Prepare a Library Before Enabling Sync: Mistakes to Avoid

You want to use OneDrive sync with a SharePoint document library so your team can work on files offline. But if you enable sync without preparing the library first, you will see constant sync errors, missing files, and performance slowdowns. The root cause is that SharePoint libraries have structural limits and naming rules that the OneDrive sync engine cannot handle. This article explains the five most common mistakes people make before turning on sync and how to fix each one.

Why SharePoint Library Preparation Matters for Sync

OneDrive sync for SharePoint libraries uses the same sync engine that handles your personal OneDrive files. This engine expects a clean folder structure with short file names, no special characters, and a limited number of items. If your library contains deeply nested folders, files with names longer than 400 characters, or more than 300,000 items, the sync engine will stop working or produce errors.

SharePoint libraries themselves do not have the same strict limits. You can upload files with names up to 400 characters and create folders up to 14 levels deep. But the sync engine enforces tighter restrictions. When you enable sync on an unprepared library, users see error messages such as “We can’t sync this library because the file names are too long” or “Sync is paused due to too many items.”

The solution is to audit your library before turning on sync. Check item counts, file name lengths, folder depth, file types, and permission structure. Fixing these issues after sync is running is much harder because the sync engine will keep retrying failed items.

Mistakes to Avoid Before Enabling Sync

Each mistake below has a specific preparation step you must take before you ask users to click the Sync button.

Mistake 1: Ignoring the 300,000 Item Limit

1. Check the total item count in the library
   Go to the library settings page. Under Permissions and Management, click Storage Metrics. The page shows the total number of files and folders. If the count is above 300,000, sync will fail.
2. Reduce the item count below 300,000
   Move older files to a separate archive library. Use a retention policy to delete outdated drafts. If you must keep all files, split the content into multiple libraries and sync each one separately.
3. Set a view with a folder structure
   Even if the total library is under the limit, a flat view with more than 100,000 items will slow down sync. Use folders to group files so each folder contains fewer than 100,000 items.

Mistake 2: Using File Names Longer Than 128 Characters

1. Identify files with long names
   Use a SharePoint list view or a PowerShell script to find files where the name plus the folder path exceeds 400 characters. The sync engine cannot handle paths longer than 400 characters.
2. Shorten file names and folder names
   Rename files so each name is under 128 characters. Reduce folder depth to no more than 8 levels. A good target is a total path length under 260 characters.
3. Remove special characters from names
   The sync engine does not allow files with names containing the characters \ / : ? ” < > |. Rename any file that uses these characters.

Mistake 3: Including Unsupported File Types

1. Check the library for blocked file types
   OneDrive sync blocks file types that are executable or system files. Common blocked types include .exe, .msi, .bat, .cmd, .vbs, .ps1, .tmp, and .lnk. Go to SharePoint admin center > Policies > File types to see the full list.
2. Move or delete blocked files
   Remove these files from the library before enabling sync. If you need to distribute executable files, store them in a separate library that is not synced.
3. Add a warning note in the library description
   Tell users not to upload blocked file types. This prevents future sync errors.

Mistake 4: Enabling Sync on a Library with Broken Permissions

1. Review unique permissions on folders and files
   Open the library in SharePoint. For each folder or file, go to the ellipsis menu > Manage access. If you see “This item has unique permissions” instead of “Inherited from parent,” that item will cause sync problems.
2. Restore inheritance where possible
   Click Delete unique permissions on each item to return to inherited permissions. Only keep unique permissions on items that absolutely require them. Sync works best when all items inherit from the library.
3. Test sync with a small group first
   If you must keep unique permissions, enable sync for a test group of five users. Monitor for permission-related sync errors for one week before rolling out to everyone.

Mistake 5: Not Communicating the Sync Rollout Plan

1. Create a user guide for sync behavior
   Write a one-page document explaining that synced files are stored in the user’s OneDrive folder under the company name. Tell users not to move or delete the SharePoint folder in File Explorer.
2. Schedule a staged rollout
   Enable sync for one department at a time. Monitor the sync status in the OneDrive sync client for the first week. If errors appear, pause the rollout and fix the library.
3. Set a rollback plan
   If sync causes data loss or performance issues, you can stop sync for the library from SharePoint admin center. Users will keep a copy of the files in their local OneDrive folder, but changes will not sync back to SharePoint.

What Happens If You Skip Preparation

Sync Shows “We can’t sync this library”

This error appears when the library exceeds the 300,000 item limit or contains files with paths longer than 400 characters. Users cannot sync any files until you reduce the item count or shorten file names. The sync client will not give a detailed reason, so you must check the library manually.

Files Are Missing After Sync Completes

If a file name contains a blocked character such as a colon or an asterisk, the sync engine skips that file entirely. The file remains in SharePoint but does not appear in the user’s local folder. Users think the file was deleted. You must rename the file in SharePoint and then force a resync.

Sync Keeps Pausing and Restarting

This happens when multiple users sync the same library and one user has unique permissions on a subfolder. The sync engine retries the folder repeatedly, causing all users to see intermittent pauses. Remove the unique permission or move the folder to a separate library.

Prepared Library vs Unprepared Library: Sync Performance

Factor	Prepared Library	Unprepared Library
Item count	Under 300,000	Above 300,000
Max file name length	128 characters or fewer	Over 128 characters
Folder depth	8 levels or fewer	More than 8 levels
Blocked file types	None present	Contains .exe, .bat, .tmp
Permission inheritance	All items inherit from library	Multiple items have unique permissions
Sync error rate	Less than 1% of users	Over 20% of users

You can now prepare your SharePoint library for sync by checking item count, file names, file types, permissions, and user communication. Start with a single library that has fewer than 100,000 items and no unique permissions. Enable sync for a test group of five users and monitor the OneDrive sync client for errors for one week. Use the SharePoint admin center > Sync Reports to see which files failed to sync and fix them before expanding the rollout.