda) yet, we will mark it as “missing”.
Then we can continue with second partition of rootmirror :
root@debian01:~# mdadm --create /dev/md1 --level=1 --raid-disks=2 missing /dev/sdb2
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/md1 started.
root@debian01:~#
Finish by create virtual partition for third and fourth partition of rootmirror :
root@debian01:~# 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@debian01:~#
root@debian01:~# mdadm --create /dev/md3 --level=1 --raid-disks=2 missing /dev/sdb4
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/md3 started.
root@debian01:~#
- Now we have 4 virtual partition, so the next step is to make the new filesystem on each partition. We will use
ext3 filesystem for /dev/md0, /dev/md1, and /dev/md3. To create a ext3 filesystem we use mkfs.ext3 command as shown in the following example :
root@debian01:~# mkfs.ext3 /dev/md0
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
24096 inodes, 96128 blocks
4806 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
12 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
root@debian01:~# mkfs.ext3 /dev/md1
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
610800 inodes, 2439392 blocks
121969 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2499805184
75 block groups
32768 blocks per group, 32768 fragments per group
8144 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
root@debian01:~# mkfs.ext3 /dev/md3
mke2fs 1.42.5 (29-Jul-2012)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
572320 inodes, 2286560 blocks
114328 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2344615936
70 block groups
32768 blocks per group, 32768 fragments per group
8176 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
root@debian01:~#
- For
/dev/md2, we will marked it as swap space using mkswap command as shown in the following example :
root@debian01:~# mkswap -f /dev/md2
Setting up swapspace version 1, size = 1951676 KiB
no label, UUID=2fa8b47b-e889-4160-9fd0-c21b88b6d3e3
root@debian01:~#
- Each virtual partition need to be started during the boot process. So we need to register all the virtual partition we had made into
mdadm.conf file. What we need to register is the output of the following command :
root@debian01:~# mdadm --examine --scan
ARRAY /dev/md/0 metadata=1.2 UUID=5d7d8672:c019a7d0:69310f29:3cd65d04 name=debian01:0
ARRAY /dev/md/1 metadata=1.2 UUID=67631129:b7766c7e:d1200d55:036ad1c6 name=debian01:1
ARRAY /dev/md/2 metadata=1.2 UUID=19cbe54c:2aa2126c:92eda6ee:ffc62fb9 name=debian01:2
ARRAY /dev/md/3 metadata=1.2 UUID=d15793a1:348c6380:a94d73b3:a47f3bf7 name=debian01:3
root@debian01:~#
We can copy those output to /etc/mdadm/mdadm.conf manually using text editor, or we can use simple redirection as shown below :
root@debian01:~# mdadm --examine --scan >> /etc/mdadm/mdadm.conf
- In the Linux system each partition will has its own mountpoint (except for swap partition). Information about the partition and related mountpoint stored inside
/etc/fstab file. Here is the sample of /etc/fstab file :
root@debian01:~# cat /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>
# / was on /dev/sda2 during installation
UUID=4a066d6d-c8ad-46a4-ae54-118da63dcbd2 / ext3 errors=remount-ro 0 1
# /boot was on /dev/sda1 during installation
UUID=1398dd06-7ef2-46c3-9ace-a2328b1db783 /boot ext3 defaults 0 2
# /home was on /dev/sda4 during installation
UUID=8d819942-fe5d-4634-aab7-28ceca9b2fe1 /home ext3 defaults 0 2
# swap was on /dev/sda3 during installation
UUID=c1b679fb-d59f-4478-a138-fe2e3a6bceb0 none swap sw 0 0
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0
root@debian01:~#
Each partition displayed with its UUID (Universally Unique Identifier). Those UUID is belongs to existing root disk (/dev/sda). We need to modify the partition address using new virtual partition identity. Here is the final /etc/fstab after modification :
root@debian01:~# cat /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>
/dev/md1 / ext3 errors=remount-ro 0 1
/dev/md0 /boot ext3 defaults 0 2
/dev/md3 /home ext3 defaults 0 2
/dev/md2 none swap sw 0 0
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0
root@debian01:~#
- Next step is to modify
/etc/default/grub. We need to set GRUB_DISABLE_LINUX_UUID parameter to true. By default GRUB_DISABLE_LINUX_UUID = true was commented, so what we need is to remove # to uncommented that line.
- Before start copying all existing root disk files, we need to mount each virtual partition. Here is the sample how we mount all virtual partitions :
root@debian01:~# mkdir /mnt/md0
root@debian01:~# mkdir /mnt/md1
root@debian01:~# mkdir /mnt/md3
root@debian01:~# mount /dev/md0 /mnt/md0
root@debian01:~# mount /dev/md1 /mnt/md1
root@debian01:~# mount /dev/md3 /mnt/md3
We don’t mount /dev/md2 since it is swap partition.
- With all virtual partition mounted, we can start copy files from existing root disk :
root@debian01:~# cp -dpRx / /mnt/md1
root@debian01:~# cp -dpRx /boot /mnt/md0
root@debian01:~# cp -dpRx /home /mnt/md3
- Then we need to install the boot loader on the virtual partition. We will do it from
chroot environment. There are some steps to prepare chroot environment as shown in the following example :
root@debian01:~# umount /mnt/md0
root@debian01:~# mount /dev/md0 /mnt/md1/boot
root@debian01:~# mount -t proc none /mnt/md1/proc
root@debian01:~# mount -o bind /dev /mnt/md1/dev
root@debian01:~# mount -o bind /sys /mnt/md1/sys
- We can continue to enter
chroot environment & execute update-grub command to fix the boot loader as shown in the following example :
root@debian01:~# chroot /mnt/md1
root@debian01:/# update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-3.2.0-4-686-pae
Found initrd image: /boot/initrd.img-3.2.0-4-686-pae
done
- Still from
chroot environment of virtual partitions, we also need to generate the initramfs image. initramfs is used during boot process to load all root filesystem.
root@debian01:/# update-initramfs -u
update-initramfs: Generating /boot/initrd.img-3.2.0-4-686-pae
mdadm: cannot open /dev/md/0: No such file or directory
mdadm: cannot open /dev/md/1: No such file or directory
mdadm: cannot open /dev/md/2: No such file or directory
mdadm: cannot open /dev/md/3: No such file or directory
root@debian01:/#
We can ignore those kind of errors for now.
- Last things must be done from inside
chroot is reinstall boot loader on both disk drives. Debian system use GRUB boot loader by default. To reinstall boot loader we use grub-install command as shown below :
root@debian01:/# grub-install /dev/sda
Installation finished. No error reported.
root@debian01:/# grub-install /dev/sdb
Installation finished. No error reported.
root@debian01:/# exit
- We can exit
chroot environment and shutdown the system :
root@debian01:/#
exit
root@debian01:~# reboot
root@debian01:~# shutdown -h now
Broadcast message from root@debian7 (pts/3) (Tue Sep 24 01:04:03 2013):
The system is going down for system halt NOW!
root@debian01:~#
- Then we will boot the server using the second disk (
/dev/sdb). If all the setup above success, then system can boot using /dev/sdb (rootmirror) disk.
After reboot system should already use the virtual partition. As we can see from df command output below :
We can check the RAID1 information for each virtual partition using the following command :
- We need to set the partition type on
rootdisk to “Linux raid auto” :
root@debian01:~# fdisk -l /dev/sda
Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0004f798
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 194559 96256 83 Linux
/dev/sda2 194560 19726335 9765888 83 Linux
/dev/sda3 19726336 23631871 1952768 82 Linux swap / Solaris
/dev/sda4 23631872 41940991 9154560 83 Linux
root@debian01:~# fdisk /dev/sda
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): t
Partition number (1-4): 4
Hex code (type L to list codes): fd
Changed system type of partition 4 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@debian01:~#
- We can check that all partition inside
/dev/sda (rootdisk) now has been converted to Linux raid auto type.
root@debian01:~# fdisk -l /dev/sda
Disk /dev/sda: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders, total 41943040 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0004f798
Device Boot Start End Blocks Id System
/dev/sda1 * 2048 194559 96256 fd Linux raid autodetect
/dev/sda2 194560 19726335 9765888 fd Linux raid autodetect
/dev/sda3 19726336 23631871 1952768 fd Linux raid autodetect
/dev/sda4 23631872 41940991 9154560 fd Linux raid autodetect
root@debian01:~#
- Now we can put
rootdisk to the existing RAID1 Group. Each partition under rootdisk will be attached to existing virtual partition (md device).
root@debian01:~# mdadm --add /dev/md0 /dev/sda1
mdadm: added /dev/sda1
root@debian01:~# mdadm --add /dev/md1 /dev/sda2
mdadm: added /dev/sda2
root@debian01:~# mdadm --add /dev/md2 /dev/sda3
mdadm: added /dev/sda3
root@debian01:~# mdadm --add /dev/md3 /dev/sda4
mdadm: added /dev/sda4
root@debian01:~#
- After all partition of
rootdisk join the RAID1 group, system will start recovery/resynchronization automatically. We can monitor the recovery process by looking at /proc/mdstat file :
root@debian01:~# cat /proc/mdstat
Personalities : [raid1]
md3 : active raid1 sda4[2] sdb4[1]
9146240 blocks super 1.2 [2/1] [_U]
resync=DELAYED
md2 : active raid1 sda3[2] sdb3[1]
1951680 blocks super 1.2 [2/1] [_U]
resync=DELAYED
md1 : active raid1 sda2[2] sdb2[1]
9757568 blocks super 1.2 [2/1] [_U]
[==>..................] recovery = 11.6% (1132800/9757568) finish=1.1min speed=125866K/sec
md0 : active raid1 sda1[2] sdb1[1]
96128 blocks super 1.2 [2/2] [UU]
unused devices: <none>
root@debian01:~#
Or we can use mdadm -D command as shown in the following example :
root@debian01:~# mdadm -D /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Tue Sep 24 00:54:31 2013
Raid Level : raid1
Array Size : 96128 (93.89 MiB 98.44 MB)
Used Dev Size : 96128 (93.89 MiB 98.44 MB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:06:30 2013
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : debian01:0 (local to host debian01)
UUID : 5d7d8672:c019a7d0:69310f29:3cd65d04
Events : 55
Number Major Minor RaidDevice State
2 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
root@debian01:~# mdadm -D /dev/md1
/dev/md1:
Version : 1.2
Creation Time : Tue Sep 24 00:54:39 2013
Raid Level : raid1
Array Size : 9757568 (9.31 GiB 9.99 GB)
Used Dev Size : 9757568 (9.31 GiB 9.99 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:06:42 2013
State : clean, degraded, recovering
Active Devices : 1
Working Devices : 2
Failed Devices : 0
Spare Devices : 1
Rebuild Status : 13% complete
Name : debian01:1 (local to host debian01)
UUID : 67631129:b7766c7e:d1200d55:036ad1c6
Events : 138
Number Major Minor RaidDevice State
2 8 2 0 spare rebuilding /dev/sda2
1 8 18 1 active sync /dev/sdb2
root@debian01:~# mdadm -D /dev/md2
/dev/md2:
Version : 1.2
Creation Time : Tue Sep 24 00:54:47 2013
Raid Level : raid1
Array Size : 1951680 (1906.26 MiB 1998.52 MB)
Used Dev Size : 1951680 (1906.26 MiB 1998.52 MB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:06:29 2013
State : clean, degraded, resyncing (DELAYED)
Active Devices : 1
Working Devices : 2
Failed Devices : 0
Spare Devices : 1
Name : debian01:2 (local to host debian01)
UUID : 19cbe54c:2aa2126c:92eda6ee:ffc62fb9
Events : 4
Number Major Minor RaidDevice State
2 8 3 0 spare rebuilding /dev/sda3
1 8 19 1 active sync /dev/sdb3
root@debian01:~# mdadm -D /dev/md3
/dev/md3:
Version : 1.2
Creation Time : Tue Sep 24 00:54:55 2013
Raid Level : raid1
Array Size : 9146240 (8.72 GiB 9.37 GB)
Used Dev Size : 9146240 (8.72 GiB 9.37 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:06:32 2013
State : clean, degraded, resyncing (DELAYED)
Active Devices : 1
Working Devices : 2
Failed Devices : 0
Spare Devices : 1
Name : debian01:3 (local to host debian01)
UUID : d15793a1:348c6380:a94d73b3:a47f3bf7
Events : 18
Number Major Minor RaidDevice State
2 8 4 0 spare rebuilding /dev/sda4
1 8 20 1 active sync /dev/sdb4
root@debian01:~#
- When recovery/resync process completed, both disks will be in sync state. No more
degraded status in the mdadm -D output :
root@debian01:~# mdadm -D /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Tue Sep 24 00:54:31 2013
Raid Level : raid1
Array Size : 96128 (93.89 MiB 98.44 MB)
Used Dev Size : 96128 (93.89 MiB 98.44 MB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:06:43 2013
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : debian01:0 (local to host debian01)
UUID : 5d7d8672:c019a7d0:69310f29:3cd65d04
Events : 55
Number Major Minor RaidDevice State
2 8 1 0 active sync /dev/sda1
1 8 17 1 active sync /dev/sdb1
root@debian01:~# mdadm -D /dev/md1
/dev/md1:
Version : 1.2
Creation Time : Tue Sep 24 00:54:39 2013
Raid Level : raid1
Array Size : 9757568 (9.31 GiB 9.99 GB)
Used Dev Size : 9757568 (9.31 GiB 9.99 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:09:29 2013
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : debian01:1 (local to host debian01)
UUID : 67631129:b7766c7e:d1200d55:036ad1c6
Events : 157
Number Major Minor RaidDevice State
2 8 2 0 active sync /dev/sda2
1 8 18 1 active sync /dev/sdb2
root@debian01:~# mdadm -D /dev/md2
/dev/md2:
Version : 1.2
Creation Time : Tue Sep 24 00:54:47 2013
Raid Level : raid1
Array Size : 1951680 (1906.26 MiB 1998.52 MB)
Used Dev Size : 1951680 (1906.26 MiB 1998.52 MB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:08:59 2013
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : debian01:2 (local to host debian01)
UUID : 19cbe54c:2aa2126c:92eda6ee:ffc62fb9
Events : 23
Number Major Minor RaidDevice State
2 8 3 0 active sync /dev/sda3
1 8 19 1 active sync /dev/sdb3
root@debian01:~# mdadm -D /dev/md3
/dev/md3:
Version : 1.2
Creation Time : Tue Sep 24 00:54:55 2013
Raid Level : raid1
Array Size : 9146240 (8.72 GiB 9.37 GB)
Used Dev Size : 9146240 (8.72 GiB 9.37 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Update Time : Tue Sep 24 01:08:49 2013
State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name : debian01:3 (local to host debian01)
UUID : d15793a1:348c6380:a94d73b3:a47f3bf7
Events : 37
Number Major Minor RaidDevice State
2 8 4 0 active sync /dev/sda4
1 8 20 1 active sync /dev/sdb4
root@debian01:~#
- Now both
/dev/sda & /dev/sdb successfully joined as mirror disks. Both disks will hold the same files. We can verify it by rebooting the server using each disk.
