When to Give Up and Call a Professional

• Size: Is bigfile000 exactly 1,073,741,824 bytes (1GB) or 2,147,483,648 bytes (2GB)? If it's smaller, the file is truncated.
• Date Modified: Compare the timestamp with the update log (if available). A recent timestamp during a failed update suggests corruption.

1. Use HxD Hex Editor (free).
2. Open a known-good bigfile000 from a backup or another installation.
3. Compare the first 512 bytes (the header) with your corrupt file.
4. If the header is damaged, copy the header from the good file over the bad one (preserving the rest of the data).
5. Save and test.

He tried a force-mount, a desperate move that could wipe the data entirely. > ERR_ACCESS_DENIED_BY_FILE_OWNER