Engineering teams migrating file servers to OneDrive for Business often discover that certain files are missing after the migration completes. This typically occurs because OneDrive blocks or skips files with unsupported characters, overly long paths, or specific file types that are common in engineering workflows. This article explains why engineering files get missed, provides a step-by-step process to identify and migrate those files, and covers related failure patterns such as broken shortcuts or file type restrictions.
Key Takeaways: How to Fix Missing Engineering Files in OneDrive Migration
- OneDrive sync app > Settings > Account > Choose folders: Use this to verify which folders synced and which are missing.
- Microsoft 365 admin center > SharePoint > Migration > Migration Manager: Central tool for bulk file server migrations with error reporting.
- OneDrive sync app > Pause syncing > Resume syncing: Simple restart that forces a full scan and can pick up missed files.
Why OneDrive for Business Misses Engineering Files During Migration
OneDrive for Business syncs files to SharePoint Online, which has strict naming and path length limits. Engineering environments often contain files that violate these limits, causing OneDrive to silently skip them. The most common root causes are file names with illegal characters like double quotes, colons, or pipes; file paths longer than 400 characters; and file types blocked by tenant policies such as .exe, .dll, or .pst.
Additionally, the OneDrive sync app does not support all file system features. Symbolic links, junction points, and files with alternate data streams are ignored. Engineering teams using CAD tools often have such structures in their project folders. When the migration tool or sync app encounters these, it logs an error but does not retry or alert the user.
Finally, Known Folder Move or automatic folder backup may exclude certain top-level folders if they are redirected by Group Policy. If the file server path is mapped to a drive letter that conflicts with OneDrive’s default sync locations, the migration can miss entire directory trees.
Illegal Characters in Engineering File Names
OneDrive and SharePoint Online reject file names that contain these characters: “, :, , <, >, ?, |, /, \, and the tilde ~ in certain contexts. Engineering files from software development, CAD, or simulation tools frequently use these characters in version identifiers or project codes. For example, a file named “Assembly_v2.1:final” contains a colon and will not sync.
Path Length Exceeded
The maximum path length for OneDrive sync is 400 characters. Engineering projects often have deep folder nesting such as Projects > ClientName > 2024 > Design > CAD > RevB > Subassembly > Parts. When a file name is added at the end, the total path can exceed 400 characters. OneDrive skips such files without warning the user.
Steps to Identify and Migrate Missing Engineering Files
- Run the OneDrive sync app diagnostic
Open OneDrive settings by right-clicking the cloud icon in the system tray. Go to Settings > Account > Choose folders. Compare the folder list against the original file server structure. Any folder that shows zero files or is missing entirely indicates a sync failure. - Check the sync error log
In OneDrive settings, go to Settings > Sync and backup > Advanced settings > View sync errors. This list shows each file that failed to sync along with the error code. Common error codes for engineering files are 0x8007007B for illegal characters and 0x8007007A for path length. - Use SharePoint Migration Manager for bulk reporting
Open the Microsoft 365 admin center. Go to SharePoint > Migration > Migration Manager. Create a new migration task for the affected file server share. After scanning, the task report lists every file that will be skipped with a reason. Export this report as a CSV file. - Rename or relocate problematic files on the source
Open the CSV report in Excel. Filter for files with illegal characters or path length errors. On the file server, rename those files to remove illegal characters. For path length errors, move files to a shallower folder structure. Repeat this until the report shows zero skipped files. - Re-run the migration or force a full resync
After fixing the files, restart the migration task in Migration Manager. If you are using the OneDrive sync app directly, pause syncing by right-clicking the OneDrive icon and selecting Pause syncing for 2 hours. Wait one minute, then click Resume syncing. This forces a full scan of all folders. - Verify file count and integrity
After the sync completes, compare the total file count in OneDrive online versus the original file server. Use a PowerShell script to count files in both locations. For engineering files, also spot-check a random sample of 50 files to confirm they open correctly in their native application.
If OneDrive Still Misses Files After the Main Fix
OneDrive Shows a Red X on Shared Engineering Files
A red X icon on a file in File Explorer means the file failed to sync. The cause is often a file lock held by an engineering application. CAD tools, for example, keep files open while the user is working. Close the application and wait 30 seconds. The red X should disappear. If it persists, right-click the file and select Free up space, then click Always keep on this device to force a fresh download.
Engineering Files with Symbolic Links or Junctions Are Missing
OneDrive does not follow symbolic links or junction points. If the original file server used these to point to files stored elsewhere, those files will not appear in OneDrive. Replace symbolic links with actual file copies before migration. Use the command robocopy source destination /e /copyall to copy the actual files to a flat folder structure.
File Type Blocked by Tenant Policy
Your organization may block certain file types at the tenant level. Engineering files like .dwg, .rvt, or .stp can be blocked if the admin added their extensions to the blocked list. Go to the Microsoft 365 admin center. Navigate to SharePoint > Policies > Access control > Block file types. Check the list and remove any engineering file extensions that should be allowed.
Files-On-Demand vs Always Keep on This Device: Key Differences for Engineering Files
| Item | Files On-Demand | Always Keep on This Device |
|---|---|---|
| Description | Files appear in File Explorer but download only when opened | Files are fully downloaded and stored locally at all times |
| Disk space usage | Minimal; only metadata and thumbnails occupy space | Full file size is consumed on the local drive |
| Engineering tool compatibility | Some CAD tools fail to open files that are not fully downloaded | Works reliably with all engineering applications |
| Offline access | Files must be downloaded manually before going offline | All files are available offline automatically |
| Sync behavior | Only files opened or marked as offline are synced | Every file is synced immediately after any change |
For engineering teams, Always Keep on This Device is the recommended setting to avoid missing file errors caused by delayed downloads. To enable it, right-click the root OneDrive folder in File Explorer, select Always keep on this device, and confirm the action.
You can now identify and migrate engineering files that OneDrive missed during a file server migration. Start by running the OneDrive sync diagnostic and checking the error log. Then use SharePoint Migration Manager to generate a full report of skipped files. Rename or relocate problematic files on the source before re-running the migration. For ongoing reliability, set engineering project folders to Always Keep on This Device to prevent sync delays from causing missing file errors.