RAID Controller Failure on NAS Synology RackStation RS4021xs+: Causes, Recovery Tips, and Data Recovery Solutions

Has your NAS Synology RackStation RS4021xs+ suddenly lost its network drive and you’re unsure what to do next? Did the RAID array collapse, making your files inaccessible? Is the device throwing errors during startup? Perhaps you accidentally rebuilt the RAID array or several hard drives failed at the same time?

RAID Controller Failure on NAS Synology RackStation RS4021xs+: Causes, Recovery Tips, and Data Recovery Solutions
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Synology RackStation RS4021xs+ NAS Data Recovery in 2025

In this step-by-step tutorial, we’ll show you how to rebuild your RAID and recover data from an RackStation RS4021xs+. We’ll walk through the most common causes of failure and demonstrate proven methods to restore files from a lost or degraded RAID array.

RAID Controller Failure on NAS Synology RackStation RS4021xs+: Causes, Recovery Tips, and Data Recovery Solutions

RAID Recovery™ 2.8
Recover data from damaged RAID arrays inaccessible from a computer.
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Why Regular Data Recovery Tools Can’t Restore Files from RAID

Conventional hard drives store user data by writing it sequentially across the disk surface, which means an entire file is typically located on a single drive. In contrast, when data is written to a RAID array, each file is split into multiple fragments. These fragments are then distributed and written in sequence across all the drives in the array. Depending on the configuration, fragment sizes can range from 2 KB to 2 MB, so every file is physically stored across several disks at once.

This approach significantly increases read and write performance — after all, writing two halves of a 1 GB file to two drives simultaneously is much faster than writing the full 1 GB to a single disk. However, this same mechanism makes file recovery far more complex.

Different RAID levels use different methods to distribute and protect data. On top of that, manufacturers like Synology often add their own proprietary structures and variations. As a result, data can be written to disks in many different formats, and each requires a specific approach during recovery.

Can the use of snapshot or versioning features on NAS Synology RackStation RS4021xs+ devices aid in data recovery after data loss?

Yes, the use of snapshot or versioning features on NAS Synology RackStation RS4021xs+ devices can aid in data recovery after data loss.

Snapshots are point-in-time copies of the data stored on the NAS device. They capture the state of the data at a specific moment, allowing you to restore files or folders to a previous version if they are accidentally deleted, modified, or corrupted. Snapshots provide a convenient way to recover data without relying on traditional backup and restore processes.

Versioning, on the other hand, keeps track of multiple versions of files, allowing you to roll back to a previous version if needed. This can be helpful if you need to recover a specific version of a file that was overwritten or modified incorrectly.

By utilizing these features, you can have an additional layer of protection against data loss and increase the chances of recovering your data in case of accidental deletion, ransomware attacks, or other data corruption incidents. It is important to regularly schedule snapshots and configure versioning settings to ensure that you have multiple restore points available.

How to Remove Hard Disks from Your NAS and Connect Them to a PC

Although the NAS RackStation RS4021xs+ can be accessed over the network, you still need to remove its hard disks and connect them directly to a Windows PC. Only then can the recovery software properly scan and analyze the drives. Follow these steps:

  1. Power off the NAS and disconnect it from the power source.

    WARNING! Before removing any drives, carefully read the device manual. Improper actions may damage both the NAS enclosure and the hard disks in the RAID array.

  2. Remove the hard disks one by one, gently sliding each drive out of its slot. Remember that hard disks are highly sensitive: any impact or drop can cause serious physical damage.

  3. Label each hard disk according to its position inside the NAS. The order of the drives is crucial for correct RAID reconstruction.

  4. Connect the drives to your computer. In this video, we explain which ports you can use to connect hard disks and what to do if your PC does not have enough free connectors.

    Go to view
    How to Order Remote Data Recovery

    How to Order Remote Data Recovery

Step-by-Step Data Recovery with Hetman RAID Recovery

Hetman Raid Recovery

This program restores data from damaged RAID arrays and is fully compatible with Synology RackStation RS4021xs+. Each hard disk in the array contains technical metadata describing how files were written. When launched, Hetman RAID Recovery analyzes this metadata, automatically reconstructs the damaged array, and provides access to its contents. After that, you can browse the recovered disk and save your files. The program can also restore files that were accidentally deleted from the network drive.

Go to view
How to recover data from a Synology

How to recover data from a Synology

RackStation RS4021xs+ has 16 HDD slots, and it supports the following array types:

  • Synology Hybrid RAID (SHR);
  • RAID 6;
  • RAID 5;
  • RAID 10;
  • RAID 1;
  • RAID 0;
  • Basic;
  • JBOD;

NAS supports:

  • Btrfs;
  • EXT4;
  • EXT3 (External Disk Only);
  • FAT32 (External Disk Only);
  • exFAT (External Disk Only);
  • NTFS (External Disk Only);
  • HFS+ (External Disk Read Only);

How to Safely Recover Data from Disk Images

This utility allows you to create a complete copy of a disk and work with the disk image instead of the physical drive. This approach helps protect your data from:

  • Overwriting during the recovery process;
  • Additional data loss caused by bad sectors;
  • User errors.

To create a disk image, follow these steps:

  1. Ensure you have enough free space to store the image. Its size will typically match the size of the original disk.

  2. In the main window, select the target disk and choose Tools - Save Disk. You can also select multiple disks if needed.

  3. When the Image Creation Wizard opens, select whether you want to save the entire disk or only a specific region. Adjust the settings and click Next.

    Hetman RAID Recovery: Image Creation Wizard

  4. Choose the directory where the image will be saved. You may select any available disk connected to your PC or upload the image via FTP.

    Hetman RAID Recovery: Choose a disk or save the image via FTP

Where Are the User’s Files Actually Stored?

The Synology RackStation RS4021xs+ network-attached storage keeps DSM (DiskStation Manager) operating system files on a separate RAID 1 (mirrored) array. Usually, all NAS systems create several volumes on every hard disk, and the first of them takes up to 2 Gb of space. This is where operating system files are stored. Other volumes are united into a RAID array where user’s data is written.

RAID Recovery Software: Detailed Comparison

Product Operating system RAID controller support Supported file systems Virtual RAID controller support Data recovery from damaged RAID File preview
Hetman RAID Recovery Windows, Linux, MacOS Yes, over 100 controllers FAT, exFAT, NTFS, ReFS, APFS, HFS+, Ext4, Ext3, Ext2, ReiserFS, Btrfs, VMFS, Hikvision, XFS, UFS, ZFS Yes Yes Yes
DiskInternals RAID Recovery Windows Yes, over 10 controllers FAT, NTFS, Ext2/3/4, HFS+ No Yes Yes
R-Studio Windows, Mac, Linux Yes, over 20 controllers FAT, NTFS, Ext2/3/4, HFS+ Yes Yes Yes
UFS Explorer RAID Recovery Windows, Mac, Linux Yes, over 100 controllers FAT, NTFS, Ext2/3/4, HFS+ Yes Yes Yes
EaseUS Data Recovery Windows Yes, over 20 controllers FAT, NTFS, Ext2/3/4, HFS+ No Yes Yes
ReclaiMe Free RAID Recovery Windows Yes, over 100 controllers FAT, NTFS, Ext2/3/4, HFS+ Yes Yes Yes

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  • Hetman Software: Data Recovery
    Hetman Software: Data Recovery 9.08.2022 12:31 #
    If you want to ask a question about data recovery, from NAS RackStation RS4021xs+, feel free to leave a comment!
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Vladimir Artiukh

Author: Vladimir Artiukh, Technical Writer

Vladimir Artiukh is a technical writer for Hetman Software, as well as the voice and face of their English-speaking YouTube channel, Hetman Software: Data Recovery for Windows. He handles tutorials, how-tos, and detailed reviews on how the company’s tools work with all kinds of data storage devices.

Oleg Afonin

Editor: Oleg Afonin, Technical Writer

Oleg Afonin is an expert in mobile forensics, data recovery and computer systems. He often attends large data security conferences, and writes several blogs for such resources as xaker.ru, Elcomsoft and Habr. In addition to his online activities, Oleg’s articles are also published in professional magazines. Also, Oleg Afonin is the co-author of a well-known book, Mobile Forensics - Advanced Investigative Strategies.

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Questions and answers

  • How does the Synology RackStation RS4021xs+ function as a VPN server, and what are its key features in this regard?

    The Synology RackStation RS4021xs+ is a high-performance network-attached storage (NAS) device that can function as a VPN server. Here are its key features in this regard:

    1. VPN Protocols: The RS4021xs+ supports various VPN protocols, including OpenVPN, L2TP/IPSec, and PPTP. These protocols ensure secure and encrypted connections between remote devices and the NAS.
    2. Remote Access: With the RS4021xs+ acting as a VPN server, users can securely access their files and services on the NAS from anywhere in the world. This enables remote working capabilities and enhances productivity.
    3. Site-to-Site VPN: The NAS can establish secure connections between multiple offices or branches using site-to-site VPN. This allows seamless file sharing and collaboration across different locations.
    4. VPN Plus Server Package: Synology offers the VPN Plus Server package, which provides additional features and capabilities for the RS4021xs+. It includes features like point-to-site VPN, client VPN profile management, and a web portal for easy access.
    5. High Performance: The RS4021xs+ is equipped with a powerful Intel Xeon processor and ample RAM, ensuring high-speed VPN connections and efficient data transfer.
    6. Security and Encryption: The NAS supports strong encryption algorithms, such as AES-256, to ensure data privacy and protection during VPN connections. It also offers firewall and IP blocking features to enhance security.
    7. User Management: The RS4021xs+ allows administrators to create and manage user accounts with different access privileges. This enables granular control over VPN access and enhances security.
    8. Intuitive User Interface: Synology's DiskStation Manager (DSM) operating system provides a user-friendly interface for managing the VPN server settings. It offers easy setup, configuration, and monitoring of VPN connections.

    Overall, the Synology RackStation RS4021xs+ offers robust VPN server capabilities with its extensive features, high performance, and secure connections. It is suitable for businesses and individuals looking for a reliable and secure VPN solution integrated with their NAS.

  • What are the advantages and benefits of using the Synology RackStation RS4021xs+ as a VPN server compared to other solutions available in the market?

    The Synology RackStation RS4021xs+ offers several advantages and benefits as a VPN server compared to other solutions available in the market:

    1. High-performance hardware: The RS4021xs+ is equipped with a powerful Intel Xeon processor and up to 64GB of RAM, ensuring smooth and efficient VPN performance even with heavy workloads or multiple concurrent connections.
    2. Scalability: The RackStation RS4021xs+ supports up to 40 drive bays, allowing for massive storage capacity and the ability to handle large amounts of data. This makes it suitable for businesses with growing VPN demands or those requiring extensive storage for VPN logs or backups.
    3. Flexible VPN protocols: The RS4021xs+ supports various VPN protocols, including OpenVPN, L2TP/IPSec, and PPTP, giving users the flexibility to choose the most suitable protocol for their specific needs and compatibility requirements.
    4. High-security features: Synology provides comprehensive security features for the RS4021xs+, including firewall, intrusion prevention, and advanced encryption algorithms. This ensures that data transmitted through the VPN server remains secure and protected from unauthorized access.
    5. User-friendly management interface: Synology's DiskStation Manager (DSM) operating system provides a user-friendly web-based interface for managing the RS4021xs+. It offers intuitive setup wizards, monitoring tools, and VPN server configurations, making it easy for both IT professionals and non-technical users to set up and manage VPN connections.
    6. Integration with other Synology services: The RS4021xs+ seamlessly integrates with other Synology services and applications, such as Synology Drive, Active Directory Server, and Synology Office, allowing for centralized user management, file sharing, and collaboration within the VPN environment.
    7. Extensive third-party app support: Synology's DSM supports a wide range of third-party applications through its Package Center. This enables users to extend the functionality of the RS4021xs+ VPN server by installing additional apps, such as VPN clients, monitoring tools, or security add-ons.
    8. Reliability and redundancy: The RS4021xs+ supports various RAID configurations, including Synology Hybrid RAID (SHR), which provides data redundancy and protection against drive failures. Additionally, it supports Synology High Availability (SHA) for seamless failover and continuous VPN service availability in case of hardware or network failures.

    Overall, the Synology RackStation RS4021xs+ offers a powerful, scalable, and secure VPN server solution with a user-friendly interface and extensive integration options, making it a highly advantageous choice for businesses requiring advanced VPN capabilities.

  • Can the Synology RackStation RS4021xs+ support multiple VPN protocols, and how does it ensure secure and reliable remote access to networks for businesses?

    Yes, the Synology RackStation RS4021xs+ can support multiple VPN protocols, including OpenVPN, L2TP/IPSec, and PPTP. These protocols provide flexibility and compatibility with various client devices and operating systems.

    To ensure secure and reliable remote access to networks for businesses, the RS4021xs+ incorporates several features:

    1. Secure VPN Connections: The RS4021xs+ uses industry-standard encryption algorithms and protocols to secure VPN connections. It supports up to 256-bit AES encryption, ensuring data confidentiality and integrity during transmission.
    2. Two-Factor Authentication (2FA): Synology's DSM operating system, which runs on the RS4021xs+, supports 2FA. This adds an extra layer of security by requiring users to provide a second form of authentication, such as a one-time password or fingerprint, in addition to their credentials.
    3. Firewall and Intrusion Prevention System (IPS): The RS4021xs+ includes a built-in firewall and IPS to protect against unauthorized access and network attacks. These features help detect and block suspicious activities, ensuring only legitimate VPN connections are allowed.
    4. VPN Server Management: Synology's DSM provides a user-friendly interface for managing VPN server settings, including user access control, connection logs, and traffic monitoring. This simplifies the setup and management of VPN connections, making it easier for businesses to maintain a secure and reliable remote access infrastructure.

    Overall, the RS4021xs+ offers robust security features and support for multiple VPN protocols, enabling businesses to establish secure and reliable remote access to their networks.
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