Using mdadm to create a Software RAID in Linux

Part of Linux

In Debian:

sudo apt get install mdadm

You can use:

sudo mdadm -E /dev/sd[b-c]

to check if the devices are part of a RAID / super-block is found.

sudo fdisk /dev/sdX

To create the partition, input the following values in order. Each Input should be followed by a confirmation (ENTER)

Value	Description
n	New primary Partition
P	Define as Primary Partition
1	Partition Number
(ENTER)	Confirm Default Starting Block
(ENTER)	Confirm Default End Block
t	Choose partitions type
fd	Partition type: Linux Raid auto
w	Write Changes

Value	Description
d	Delete selected partition
p	Print partitions information
L	List available types of partitions

Don't forget to repeat the steps for all disks you using on the RAID.

sudo mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sd[b-c]1

Use mkfs to create a ext4 File System with:

sudo mkfs.ext4 /dev/md0

Edit your fstab to auto-mount your RAID on boot:

sudo nano /etc/fstab

Eg:

/dev/md0  /mnt/md0  ext4  defaults,nofail 0 0

To make sure that the array is reassembled automatically at boot, adjust your /etc/mdadm/mdadm.conf:

sudo mdadm --detail --scan | sudo tee -a /etc/mdadm/mdadm.conf

Uncomment - if necessary - your array on /etc/mdadm/mdadm.conf by removing the Starting “#”:

sudo nano /etc/mdadm/mdadm.conf

Update the initramfs again so that the early boot process does not try to bring an unavailable array online:

sudo update-initramfs -u

You can use the following commands to check the status of your RAID:

sudo mdadm -E /dev/sd[b-c]1

sudo mdadm --detail /dev/md0

Installation