During a department move, you migrate files from a file server to OneDrive for Business. Some files do not appear in the target OneDrive folder after the migration completes. This problem usually occurs because of file name or path length limits, hidden files, or permission restrictions that the migration tool does not report. This article explains the technical reasons behind missed files and provides specific steps to locate and recover them.
Key Takeaways: Recovering Missing Files After a OneDrive Migration
- Migration report log (CSV): Contains the exact reason each file failed — use it to filter for “Failed” or “Skipped” entries.
- Windows character restrictions: < > : ” / \ | ? Files with these characters in the name are blocked by OneDrive and must be renamed before upload.
- OneDrive path length limit of 400 characters: Files with a full path longer than 400 characters are silently skipped; shorten folder names or move files higher in the folder tree.
Why OneDrive Migration Misses Files During Department Moves
When you move files from a file server to OneDrive, the migration tool — typically the SharePoint Migration Tool or a third-party mover — attempts to copy each file. OneDrive enforces strict file name and path rules that the file server does not. If a file violates any of these rules, the tool logs the failure and moves on. The original file stays on the file server.
The most common causes for missed files are:
Invalid Characters in File or Folder Names
Windows file servers allow characters such as &, #, and % in file names. OneDrive blocks files containing any of these characters: < > : ” / \ | ? Files with leading or trailing spaces are also rejected.
Path Length Exceeds 400 Characters
OneDrive sync has a maximum path length of 400 characters. The path includes the drive letter, folder names, and the file name. Deeply nested folders on a file server often exceed this limit. The migration tool skips these files without deleting them.
Hidden or System Files
Files with the Hidden or System attribute set in Windows Explorer may not be scanned by some migration tools. Desktop.ini and Thumbs.db are common examples. These files are not copied unless the tool is configured to include them.
Permission Denials
The account running the migration must have Read access to every file and folder being moved. If a department move transfers ownership or if access control lists are changed mid-migration, the tool may fail to read certain files. The error is logged as “Access Denied.”
File Locked by Another Process
Files that are open in another program, such as a shared Excel workbook or a database file, cannot be read by the migration tool. The tool skips the file and logs a “File in Use” error.
Steps to Find and Recover Missed Files After Migration
- Open the migration report CSV
After the migration job finishes, download the report from the SharePoint Migration Tool or your third-party tool. The report is a CSV file named with the job ID and date. Open it in Excel. - Filter for failed and skipped files
In the report, apply a filter to the “Status” column. Select “Failed” and “Skipped” only. This shows every file that did not reach OneDrive. The “Error Message” column explains why each file failed. - Rename files with invalid characters
For each file listed with an invalid character error, open the source folder on the file server. Rename the file to remove the character. For example, change “Report:Q1.xlsx” to “Report-Q1.xlsx”. After renaming, re-run the migration job for the affected folder only. - Shorten paths that exceed 400 characters
Sort the report by “Full Path” and look for entries with a path length longer than 400 characters. Count the characters using the LEN function in Excel. Move the file to a higher-level folder on the file server, or rename deeply nested folders to shorter names. Re-run the migration. - Unhide hidden files before migration
On the file server, open the folder containing missed files. In Windows Explorer, go to View > Show > Hidden items. Select all hidden files, right-click, choose Properties, and uncheck Hidden. Then re-run the migration. - Grant full read permissions to the migration account
If the report shows “Access Denied” errors, have the file server administrator grant the migration account Full Control or at least Read & Execute permissions on the source folder and all subfolders. Retry the migration. - Close locked files
For “File in Use” errors, contact the user who has the file open. Ask them to close the file. If the file is a shared document, close it on all computers. Retry the migration for that folder.
If Files Are Still Missing After the Main Fix
Files appear in the OneDrive Recycle Bin
Occasionally, a file is uploaded but then immediately deleted by a sync conflict or a policy. Open the OneDrive Recycle Bin in a web browser at https://onedrive.live.com/recyclebin. If the file is there, select it and click Restore. The file returns to its original folder.
Duplicate files with same name were overwritten
If two files in different source folders have the same name, the second upload may overwrite the first. Check the migration report for “Overwrite” or “Keep Both” entries. If overwritten, retrieve the original file from the file server backup and upload it manually with a unique name.
Folder structure was flattened
Some migration tools flatten folder structures when the path is too long. Files may be moved to the root of the OneDrive folder instead of their intended subfolder. Scan the root of the OneDrive folder in a web browser for files that should be nested deeper. Move them to the correct folder manually.
File type was blocked by tenant policy
Your Microsoft 365 admin may have blocked certain file extensions, such as .exe, .bat, or .ps1. These files are rejected by OneDrive and will not appear. Check the migration report for “BlockedFileType” errors. To allow these files, the admin must go to the Microsoft 365 admin center > Settings > Org settings > OneDrive > Sync and remove the blocked extension from the list.
Migration Tool vs Manual Upload: Key Differences
| Item | SharePoint Migration Tool | Manual Upload via OneDrive Web |
|---|---|---|
| File name character check | Fails and logs invalid characters | Fails with a pop-up error message |
| Path length limit | 400 characters, silently skips | 400 characters, shows an error |
| Hidden files | Ignores by default | Uploads if selected |
| Permission check | Uses the migration account’s permissions | Uses the uploading user’s permissions |
| File in use handling | Skips and logs | Fails with a file-in-use error |
| Bulk rename feature | Not available | Not available |
| Report generation | CSV with detailed errors | No report |
The SharePoint Migration Tool is better for large department moves because it produces a detailed error report. Manual upload is suitable for small batches of files where you can fix errors immediately.
You can now locate every missed file using the migration report and correct the specific cause. After fixing the errors, re-run the migration job for the affected folders. To prevent future issues, run a pre-migration scan using the SharePoint Migration Assessment Tool. This tool checks file names, path lengths, and permissions before the actual move and generates a list of files that need attention.