Marcus opened Disk Management (diskmgmt.msc). He clicked Action > Attach VHD . The dialog hung for 45 seconds before spitting out: "Virtual Disk Manager: The virtual disk is corrupted or unreadable."
Next, he tried -> Edit Disk . The wizard froze at 12% while attempting to compact the drive. No dice.
He downloaded VHDTool (a small open-source CLI utility). Its job: analyze and fix the VHD footer/header alignment. repair corrupt vhd
He ran:
His hands went cold. That 4TB fixed-size VHD wasn't just any file. It was the last known good snapshot of a legacy SQL server for a municipal transit authority. The physical server had died three hours ago. The differential backups had been silently failing for six months. This VHD was the only lifeline. Marcus opened Disk Management (diskmgmt
The tool had detected that the dynamic VHD header had a checksum mismatch—likely from an unclean Hyper-V host shutdown. VHDTool recalculated the checksum and zeroed out the corrupted BAT entry that pointed to a non-existent sector.
Mount-VHD -Path E:\VHDs\prod_db_backup_2024.vhd -NoDriveLetter Get-Disk | Where-Object OperationalStatus -eq "OK" A new disk appeared: Disk 4 (Offline) . He brought it online, assigned a drive letter Z: , and held his breath. The wizard froze at 12% while attempting to
By 5:00 AM, the transit authority’s schedule database was back online. The city’s morning buses rolled out on time, never knowing that their entire route database had been hanging by a thread of manually repaired block tables.