RAID Controller Failure on NAS QNAP Turbo Station TS-421 / TS-421U: Recovery Strategies and Consequences

Contents

• Why Regular Data Recovery Tools Can’t Restore Files from RAID
• Key Information About the NAS QNAP Turbo Station TS-421 / TS-421U
• 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 a NAS QNAP Turbo Station TS-421 / TS-421U device's cache settings impact data loss risks?

The cache settings on a QNAP Turbo Station TS-421 / TS-421U device can impact data loss risks in the following ways:

1. Write Cache: The write cache is a temporary storage area where data is written before being permanently stored on the hard drives. Enabling write cache can improve write performance, but it also increases the risk of data loss in case of a power outage or system failure. If the cache hasn't been flushed to the hard drives, the data in the cache may be lost.
2. Read Cache: The read cache stores frequently accessed data, allowing for faster access times. However, if the read cache becomes corrupted or fails, it can result in data loss or data inconsistency.
3. RAID Rebuild: In case of a hard drive failure in a RAID configuration, the NAS device needs to rebuild the data from the remaining drives onto a replacement drive. During this process, the cache settings can impact the risk of data loss. If write cache is enabled, the rebuild process may be faster, but there is a higher risk of data loss if there is a power outage or system failure during the rebuild.

It is important to consider the potential risks and benefits of cache settings on a NAS device. If data integrity and safety are a priority, it may be advisable to disable write cache or use a UPS (Uninterruptible Power Supply) to protect against power outages. Regular backups are also crucial to mitigate the risk of data loss.

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

Although the NAS Turbo Station TS-421 / TS-421U 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 Turbo Station TS-421 / TS-421U. 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

Turbo Station TS-421 / TS-421U has 4 HDD slots, and it supports the following array types:

• RAID 5;
• RAID 6;
• RAID 10;
• RAID 0;
• RAID 1;
• JBOD;

NAS supports:

• ZFS;
• EXT4;
• EXT3;
• 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 Turbo Station TS-421 / TS-421U 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