NAS QNAP HS-251 RAID Arrays: Mechanical and Logical Failures Recovery Guide

Contents

• Why Regular Data Recovery Tools Can’t Restore Files from RAID
• Key Information About the NAS QNAP HS-251
• How to Remove Hard Disks from Your NAS and Connect Them to a PC
  • Step-by-Step Data Recovery with Hetman RAID Recovery
  • How to Safely Recover Data from Disk Images
  • Where Are the User’s Files Actually Stored?
  • RAID Recovery Software: Detailed Comparison

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 QNAP 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.

How can the number of concurrent users or clients accessing a NAS QNAP HS-251 device affect data loss risks?

The number of concurrent users or clients accessing a NAS (Network Attached Storage) device like QNAP HS-251 can potentially affect data loss risks in the following ways:

1. Increased risk of accidental deletion: With more users accessing the NAS device simultaneously, the chances of accidental file deletion or modification may increase. A user might unintentionally delete or overwrite important data, leading to data loss.
2. Higher probability of file conflicts: When multiple users are simultaneously modifying the same file, conflicts can arise. If proper file versioning and conflict resolution mechanisms are not in place, it may result in data loss or corruption.
3. Performance impact: A large number of concurrent users accessing the NAS device can put a strain on its resources, such as CPU, memory, and network bandwidth. This increased load may lead to degraded performance, which can increase the likelihood of data loss due to timeouts, network errors, or system crashes.
4. Security vulnerabilities: More concurrent users mean a larger attack surface and increased potential for security breaches. If the NAS device is not properly secured or user access controls are not adequately implemented, unauthorized access or malicious activities by one user can compromise the data of other users, leading to data loss or theft.
5. Backup and recovery challenges: Managing backups and ensuring data recovery becomes more complex with an increased number of concurrent users. Coordinating and scheduling regular backups, verifying their integrity, and restoring data accurately can be more challenging when multiple users are actively using the NAS device.

To mitigate these risks, it is important to implement proper access controls, user permissions, and file versioning mechanisms. Regular backups should be performed and tested to ensure data can be restored in case of any data loss event. Additionally, educating users about best practices for data management and security can help minimize the risks associated with concurrent access.

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

Although the NAS HS-251 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.

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   How to Order Remote Data Recovery

Step-by-Step Data Recovery with Hetman RAID Recovery

This program restores data from damaged RAID arrays and is fully compatible with QNAP HS-251. 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.

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How to recover data from a QNAP

HS-251 has 2 HDD slots, and it supports the following array types:

• RAID 1;

NAS supports:

• ZFS;
• EXT4;
• EXT3;
• exFAT;
• FAT32 (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.

   

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.

   

Where Are the User’s Files Actually Stored?

The QNAP HS-251 network-attached storage keeps QTS (QuTS hero) 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