Adding Live Spare To Raid10 Howto

# Adding Live Spare to RAID10: A How-to Guide

Welcome to this comprehensive guide on adding a live spare to your RAID10 array. This tutorial is intended for experienced sysadmins and DevOps engineers who are self-hosting their infrastructure, automating their workflows, and leveraging open-source tools in their DevOps practices.

Prerequisites

Before diving into the steps, make sure you have the following prerequisites:

1. A working Linux system with MDRAID (Multi-Device RAID Management) installed. The example provided below is based on Ubuntu 20.04 LTS and uses MDADM version 12.6.0. You can install it using the following command:

   sudo apt install mdadm
   

2. A RAID10 array already set up with at least three devices. For this tutorial, let’s assume you have a RAID10 array named md0 comprising of devices /dev/sdc1, /dev/sdd1, and /dev/sde1.

3. Sufficient disk space to accommodate the new device that will become the live spare.

Steps for Adding a Live Spare

1. Identify the New Device

First, identify the new device you wish to add as the live spare. For this example, let’s assume it’s /dev/sdf1. Make sure it’s not currently in use or part of any other RAID array.

2. Initialize the New Device with the Correct RAID Level

Initialize the new device as a member of the existing RAID10 array:

sudo mdadm --create /dev/md127 --verbose \
    --raid-devices=4 \
    --metadata=1.2 \
    --level=10 \
    --chunk=256 \
    /dev/sdc1 \
    /dev/sdd1 \
    /dev/sde1 \
    /dev/sdf1

Explanation:

• /dev/md127 is the name for the new RAID array that will contain the live spare.
• The --raid-devices=4 option specifies that there are 4 devices in total, with the new device being the 4th one.
• The remaining options set up the RAID10 configuration and specify the existing devices in the array.

3. Wait for Sync

After running the command above, the system will start syncing data between the existing devices and the live spare. This process can take some time depending on the amount of data and your hardware’s performance. You can monitor the progress using the following command:

watch -n 10 cat /proc/mdstat

4. Add the New Device to the Existing Array (md0)

Once the new device has been synchronized, you can add it to the existing RAID10 array:

sudo mdadm --manage /dev/md0 --add /dev/md127

5. Verify the Changes

Finally, verify that the new device has been added successfully and is functioning as expected by checking the RAID array status:

sudo mdadm --detail /dev/md0

Troubleshooting

If you encounter issues during this process, consult the MDADM manual or seek assistance from forums such as ServerFault and Stack Overflow.

Conclusion

By following the steps outlined in this guide, you have successfully added a live spare to your RAID10 array. This will provide an extra level of data protection for your critical infrastructure. Remember to regularly monitor your arrays and update your systems to ensure optimal performance and security. Happy DevOps-ing!