====== Using mdadm to create a Software RAID in Linux ======

Part of [[engineering:computer_science:linux:linux|Linux]]

===== Installation =====

In Debian:
<code>

sudo apt get install mdadm

</code>

=====   =====

===== Partition Disks for mdadm usage =====

You can use:

<code>
sudo mdadm -E /dev/sd[b-c]

</code>

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

==== Drive Partitioning for RAID: ====

<code>
sudo fdisk /dev/sdX

</code>

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|

=== Useful Options for fdisk ===

^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.

===== Creating a RAID 1 =====
<code>

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

</code>

^Value^Description|
|–create|Create a new RAID|
|/dev/md0|Using /dev/md0|
|–level=mirror|Raid as Mirror|
|–raid-devices=2|Use 2 devices|
|/dev/sd[b-c]1|The devices sdb1 and sdc1|

===== Creating File System on a RAID Device =====

Use mkfs to create a ext4 File System with:
<code>

sudo mkfs.ext4 /dev/md0

</code>
===== Automount RAID on boot =====

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

<code>
sudo nano /etc/fstab

</code>

Eg:

<code>
/dev/md0  /mnt/md0  ext4  defaults,nofail 0 0

</code>

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

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

</code>

Uncomment - if necessary - your array on /etc/mdadm/mdadm.conf by removing the Starting "#":
<code>

sudo nano /etc/mdadm/mdadm.conf

</code>

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

<code>
sudo update-initramfs -u

</code>


===== Check Raid Status =====

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

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

</code>

<code>
sudo mdadm --detail /dev/md0

</code>