VHDX BAT recovery
Dynamic and differencing VHDX files use a block allocation table, or BAT, to describe which payload blocks exist and where they are stored. BAT damage may make a disk appear empty, corrupt, or inconsistent even when many payload blocks remain readable.
Understand the symptom
For each logical block, the BAT records state and a file offset. Differencing disks also track sector bitmaps so reads can fall through to the parent. Recovery must distinguish unallocated, zero, fully present, and partially present states, then correlate candidate offsets with checkpoint lineage and guest structures.
What you may see
Files or partitions show holes where BAT entries no longer map valid payload blocks.
Hyper-V cannot reconcile child allocation or sector-bitmap state with its parent.
A checker finds impossible states, overlapping offsets, or locations outside the file.
A converter may substitute zeros for blocks it cannot map.
Protect the source
Dynamic blocks are not guaranteed to appear in guest-address order.
A failed consolidation can contaminate the best remaining base state.
Partially present blocks require reads from both child and parent.
Do this now
Stop all writes, merges, backups, replication, and automatic recovery tasks.
Keep base and child disks, configuration, logs, exports, and file timestamps.
Use a method that retains full file content and does not normalize holes or truncate ranges.
Record checkpoint names, merge attempts, host version, storage incident, and priority guest data.
NEPFOSYS process
NEPFOSYS tests entry ranges, states, alignment, overlap, and sector-bitmap relationships.
Candidate blocks are matched against guest partitions, file systems, and parent-child chronology.
Priority files are recovered from a reconstructed virtual view rather than an edited production chain.
A clear next step
Start a case with the exact symptoms, incident timeline, prior attempts, encryption details, and the files that matter most. NEPFOSYS will route the case to the appropriate DFW intake or nationwide mail-in path.
Start with a case reviewQuestions, answered
It maps guest logical blocks to physical locations and states inside dynamic or differencing VHDX files.
Fixed disks have different allocation behavior; the exact format and disk type must be confirmed before diagnosis.
No. Preserve and map the full chain before any operation that writes into a parent disk.
DFW local · Nationwide mail-in