Here is an example of migrating a running Ubuntu system to a software RAID1.
In the process, you will need to perform two reboots.
The first step is to switch to the root user if not yet:
sudo -i
Let’s see a list of disks and partitions:
fdisk -l fdisk -l | grep '/dev/sd' lsblk -o NAME,UUID
Suppose that the system uses one disk, for example /dev/sda and has one main partition, /dev/sda1.
For the test, I installed a clean Ubuntu Server 18.04, the disk was parted by default, swap was the file on the same partition.
To create a raid, we connect another disk of the same size, it will be called /dev/sdb.
Install mdadm and necessary utilities (they are usually installed by default):
apt-get install initramfs-tools mdadm
In order to make sure that all necessary modules and components are installed, execute the following command:
cat /proc/mdstat
If the necessary modules are not loaded, then load them:
modprobe linear modprobe multipath modprobe raid1
Let’s divide the new disk /dev/sdb in the same way as:
sfdisk -d /dev/sda | sfdisk --force /dev/sdb
Let’s check:
fdisk -l
In the next step, change the partition type of the new hard disk /dev/sdb to “Linux raid autodetect” (since partition 1, then after “t” it will not be asked to specify the partition number):
fdisk /dev/sdb t fd w
Make sure that the partition type /dev/sdb is Linux raid autodetect:
fdisk -l
Create an array md0 using the missing:
mdadm --create /dev/md0 --level=1 --metadata=1.0 --raid-disks=2 missing /dev/sdb1
Let’s check:
cat /proc/mdstat
If something does not work, then you can remove the raid and try again:
mdadm --stop /dev/md0
Let’s specify the file system of the array:
mkfs.ext4 /dev/md0
Let’s make a backup copy of the configuration file mdadm and add information about the new array:
cp /etc/mdadm/mdadm.conf /etc/mdadm/mdadm_backup.conf mdadm --examine --scan >> /etc/mdadm/mdadm.conf
Mount /dev/md0 into the system:
mkdir /mnt/md0 mount /dev/md0 /mnt/md0 mount
At me it was displayed at the bottom of the list:
/dev/md0 on /mnt/md0 type ext4 (rw,relatime,data=ordered)
In the /etc/fstab file comment the lines about /dev/sda and add about the array:
nano /etc/fstab /dev/md0 / ext4 errors=remount-ro 0 1
Let’s see the file /etc/mtab whether there is a record about the raid:
cat /etc/mtab
Let’s look at the exact names of the files /vmlinuz, /initrd.img:
ls /
Create a file from the GRUB2 boot menu and open it in the editor:
cp /etc/grub.d/40_custom /etc/grub.d/09_raid1_test nano /etc/grub.d/09_raid1_test
Add the contents (instead of /vmlinuz and /initrd.img, we’ll specify the correct names if they are different):
#!/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' --class debian --class gnu-linux --class gnu --class os {
insmod mdraid1x
insmod part_msdos
insmod ext2
set root='(md/0)'
echo 'Loading Linux'
linux /vmlinuz root=/dev/md0 ro quiet
echo 'Loading initial ramdisk ...'
initrd /initrd.img
}
Open the file /etc/default/grub in the text editor:
nano /etc/default/grub
Uncomment a couple of lines:
GRUB_TERMINAL=console GRUB_DISABLE_LINUX_UUID=true
Update the loader:
update-grub
Prepare ramdisk:
update-initramfs -u
Install the bootloader on both disks:
grub-install /dev/sda grub-install /dev/sdb
Copy all the data to the previously mounted md0 array:
cp -dpRx / /mnt/md0
Restart the system:
reboot
When the system starts, in the boot menu it will be the first menu /etc/grub.d/09_raid1_test, if there are problems with the download, you can choose to boot from /dev/sda.
Make sure that the system is started with /dev/md0:
df -h
Again, switch to the root user if not under it:
sudo -i
Change the partition type of the old hard disk:
fdisk /dev/sda t fd w
Let’s check:
fdisk -l
Add to the array the old disk:
mdadm --add /dev/md0 /dev/sda1
Wait until the synchronization is completed and make sure that the raid is in order – UU:
cat /proc/mdstat
Update the array information in the mdadm configuration file:
cp /etc/mdadm/mdadm_backup.conf /etc/mdadm/mdadm.conf mdadm --examine --scan >> /etc/mdadm/mdadm.conf
Remove our temporary GRUB menu, it’s no longer necessary:
rm -f /etc/grub.d/09_raid1_test
Update and install GRUB again:
update-grub update-initramfs -u grub-install /dev/sda grub-install /dev/sdb
Restart the system to make sure it runs successfully:
reboot
At this, the migration of the running Ubuntu system to the software RAID1 is complete.
If one of the disks, /dev/sda or /dev/sdb stops working, the system will run and boot.
For stability, you can add more disks of the same size to the array.
See also my articles:
mdadm – utility for managing software RAID arrays
How to create SWAP in Linux
Managing disk partitions in Ubuntu using fdisk
Loading and Unloading Modules in Linux