Appendix II: 🛠️ Installing Debian on a Software RAID1 Array (with GRUB Redundancy)

This guide walks you through installing Debian onto a RAID1 array using either the Debian Installer or manually with mdadm, and ensures GRUB is installed on both drives—so your system can keep booting even if one disk fails 🚀

✨ Option 1: Using the Debian Installer (Easiest Way)

The Debian Installer includes built-in support for software RAID. Here’s how to do it:

1. Boot the Debian installer

Use a standard Debian ISO. Advanced users may prefer the netinst version.

2. Choose manual partitioning

When prompted, select:

Guided – use entire disk and set up LVM → Manual

3. Prepare RAID partitions

On each disk:

• Create identical partitions (e.g., 500MB EFI, 20GB root, etc.)
• Set partition type to: Use as: physical volume for RAID

4. Create the RAID1 array

Select “Configure software RAID”, then:

• Create new MD device → RAID1
• Select the matching partitions from both disks (e.g., sda1 + sdb1 for /boot)

Repeat this for each volume (e.g., root, swap).

💡 Tip: Avoid placing the EFI partition in RAID—keep EFI on each drive separately.

5. Assign filesystems

Assign your mount points (/, /boot, swap) on the new RAID volumes.

6. Proceed with installation

Continue until Debian is fully installed.

⚙️ Add GRUB to Both Disks (Required for RAID1 Boot Redundancy)

After the system reboots:

1. Open a terminal and run:

   sudo grub-install /dev/sdb
   sudo update-grub

Replace /dev/sdb with the second disk in your array. GRUB was already installed to /dev/sda during install.

🧪 (Optional) Test Your Redundancy

Make sure your system can boot from either disk:

1. Power off.
2. Unplug /dev/sda and boot.
3. Power off, plug /dev/sda back in, unplug /dev/sdb, and boot again.

If both work, your RAID1 boot redundancy is confirmed! 🎉

🧰 Option 2: Manual RAID Setup post-install with mdadm (Advanced Users)

If you're more comfortable configuring RAID after install or using a minimal ISO, here’s how to build your array manually.

1. Install Debian normally (on a single disk or minimal setup)

Boot into your new Debian system.

2. Install mdadm

sudo apt update
sudo apt install mdadm

3. Partition both disks

Use fdisk or parted to create matching partitions on both drives:

sudo fdisk /dev/sda
sudo fdisk /dev/sdb

Set them as type fd (Linux RAID autodetect) or use GPT with parted.

4. Create the RAID array

sudo mdadm --create --verbose /dev/md0 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1

Repeat for additional arrays (e.g., /dev/md1 for root).

5. Format and mount

sudo mkfs.ext4 /dev/md0
sudo mount /dev/md0 /mnt

Install Debian to the mounted RAID device if you're doing a chroot install.

6. Save the RAID config

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

✅ Install GRUB on Both Disks

Regardless of method:

sudo grub-install /dev/sda
sudo grub-install /dev/sdb
sudo update-grub

This ensures either disk can boot independently 🛡️

📝 Summary

Got questions or need help? Reach out to support@ggcircuit.com —we're here to help! 😄

Updated on: 10/12/2025