This case study documents the recovery of a 25 GB MongoDB 4.x database that suffered catastrophic metadata loss following a disk-related corruption event. By utilizing low-level collection carving, the AS Data Recovery team bypassed a factory-reset metadata state to achieve a near 100% restoration.

Client & Data Information

• Client Name: Confidential
• Data Type: MongoDB 4.x (WiredTiger Engine)
• Data Capacity: 25 GB
• Primary Issue: Disk-Level Corruption / Failed Self-Repair / Initialized Metadata

Incident Summary

Following a hardware-level disk failure, the client’s MongoDB database files became corrupted. In an attempt to restore service, the client executed a repair command. Unfortunately, because the underlying metadata was severely damaged, the repair process re-initialized the metadata files (WiredTiger.wt).

This resulted in a “factory reset” state: while the service could now technically start, it was completely empty. The links between the database names and the physical collection files were severed, making it appear as though all tables had been deleted.

Technical Analysis

Upon forensic analysis of the 25 GB data directory, AS Data Recovery engineers identified:

• Metadata Wipe: The WiredTiger.wt file was fresh and contained no pointers to the original data.
• Orphaned Collections: The physical .wt files (e.g., collection-7–829348.wt) remained on the disk but were “invisible” to the MongoDB engine.
• BSON Persistence: A hex-level scan of the orphaned files confirmed that the Binary JSON (BSON) data packets were intact, despite the loss of the logical file-system map.

Recovery Solution

The recovery strategy utilized Physical BSON Signature Carving. Since the MongoDB engine could no longer recognize the original collections, our engineers bypassed the logical layer. Using proprietary AS Data Recovery tools, we interacted directly with the raw .wt files. By identifying the unique headers and footers of BSON documents, we manually extracted the data and re-imported it into a fresh database environment.

Recovery Process

• Forensic Imaging: Created a bit-for-bit clone of the 25 GB directory to prevent any further data loss from the failing disk.
• Orphaned File Identification: Scanned the data directory to locate all physical collection files that were no longer indexed by the system.
• Document Extraction: Used specialized tools to parse the raw BSON streams from each .wt file, rebuilding the documents record by record.
• Schema Re-Mapping: Analyzed the extracted documents to identify their original collection origins and re-grouped the data.
• Data Verification: Migrated the records to a clean MongoDB instance, achieving a near 100% success rate within 2 hours.

Recovery Results

• Recovery Integrity: Near 100% (All critical collections restored)
• Recovered Volume: 25 GB
• System Status: Database fully operational on new hardware.
• Total Recovery Time: 2 Hours

Expert Reminder from AS Data Recovery: Running a repair on a corrupted MongoDB instance without a backup is extremely risky. If the metadata is damaged, the repair tool may initialize the database, wiping your table information. Contact AS Data Recovery professionals immediately if your database fails to start. We can extract data directly from physical files, even when metadata is lost.