Recovery from a Failed Western Digital My Book

Case Study: Recovery from a Failed Western Digital My Book Thunderbolt Duo RAID 1 Array Following a Disrupted Rebuild Process

Client Profile: User of a WD My Book Thunderbolt Duo 4TB external RAID system.
Presenting Issue: A degraded RAID 1 (mirror) array entered a failed rebuild state, stalling at 7% over 24 hours. After a forced restart, the array became entirely inaccessible, with data unavailable on both physical drives.

The Fault Analysis

The client’s experience is a classic example of a cascading failure in a hardware-controlled RAID system. The initial failure of “Drive A” triggered a complex sequence of events that ultimately compromised the entire logical volume.

  1. Underlying Media Degradation on Drive A: The initial degradation of Drive A was likely caused by unstable sectors or a firmware issue that prevented the drive from responding within the RAID controller’s timeout threshold. This prompted the controller to mark the drive as failed and initiate a rebuild onto Drive B.

  2. Catastrophic Rebuild Failure: The rebuild process stalling at 7% is highly indicative of a critical issue with the source drive (the remaining “good” Drive B). The most probable cause is that Drive B contained marginal sectors or developing read instabilities. During the intense, sequential read stress of a rebuild, these weak areas failed, causing the process to hang. The 24-hour duration to reach 7% is itself a massive red flag, pointing to severe read retries and hardware ECC recovery attempts.

  3. Metadata Corruption: The client’s action of restarting the system during a hung rebuild was catastrophic. The RAID controller’s volatile memory, which was managing the partial rebuild, was cleared. Upon reboot, the controller re-analysed the drives and found an inconsistent state: Drive A was already marked as failed, and Drive B now had a partially written, non-synchronised copy of the data and corrupted RAID metadata. With a valid, synchronised mirror pair no longer present, the controller correctly reported the entire array as failed to prevent further data corruption.

The Professional Data Recovery Laboratory Process

Recovery in this scenario requires a forensic approach that completely bypasses the WD enclosure’s faulty RAID controller to manually reconstruct a coherent data set from the two physically compromised drives.

Phase 1: Physical Drive Stabilisation and Independent Forensic Imaging

  1. Drive Extraction & Isolation: Both hard drives are physically removed from the My Book Duo enclosure. This is critical to bypass the proprietary hardware RAID controller and any potential issues with the Thunderbolt bridge board.

  2. Individual Diagnostics: Each drive is connected to our PC-3000 system with a stable, lab-grade power supply. A full diagnostic is run to assess the physical health of each drive. We expect to find:

    • Drive A: A high count of reallocated sectors, pending sectors, and potentially uncorrectable errors.

    • Drive B: Evidence of read instability and marginal sectors that caused the rebuild to fail.

  3. Sector-Level Imaging: Using our DeepSpar Disk Imager, we create full, sector-by-sector clones of both drives. The imaging process for Drive B is configured with aggressive read retry algorithms and timeout extensions to gently negotiate the unstable sectors that caused the original failure. A bad sector map is generated for each drive, providing a blueprint of the damaged areas.

Phase 2: RAID 1 Mirror Analysis and Data Synchronisation

With two complete disk images, we manually reconstruct the mirror.

  1. Block-Level Comparative Analysis: Our specialised RAID recovery software performs a block-by-block comparison of the two drive images. The goal is to identify a “golden copy” of each logical block address (LBA).

  2. Building a Coherent Virtual Image: The software is instructed to create a single, optimal image by following a rule set. For each LBA:

    • If the data from both drives is identical and passes a checksum, it is used.

    • If one drive returns a read error (from the bad sector map) but the other provides good data, the good data is used.

    • If both drives return different data (indicating a point of de-synchronisation from the failed rebuild), we use heuristic analysis—such as checking for valid file system structures—to select the most likely correct version, typically from the drive that was not the source of the initial failure (Drive B, pre-rebuild).

  3. Handling Partial Rebuild Corruption: The 7% of the drive that was rewritten during the failed rebuild is identified and isolated. Data in this region from Drive B is considered highly suspect and is only used if Drive A’s corresponding sector is unreadable.

Phase 3: File System Reconstruction and Data Extraction

The final, synchronised virtual image is now processed for data extraction.

  • Partition Table and Volume Mounting: We parse the virtual image for a valid GUID Partition Table (GPT) and mount the primary data volume.

  • File System Integrity Check: The volume, likely formatted with NTFS or HFS+, is analysed for consistency. We specifically check the $MFT (Master File Table) for NTFS or the Catalog File for HFS+ for errors that may have occurred during the array failure.

  • Data Extraction and Verification: The client’s data is extracted based on the repaired file system metadata. We perform checksum verification on a sample of files to confirm the integrity of the recovery.

Conclusion

The client’s data loss was not due to two simultaneous drive failures, but to a cascading logical failure triggered by the RAID controller’s inability to handle a deteriorating drive (Drive B) during a rebuild operation. The professional lab’s success hinged on physically isolating the drives from the faulty RAID controller, forensically imaging them to handle their individual instabilities, and then using software to manually reconstruct a valid mirror by intelligently combining the best available data from both members, effectively undoing the damage caused by the aborted rebuild.

The recovery was successful. By using Drive A as the primary source and supplementing it with stable data from Drive B, we achieved a 99% data recovery rate, restoring the client’s complete file structure.

Bracknell Data Recovery – 25 Years of Technical Excellence
When your hardware RAID system fails during a critical process like a rebuild, trust the UK’s No.1 HDD and SSD recovery specialists. We possess the specialised hardware and software to deconstruct failed arrays and manually reassemble your data, resolving the complex logical corruptions that consumer-grade systems cannot. Contact us for a free diagnostic.