AU Monolith Devices with Bad Pages

In the market for USB flash drives, many monolithic devices can be found. Often, these devices contain Alcor Micro (AU) controllers. While most of them function in a standard way, some exhibit unique characteristics. It is possible applied XOR, bit errors are removed, and proper block order—yet the file structure remains non-functional, and RAW files are corrupted.

Blocks are in the correct order, the bitmap is free of bit errors

The MBR is correctly positioned, but the file system is not working

Understanding the Issue

The root cause of this issue lies within the bitmap. Instead of using a logical image, it is necessary to use the Arranger element in VNR. By doing so, VNR exports full blocks in the correct order.

Arranger element in use

Within the Arranger element, finding high-entropy data such as images or videos can be helpful. In these cases, certain pages may repeat within blocks. If the repeated pages appear in the same positions across all blocks, this likely indicates the presence of bad pages.

Pages repeating in the same positions across all blocks

Resolving the Bad Pages Issue

To address bad pages, the block structure must be modified within the Arranger element:

Enable structure mode and navigate to Block structure.

Remove the existing Page structure in Block.

Add a Bad Page structure with the same size as a normal page.

Inside the block, add Page structures one by one. Where repeated pages occur, mark all but one as Bad Pages, keeping only the last repetition as the correct one.
Useful is set different colours for structures.

Once all pages are correctly marked in the block structure, use the Data Area element to extract the valid data while skipping the bad pages. After this operation, the full file structure should be recovered.

Final file structure after processing

Handling Multi-Plane XOR Variations

Some devices utilize different XOR keys for different planes, with each plane corresponding to a separate bank of blocks. To handle these cases:

Use the Plane Divider option to split the dump into individual planes.

Repeat the previous steps for each plane separately, as bad page positions may vary between planes.

Once the Data Area has been extracted from all planes, merge them using the Concatenate element.

Following these steps should ensure full file structure recovery.

Conclusion

Recovering data from AU monolithic devices with bad pages requires careful identification and handling of repeated pages. By leveraging VNR’s Arranger element and modifying the block structure, it is possible to isolate and bypass bad pages, allowing for a successful reconstruction of the file system. Additionally, when dealing with multi-plane devices, proper XOR key handling and structured processing per plane are essential for full data recovery. Implementing these techniques can significantly improve success rates in AU monolithic flash  data recovery.

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