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Recovers all types of corrupted RAID arrays
Recovers all types of corrupted RAID arrays
Last updated: Mar 27, 2024

How to Recover Data from RAID 5 on MDADM (ubuntu)

Recovering data from a RAID 5 array can be a daunting task, especially when dealing with the complexity and intricacies of Linux's mdadm tool. This article aims to demystify the process, providing a clear, step-by-step guide to help you retrieve your precious data from a RAID 5 setup using mdadm on Linux.

We will begin by understanding the fundamentals of RAID 5 technology, highlighting its benefits for data redundancy and performance, and explaining why it is a popular choice for data storage. Next, we will delve into the specifics of the mdadm tool, a powerful utility for managing software RAID arrays in Linux environments, outlining its key features and capabilities.

The core of this article will focus on the recovery process itself. We will guide you through the initial steps of diagnosing the problem, identifying the failed components, and preparing for the recovery operation. Following that, we will provide detailed instructions on how to use mdadm to reconstruct the RAID array and recover the data, including tips on handling potential pitfalls and ensuring the best possible outcome.

What is RAID 5 system?

A RAID 5 system is a type of Redundant Array of Independent Disks (RAID) configuration that combines three or more hard drives to offer a balance of improved data performance and data redundancy. It employs block-level striping with distributed parity, which means that data and parity (used for reconstruction in case of a drive failure) are spread across all the drives in the array.

In a RAID 5 setup, the total storage capacity is the sum of the capacities of all the drives minus the capacity of one drive. This is because RAID 5 uses one drive's worth of space to store parity information, which is essential for data recovery in the event of a single drive failure. For instance, in a setup with three 1TB drives, the total available storage would be 2TB, with 1TB used for parity.

Key features of RAID 5 include:

  • Data Redundancy and Fault Tolerance: RAID 5 can withstand the failure of one drive without losing data or access to data. If a drive fails, the data it contained can be reconstructed from the remaining drives' data and parity information.
  • Improved Performance: By striping data across multiple drives, RAID 5 offers improved read performance compared to a single drive. Write performance is somewhat reduced due to the overhead of calculating and writing parity information.
  • Efficient Use of Storage: RAID 5 provides a good balance between storage efficiency and redundancy. Only one drive's worth of space is sacrificed for parity, unlike RAID 1, which requires doubling the number of drives for mirroring.
  • Hot-Swap Capability: Many RAID 5 systems allow for hot-swapping, where a failed drive can be replaced without shutting down the system. The RAID controller will rebuild the data on the new drive using the existing array's data and parity.

It is essential to note that RAID 5 is not a substitute for regular backups. While it provides redundancy to safeguard against hardware failure, it does not protect against data corruption, user errors, or catastrophic events that could affect all drives simultaneously. RAID 5 is best used as part of a comprehensive data protection strategy that includes regular backups and, if necessary, additional layers of redundancy.

What Is mdadm?

mdadm stands for "multiple device administrator" and is a utility for managing and monitoring software RAID devices in Linux. It provides a powerful set of command-line tools to create, manage, troubleshoot, and monitor RAID arrays and their components. mdadm supports various RAID levels, including RAID 0 (stripe), RAID 1 (mirror), RAID 5, RAID 6, and nested arrays like RAID 10 (1+0).

Here are some key features and functionalities of mdadm:

  • Array Creation:mdadm can combine multiple physical disks into a single logical RAID array. It supports the creation of different RAID levels, each offering distinct benefits in terms of redundancy, performance, and storage efficiency.
  • Array Management: Users can manage array membership, replace failed drives, and control various parameters of the RAID array, such as the rebuild speed or the read/write policy.
  • Monitoring:mdadm provides monitoring capabilities that can alert administrators to failures or problems with RAID arrays. It can monitor the health of the drives and the integrity of the data, sending notifications if issues are detected.
  • Array Assembly:mdadm can assemble an array at boot time or after a system failure, ensuring that the data remains accessible as long as the necessary drives are functioning.
  • Resizing Arrays:mdadm allows for the resizing of RAID arrays and the addition of new drives to an existing array, offering flexibility as storage needs grow.
  • Fault Recovery: In the event of a drive failure in a redundant array (such as RAID 1, 5, or 6), mdadm can be used to remove the failed drive and add a replacement, initiating the rebuild process to restore redundancy.

mdadm is widely used in Linux environments for managing software RAID configurations, providing a versatile and reliable toolset for both simple and complex storage setups. It's particularly useful for system administrators and power users who require direct control over RAID storage management without relying on hardware RAID controllers.

RAID is not a backup!

Limitations of mdadm

While mdadm is a powerful tool for managing software RAID configurations in Linux, it has some limitations that users should be aware of:

  • Performance Overhead: Since mdadm operates as a software RAID solution, it utilizes the system's CPU for RAID operations such as parity calculations (in RAID 5 or 6) and data distribution. This can lead to increased CPU utilization compared to hardware RAID solutions, which use dedicated processors on the RAID card.
  • Dependent on System Resources: The performance and reliability of arrays managed by mdadm are tied to the overall stability and performance of the system. Any issues affecting the host system, such as high CPU load, memory pressure, or an unstable operating system, can impact the RAID performance and reliability.
  • No Hardware RAID Features:mdadm lacks some advanced features found in hardware RAID controllers, like battery-backed cache, which can protect data integrity during unexpected power outages and improve write performance.
  • Complexity: While mdadm offers robust features and flexibility, it can be complex to set up and manage, especially for users who are not familiar with Linux command-line interfaces or RAID concepts. Understanding mdadm's various options and configurations requires a learning curve.
  • Recovery Limitations: In case of multiple simultaneous drive failures, especially in RAID 5, data recovery can be impossible since RAID 5 can only withstand a single drive failure. Users must be vigilant about monitoring and replacing failed drives promptly to avoid data loss.
  • Boot Issues: Depending on the setup, especially when using RAID for boot volumes, users may face complexities during system boot-up or need to perform additional configurations to ensure the boot loader can recognize and use the RAID array.
  • Software Updates and Compatibility: As with any software tool, there is a dependency on keeping mdadm updated for security and functionality. There can be compatibility issues with different kernel versions or distributions, necessitating careful management and testing during upgrades.

While these limitations are significant, mdadm remains a popular and effective tool for managing RAID arrays in Linux environments, particularly for those who prefer software RAID's flexibility and cost-effectiveness over hardware RAID solutions. Users must weigh these limitations against their specific needs and the environment in which they are operating.

Tips Before RAID Recovery Using mdadm

Before attempting RAID recovery using mdadm, it's crucial to prepare adequately to maximize the chances of a successful recovery and minimize the risk of data loss. Here are some essential tips to consider:

  • Backup Data: If possible, create a complete backup of all data on the RAID array and any other important data on the system. Recovery processes can sometimes lead to unexpected outcomes, and having a backup ensures that you don't lose valuable data.
  • Assess the Situation: Understand the nature of the problem. Identify which drives are failing or have failed and determine the status of the RAID array. Avoid writing any new data to the array, as this can overwrite lost data or exacerbate issues.
  • Use Read-Only Mode: If you're investigating a degraded array or attempting to recover RAID data, mount the filesystem in read-only mode to prevent any write operations that could alter the data.
  • Check Array Status: Use mdadm to examine the status of the RAID array. The mdadm --detail /dev/mdX command can provide valuable insights into which disks are active, faulty, or missing.
  • Prepare a Safe Environment: Consider performing recovery operations on a clone or an image of the affected drives, especially if the data is critical. This approach ensures that the original data remains unaltered and accessible in case the recovery needs to be attempted again.
  • Gather Necessary Tools: Ensure you have all the necessary tools and resources available. In addition to mdadm, you might need data recovery software, spare drives for cloning, and enough storage space for recovered data.
  • Avoid Reinitializing: Do not reinitialize or recreate the RAID array without ensuring that you have a complete backup or image of the existing array. Reinitializing can lead to permanent data loss.
  • Document the Process: Keep detailed notes of all steps taken during the recovery process, including commands executed, observations, and any errors encountered. This documentation can be invaluable for troubleshooting or if you need to seek help from a professional.
  • Seek Professional Help if Unsure: If the data is extremely valuable or the RAID configuration is complex, consider seeking assistance from data recovery professionals. They have the experience and tools to maximize recovery success rates.
  • Stay Patient and Methodical: RAID recovery can be a time-consuming and intricate process. Rushing through the steps or taking shortcuts can jeopardize your data. Stay patient, follow each step carefully, and do not perform any action unless you're confident of its implications.

By following these tips, you can approach RAID recovery using mdadm with a well-prepared strategy, enhancing your chances of successfully retrieving your data while minimizing risks.

How To Recover RAID 5 Using mdadm?

Recovering a RAID 5 array using mdadm requires careful planning and execution to avoid data loss. Here's a step-by-step guide to help you through the process:

1. Diagnose the Problem

First, identify the issue with the RAID array. Check the status of the RAID array and individual disks:

cat /proc/mdstat mdadm --detail /dev/mdX

Replace /dev/mdX with your RAID device. This will help you understand which drive(s) have failed.

2. Stop the RAID Array

If the array is still active, you need to stop it safely without causing data corruption:

mdadm --stop /dev/mdX

3. Remove the Failed Drive

Physically remove the failed drive from the system. Ensure that you identify the correct drive to avoid removing a working drive.

4. Replace the Failed Drive

Insert a new drive that is of equal or larger capacity compared to the old one. It's crucial that the new drive can integrate seamlessly into the array.

5. Partition the New Drive

Make sure the new drive has the same partition structure as the other drives in the array. You can use tools like fdisk or gdisk for partitioning:

sfdisk -d /dev/sdY | sfdisk /dev/sdZ

Replace /dev/sdY with a working drive from the array and /dev/sdZ with the new drive.

6. Add the New Drive to the Array

Now, you need to add the new drive to the array and start the rebuilding process:

mdadm --add /dev/mdX /dev/sdZ1

Again, replace /dev/mdX with your RAID device and /dev/sdZ1 with the new partition.

7. Monitor the Rebuild Process

The array will begin to rebuild using the new drive. This process can take a long time, depending on the size of the drives and the speed of your system. You can monitor the progress with:

cat /proc/mdstat mdadm --detail /dev/mdX

8. Verify the Array Status

Once the rebuild is complete, verify the status of the RAID array to ensure that it is active and not in a degraded or faulty state:

mdadm --detail /dev/mdX

9. Test and Validate

Before putting the array back into production use, perform thorough testing to validate the integrity of the data and the functionality of the RAID array.


  • Always have a complete backup of your data before attempting recovery procedures.
  • If you're unsure at any stage, it's best to consult with a data recovery specialist to avoid risking data loss.
  • The steps above assume a single drive failure. If multiple drives fail in a RAID 5 setup, the array cannot be rebuilt, and you would need to resort to data recovery services.

By following these steps, you can successfully recover a RAID 5 array using mdadm. Remember, the key to successful data recovery is to proceed cautiously, understanding each step and its implications.


In conclusion, understanding and managing RAID 5 arrays using mdadm on Linux can significantly enhance data redundancy and performance while providing a cost-effective solution for data storage. While RAID 5 offers a balance between storage efficiency, performance, and fault tolerance, it is essential to recognize its limitations, particularly regarding performance overhead and recovery limitations.

Before attempting any RAID recovery process, it is crucial to take precautionary steps such as backing up data, understanding the problem, and ensuring you have the right tools and environment for recovery. The process of recovering a RAID 5 array using mdadm involves diagnosing the issue, safely stopping the array, replacing the failed drive, and carefully rebuilding the array, all while monitoring the process closely.

It's worth emphasizing that RAID technology, including RAID 5, is not a substitute for regular backups. It is designed to provide fault tolerance against hardware failure but does not protect against data corruption, accidental deletion, or catastrophic events affecting multiple drives simultaneously.

Whether you are a system administrator, a data recovery specialist, or an enthusiast managing your RAID array, the key to successful RAID management and recovery is understanding the underlying concepts, being prepared with thorough backups, and approaching both routine management and recovery tasks methodically and with patience.

By leveraging mdadm effectively and understanding the processes and limitations of RAID 5, you can ensure the integrity and reliability of your data, maximizing the benefits of this powerful storage technology while minimizing the risks associated with data loss.

Learn more on how to recover RAID 5 data!


  • How do I rebuild RAID 5 drive failure?

    Efficiently Restore Data from RAID 5 Following a Single Drive Failure

    Begin by accessing the RAID controller to identify the failed drive, documenting its details. Proceed to substitute the defective drive with a new or existing spare within the configuration. This action prompts the RAID controller to commence the reconstruction of the RAID array, utilizing data from the remaining drives. After the completion of the rebuild, your RAID 5 array will be fully functional once more.

  • How to recover a RAID in Linux?

    Restoring RAID in Linux Using Rescue Mode

    • Boot into "linux rescue" using a CD.
    • Utilize "mdadm" to reassemble the array.
    • Employ "mdadm" to mark one disk as failed and integrate a replacement disk.
    • Accelerate the RAID resynchronization operation. Reconfigure grub (the boot loader).
    • Transition an ext2 file system to ext3 (prompted by an inadvertent execution of "fsck" instead of "fsck.ext3").

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