How to Set Up RAID on Arch Linux

RAID (Redundant Array of Independent Disks) is a powerful method to combine multiple physical drives into a single logical unit to improve performance, provide redundancy, or both. Whether you’re aiming for fault tolerance or better throughput, Arch Linux—being a do-it-yourself distribution—offers the flexibility to set up and manage RAID arrays according to your needs.

In this article, we’ll walk through the steps of setting up software RAID using mdadm on Arch Linux. We’ll cover the common RAID levels, installation of necessary tools, RAID creation, configuration for auto-assembly at boot, and array monitoring.

🔧 Prerequisites

Before proceeding, ensure the following:

• You have at least two unused storage devices (disks or partitions).
• You are comfortable working in the terminal.
• You have root access or are using a user with sudo privileges.
• A fresh Arch Linux installation or a non-critical system is recommended for learning and testing.

Important: Back up all important data before modifying disk partitions.

🔍 Understanding RAID Levels

Arch Linux supports various RAID levels via software using mdadm. Here are the most common ones:

• RAID 0 (Striping): Improved performance, no redundancy. Requires at least 2 disks.
• RAID 1 (Mirroring): Redundancy by duplicating data. Requires at least 2 disks.
• RAID 5 (Striped with Parity): Balanced performance and redundancy. Requires at least 3 disks.
• RAID 6 (Double Parity): Like RAID 5 but with extra fault tolerance. Requires at least 4 disks.
• RAID 10 (1+0): Combination of RAID 1 and RAID 0. Requires at least 4 disks.

In this guide, we’ll demonstrate setting up RAID 1, but the steps are similar for other RAID levels.

🛠 Step 1: Install Required Packages

Arch Linux does not include RAID tools by default. You’ll need to install the mdadm package:

sudo pacman -Syu mdadm

💽 Step 2: Identify the Disks

You need to identify the devices you want to use for the RAID array. You can use lsblk or fdisk:

lsblk

For example, assume you plan to use /dev/sdb and /dev/sdc for your RAID array.

If the disks contain any existing partitions or filesystems, wipe them:

sudo wipefs -a /dev/sdb
sudo wipefs -a /dev/sdc

Optionally, zero the superblocks to avoid RAID conflicts:

sudo mdadm --zero-superblock /dev/sdb
sudo mdadm --zero-superblock /dev/sdc

🧱 Step 3: Create the RAID Array

To create a RAID 1 array:

sudo mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sdb /dev/sdc

Explanation:

• /dev/md0: The new RAID device.
• --level=1: RAID 1.
• --raid-devices=2: Number of devices in the array.
• /dev/sdb /dev/sdc: Devices to include.

You can monitor the build process using:

cat /proc/mdstat

You should see the synchronization progress. Depending on disk size, this may take some time.

🧾 Step 4: Save the RAID Configuration

To ensure the array is recognized on boot, save its configuration:

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

If the file doesn’t exist, create it:

sudo mdadm --detail --scan > /etc/mdadm.conf

🧰 Step 5: Create a Filesystem

Once the array is built, format it with a filesystem of your choice, for example ext4:

sudo mkfs.ext4 /dev/md0

Then create a mount point and mount the array:

sudo mkdir -p /mnt/raid
sudo mount /dev/md0 /mnt/raid

Verify with:

df -h

🧷 Step 6: Configure Auto-Mount at Boot

Get the UUID of the RAID device:

sudo blkid /dev/md0

Sample output:

/dev/md0: UUID="12345678-1234-5678-1234-567812345678" TYPE="ext4"

Now edit /etc/fstab to mount the RAID array at boot:

sudo nano /etc/fstab

Add the following line (replace UUID with the one from your output):

UUID=12345678-1234-5678-1234-567812345678 /mnt/raid ext4 defaults 0 2

Save and exit.

🔄 Step 7: Reboot and Verify

Reboot your system to ensure everything is correctly assembled and mounted:

sudo reboot

After booting, check:

lsblk
cat /proc/mdstat
mount | grep /mnt/raid

🧪 Optional: Simulate Disk Failure

To test RAID 1 redundancy, simulate a failure:

sudo mdadm --fail /dev/md0 /dev/sdb
sudo mdadm --remove /dev/md0 /dev/sdb

You can then add a new disk (e.g., /dev/sdd) to rebuild the array:

sudo mdadm --add /dev/md0 /dev/sdd

Monitor the rebuild process:

watch cat /proc/mdstat

🛡 Monitoring RAID Health

RAID should be monitored regularly. Here are a few tools and tips:

1. Use mdadm for status checks

sudo mdadm --detail /dev/md0

2. Set up email alerts

Install a mail system like msmtp or mailx, then edit /etc/mdadm.conf:

MAILADDR yourname@example.com

Enable monitoring via a cron job or systemd timer.

🧹 Cleaning Up (Optional)

To dismantle a RAID array:

1. Unmount the array:

   sudo umount /mnt/raid
   

2. Stop the array:

   sudo mdadm --stop /dev/md0
   

3. Zero the superblocks:

   sudo mdadm --zero-superblock /dev/sdb
   sudo mdadm --zero-superblock /dev/sdc
   

4. Optionally remove /etc/mdadm.conf entries and update /etc/fstab.

🔚 Conclusion

Setting up RAID on Arch Linux gives you full control over redundancy, performance, and flexibility for various storage scenarios. Whether you’re building a home NAS, media server, or just want to experiment with fault tolerance, RAID is a valuable tool in your sysadmin toolkit.

Key takeaways:

• Use RAID 0 for performance, RAID 1 for redundancy, and RAID 5/6/10 for more advanced setups.
• mdadm provides powerful, flexible software RAID tools.
• Always monitor RAID arrays and configure alerts for disk failures.
• RAID is not a substitute for backups—always back up critical data externally.

By following this guide, you should now have a functioning RAID array on Arch Linux ready for your storage needs.