Reset Existing RAID 0 & Create RAID 10 Array with mdadm on RHEL9

Source: Dev.to

Introduction

Linux’s software RAID can be managed with the mdadm utility. This guide shows how to:

1. Reset an existing RAID 0 array on a RHEL 9 system.
2. Create a new RAID 10 array using four devices.

You need SSH access to the RHEL 9 server with root or sudo privileges and the required storage devices (2 + for RAID 0, 4 for RAID 10).

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Resetting an Existing RAID 0 Array

1. Identify the active array

cat /proc/mdstat

Sample output

Personalities : [raid0]
md0 : active raid0 sdc[1] sdb[0]
      10475520 blocks super 1.2 512k chunks

unused devices: 

2. Unmount the filesystem

umount /dev/md0

3. Stop and remove the array

mdadm --stop /dev/md0

4. Locate the component devices

lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT

Sample output

NAME               SIZE FSTYPE            TYPE MOUNTPOINT
sda                 50G                   disk
├─sda1               1G xfs               part /boot
├─sda2             600M vfat              part /boot/efi
└─sda3            48.4G LVM2_member       part
  └─rootVG-rootLV    4G xfs               lvm  /
sdb                  5G linux_raid_member disk
sdc                  5G linux_raid_member disk

5. Zero the superblocks

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

6. Clean configuration files

Remove or comment any RAID‑related entries in:

• /etc/fstab
• /etc/mdadm/mdadm.conf

7. Rebuild the initramfs

dracut -f

Reboot the server (optional) before creating a new array.

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Building a RAID 10 Array

1. Verify the devices to be used

lsblk -o NAME,SIZE,FSTYPE,TYPE,MOUNTPOINT

Sample output

NAME               SIZE FSTYPE      TYPE MOUNTPOINT
sda                 50G             disk
├─sda1               1G xfs         part /boot
├─sda2             600M vfat        part /boot/efi
└─sda3            48.4G LVM2_member part
  └─rootVG-rootLV    4G xfs         lvm  /
sdb                  5G             disk
sdc                  5G             disk
sdd                  5G             disk
sde                  5G             disk

2. Create the RAID 10 array

Note: Omitting --layout defaults to the near layout.

mdadm --create --verbose /dev/md0 \
      --level=10 \
      --raid-devices=4 \
      /dev/sdb /dev/sdc /dev/sdd /dev/sde

Sample interaction

To optimalize recovery speed, it is recommended to enable write‑intent bitmap, do you want to enable it now? [y/N]? y
mdadm: chunk size defaults to 512K
mdadm: size set to 5237760K
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.

3. Verify the new array

cat /proc/mdstat

Sample output

Personalities : [raid4] [raid5] [raid6] [raid10]
md0 : active raid10 sde[3] sdd[2] sdc[1] sdb[0]
      6983680 blocks super 1.2 512K chunks 3 offset-copies [4/4] [UUUU]
      [===>.................]  resync = 18.2% (1271808/6983680) finish=0.8min speed=115618K/sec
      bitmap: 1/1 pages [4KB], 65536KB chunk

unused devices: 

4. Create a filesystem

mkfs.xfs /dev/md0

5. Mount the filesystem

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

6. Verify the mount

df -h

Sample output

Filesystem                 Size  Used Avail Use% Mounted on
/dev/md0                   6.6G   80M  6.6G   2% /mnt/md0
...

7. Enable automatic assembly at boot

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

8. Add the mount point to /etc/fstab

echo '/dev/md0 /mnt/md0 xfs defaults,nofail,discard 0 0' | sudo tee -a /etc/fstab

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Completion

The RAID 10 array is now built, formatted, and configured to assemble and mount automatically on subsequent reboots. Reboot the server and confirm the array’s status with cat /proc/mdstat and df -h.