This case study documents the successful recovery of a Synology DS1821+ NAS running SHR-2 (Synology Hybrid RAID) after three simultaneous drive failures left the volume inaccessible. Through careful array reconstruction and Btrfs metadata repair, our team recovered the client’s complete business file archive with full data integrity.

Client & Data Information

• Client Name: Confidential
• Data Type: Synology DS1821+, SHR-2, Btrfs file system
• Data Capacity: 32 TB (8 x 4TB drives)
• Failure Type: Triple drive failure during automatic rebuild

Incident Summary

The client’s Synology DS1821+ NAS, configured with SHR-2 across eight 4TB drives, began reporting degraded status after one drive failed. During the automatic rebuild process, two additional drives dropped offline in quick succession, a common but often catastrophic scenario when aging drives are placed under the heavy read load of a rebuild. The volume became completely inaccessible, and DSM reported the storage pool as “crashed.”

Technical Analysis

Forensic analysis of the eight drives revealed:

• Rebuild Interruption: The rebuild process had only partially restored parity for the first failed drive before the second and third failures occurred, leaving the array in an inconsistent state.
• Btrfs Metadata Corruption: The abrupt interruption caused partial corruption to the Btrfs superblock and chunk tree metadata.
• Drive Viability: Of the three failed drives, two were mechanically sound and readable via imaging; the third exhibited early-stage head degradation requiring specialized imaging equipment.

Recovery Solution

Rather than attempting a live rebuild, which risked overwriting the remaining valid parity data, our engineers imaged all eight drives independently in a controlled environment. We then reconstructed the SHR-2 array parameters virtually, calculating the correct drive order and parity distribution before rebuilding the Btrfs volume in a sandboxed environment isolated from the original hardware.

Recovery Process

• Full Drive Imaging: Sector-by-sector images of all eight drives, including the two mechanically failed units.
• Array Parameter Reconstruction: Manual analysis to determine the original SHR-2 stripe configuration and drive order.
• Btrfs Superblock Repair: Reconstruction of the damaged superblock and chunk tree using backup metadata copies preserved elsewhere on the volume.
• Virtual Volume Mount: Mounting the reconstructed array as a read-only virtual volume to verify file system consistency.
• Full File Extraction: Copying the complete directory structure and file set to new, healthy storage.

Recovery Results

• Recovery Integrity: 99.8%
• Files Recovered: Complete business archive, including shared folders and Synology Active Backup data
• Downtime: Client resumed normal operations within 4 business days