Case Study: Recovery from a Compaq ProLiant RAID 5 Array Following a Partial and Corrupt Rebuild of Virtualized Servers
Client Profile: Business using a Compaq ProLiant server with a 7-disk RAID 5 array, running Small Business Server with multiple virtual machines.
Presenting Issue: Following a single disk failure and subsequent replacement, the RAID controller reported a successful 100% rebuild. However, the server failed to boot. HP Business Support upgraded firmware and ran diagnostics but could not resolve the issue, which was later identified as a partial rebuild that only completed 42%.
The Fault Analysis
This scenario represents a catastrophic logical corruption within a complex storage hierarchy. The failure occurred at multiple levels:
Physical Media Failure: The original member disk suffered an electromechanical failure, likely a spindle motor seizure or bearing failure, causing the drive to drop from the array.
RAID Controller Logic Error: The core of the failure was a critical bug in the RAID controller’s firmware. The controller incorrectly reported a 100% successful rebuild when, in fact, the process halted at 42%. This created a false positive success state, masking the underlying corruption. The partial rebuild wrote inconsistent data across the new disk, creating a split-brained array where some stripes had updated parity and data, while others remained in the degraded state.
File System Corruption: The Windows Small Business Server, installed on a Virtual Hard Disk (VHD/VHDX) or similar virtual disk file, has a multi-layered structure. The partial rebuild corrupted the NTFS file system within the virtual disk, specifically damaging critical metadata like the Master File Table ($MFT) and the NTFS $LogFile.
Virtualization Layer Corruption: The virtual disk files themselves are complex containers. A partial rebuild can corrupt the virtual disk header, parent disk links (in differencing chains), or the block allocation table (BAT) within the VHDX file, rendering the entire virtual machine inaccessible.
The Professional Data Recovery Laboratory Process
Recovery required a multi-stage forensic approach to first stabilize the physical media, then manually reconstruct the RAID, and finally decode the virtualized layers.
Phase 1: Physical Drive Stabilization and Forensic Imaging
We received 8 disks: the 7 original array members and the 1 new disk used in the failed rebuild.
Individual Drive Diagnostics: All 8 drives were connected to our PC-3000 system and DeepSpar Disk Imager for individual sector-level diagnostics and health assessment.
Motor Transplant on Failed Drive: The original failed drive was confirmed to have a spindle motor failure. In our Class 100 ISO 5 cleanroom, we performed a platter transplant, moving the entire stack of platters and the head stack assembly into an identical donor drive with a functional motor and PCB. This is a critical step to ensure all original data is accessible for the reconstruction.
Sector-Level Imaging: A full, sector-by-sector clone of all 8 drives was created onto our secure storage array. The imaging process for all drives was configured with read retry algorithms to handle any marginally unstable sectors, ensuring the most complete dataset for the subsequent logical reconstruction.
Phase 2: RAID Parameter Analysis and Virtual Reconstruction
With 8 forensic images, the task was to determine the correct state of the array.
Empirical Parameter Calculation: The RAID metadata on the controller was unreliable. Our software performed a block analysis across all 7 original disk images to empirically determine the RAID 5 parameters: stripe size (e.g., 64KB, 128KB), disk order, parity rotation algorithm (left-symmetric, right-symmetric), and data start offset.
Identifying the Rebuild Corruption: We then introduced the image of the new disk used in the partial rebuild. By performing a binary comparative analysis at the stripe level, we identified the exact LBA range (0% to 42%) where the rebuild had written new data and parity. This 42% portion was now a dangerous mix of old and new data.
Building a Coherent Virtual Array: We created two virtual RAID assemblies in our software:
Pre-Failure Array: Using only the 7 original disk images (including the now-recovered original failed drive), we built a virtual RAID 5 representing the array in its last known consistent state, prior to the rebuild.
Post-Rebuild Array Analysis: We analysed the corrupted 42% rebuilt section to determine which stripes, if any, contained valid data that was more recent than the pre-failure state.
Phase 3: Virtual Machine Container Reconstruction and Data Extraction
This was the most complex phase, dealing with the layered data structures.
Virtual Disk File Carving: From the coherent virtual RAID image, we located the large virtual disk files (e.g.,
.vhd,.vhdx,.vmdk). These files were likely fragmented across the array.Virtual Disk Metadata Repair: Using specialized virtual disk parsing tools, we repaired the corrupted VHDX header and Block Allocation Table (BAT). The BAT, which maps sector offsets within the VHDX file to sectors on the host, was critically damaged by the partial rebuild. We manually rebuilt it by analysing the internal file system structures of the guest OS.
Guest File System Recovery: Once the virtual disk containers were logically repaired, we mounted them and processed the internal file systems (NTFS for Windows Server). We repaired the $MFT using its mirror (
$MFTMirr) and replayed the NTFS $LogFile to achieve a transactionally consistent state.Application-Level Consistency Check: For the recovered virtual servers, we verified the integrity of critical application data, such as the Active Directory database (NTDS.dit) and Exchange Server database (.edb), to ensure they were recoverable and consistent.
Conclusion
The client’s server failure was a multi-layered disaster: a physical drive failure was compounded by a critical RAID controller firmware bug that falsely reported a successful rebuild, which in turn corrupted both the physical RAID stripes and the logical virtual disk structures. A professional lab’s success in this scenario hinges on the ability to perform physical drive recovery, forensically reconstruct the RAID array by ignoring the controller’s faulty metadata, and then meticulously repair the complex, layered data structures of virtualized environments. This process effectively “de-virtualizes” the recovery to access the core file systems.
The recovery was a success. By using the original 7 drives to reconstruct the pre-failure array state, we achieved a 98% recovery rate for both virtual servers, including all critical business data, user accounts, and company emails.
Swansea Data Recovery – 25 Years of Technical Excellence
When your enterprise RAID system suffers a complex failure involving partial rebuilds and virtualized environments, trust the UK’s No.1 HDD and SSD recovery specialists. Our expertise extends from cleanroom physical repairs to the forensic reconstruction of complex storage virtualizations, ensuring business continuity after catastrophic data loss. Contact us for a free diagnostic.