Backup and Restore MDADM Raid

Overview

This guide covers backing up and restoring MDADM RAID arrays after an OS reinstall. Planning for the worst, hoping for the best has saved a lot of potentially ruined days. Before any RAID operations, maintain a separate backup copy following the 3-2-1 backup rule.

Backup Process

Step 1: Scan and Save Configuration

Run the mdadm detail scan command:

sudo mdadm --detail --scan

Example output:

ARRAY /dev/md0 metadata=1.2 spares=1 UUID=576d6fe7:c8528a0a:2c0fd278:09a74e22

Save this output to a file for later reference during restoration.

Restoration Process

Step 1: Install mdadm

sudo apt install mdadm

Step 2: Assemble the Array

Add the backed-up scan data to the configuration file, then run:

sudo mdadm --assemble --scan

Step 3: Verify Array Status

sudo mdadm --detail /dev/md0

Check for proper device count, state (should be "clean"), and active devices.

Adding a Spare Drive

If no spare is configured, mark one device as failed, remove it, then re-add as spare:

sudo mdadm --fail /dev/md0 /dev/sdh

sudo mdadm --remove /dev/md0 /dev/sdh

sudo mdadm --add-spare /dev/md0 /dev/sdh

Update the boot configuration:

sudo update-initramfs -u

Mounting the Array

Create Mount Point

sudo mkdir /media/shared

Get UUID

sudo blkid /dev/md0

Example output:

/dev/md0: UUID="b8273bf2-9661-4006-a8d7-19710ead427d" BLOCK_SIZE="4096" TYPE="ext4"

Update fstab

sudo nano /etc/fstab

Add the entry:

UUID=b8273bf2-9661-4006-a8d7-19710ead427d       /media/shared   ext4 defaults,nofail    0       0

Save with Ctrl+X, Y, Enter.

Mount the Array

sudo mount -av

Verify with:

df -h