This article assumed you have two disks with same storage capacity and only one partition per disk and this one partition occupied the whole disk size. So the operating system detected both disks as sda and sdb. Let's start to partition them first. Note, create partition will make your current data lost and make sure you backup your data somewhere else safely before continue.
root@localhost:~# fdisk /dev/sdb
Welcome to fdisk (util-linux 2.25.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): p
Disk /dev/sdb: 465.8 GiB, 500107862016 bytes, 976773168 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
Disklabel type: dos
Disk identifier: 0x00053dc0
Device Boot Start End Sectors Size Id Type
/dev/sdb1 2048 976773119 976771072 465.8G fd Linux raid autodetect
As you can see above, this is supposed to be the end result it should be. You can type m for help. To create a partition, this is your homework, but as a hints, you need add a new partition, with only 1 partition and used all all the cylinder. Then you need to change the disk partition type to Linux raid auto and remember to save the change you made so fdisk will write the partition and partition type to the disk.
Repeat this procedure for another disk, sdc. The partition information of sdc should be identical to sdb above. Note, you can use fdisk -l /dev/sdb and fdisk -l /dev/sdc to verify the disk is changed accordingly.
root@localhost:~# fdisk /dev/sdc
Welcome to fdisk (util-linux 2.25.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): p
Disk /dev/sdc: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x00019748
Device Boot Start End Sectors Size Id Type
/dev/sdc1 2048 976773119 976771072 465.8G fd Linux raid autodetect
If you do not have mdadm install, you should install it now. To install mdadm, it is as easy as apt-get install mdadm. mdadm is a Linux utility used to manage software RAID devices.
After mdadm is installed, then it is time to add that two partition into mdadm. To do that, issue the following command.
# mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sdb1 /dev/sdc1
The above commend should return immediately and now you can format the new block device using the command.
# mkfs.ext4 /dev/md0
By now, the disk will be formatted to ext4 filesystem and you can check the progress using command cat /proc/mdstat. You can also check the raid detail using this command mdadm --detail /dev/md0 .
root@localhost:~# mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Fri Dec 12 03:54:49 2014
Raid Level : raid1
Array Size : 488254464 (465.64 GiB 499.97 GB)
Used Dev Size : 488254464 (465.64 GiB 499.97 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent
Intent Bitmap : Internal
Update Time : Thu Jan 8 21:42:16 2015
State : active
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0
Name :
UUID : be4c04c4:349da5d9:cbcd7313:7ec7cf60
Events : 26492
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
When the disk is done formatted, you should be able to see output like the following.
root@localhost:~# cat /proc/mdstat
Personalities : [raid1] [linear] [multipath] [raid0] [raid6] [raid5] [raid4] [raid10]
md0 : active raid1 sdc1[1] sdb1[0]
488254464 blocks super 1.2 [2/2] [UU]
bitmap: 4/4 pages [16KB], 65536KB chunk
unused devices: <none>
Note the UU, if the raid is degraded, like a disk failure, you should be able to see [_U] or [U_] depending on which disk is failing.
The last step is to mount this new device to a mount point so that we can start to use. The example below create a mount point on /mnt/myBackup and mount md0 to /mnt/myBackup
root@localhost:~# mkdir /mnt/myBackup
root@localhost:~# mount /dev/md0 /mnt/myBackup
To make this change survive over a reboot, you should add an entry into /etc/fstab.
/dev/md0 /mnt/myBackup ext4 defaults 1 2
You should also save the raid configuration into mdadm configuration file. The following command does just that.
root@localhost:~# mdadm --detail --scan > /etc/mdadm/mdadm.conf
That's it, I hope your data are save from now on.
