OneDrive File Issues

Fix OneDrive Sync Delay When Uploading Large PST Files

Amos Gikunda Sep 30, 2026 869 views

Question details

The user needs to resolve a temporary sync delay error in OneDrive that occurs while trying to upload a massive 9 GB Outlook PST file.

How to Fix OneDrive Sync Delay When Uploading a Large PST File

Product: Microsoft OneDrive
Device & OS: Windows
Scenario: Uploading a large 9 GB Outlook data file (PST) to OneDrive for backup purposes.
Observed behavior: OneDrive displays an error message stating 'Sync Delay - You may be experiencing a temporary sync delay due to high service activity' and fails to complete the upload process.

Before you start

Ensure Outlook is completely closed before syncing, as active PST files cannot be properly uploaded. Verify that your OneDrive account has sufficient storage capacity to accommodate the 9 GB file and that you are connected to a stable, high-bandwidth network.

Solution 1Recommended

Reset OneDrive and Adjust File Sync Settings

Resetting the OneDrive application clears its cache and restores default sync behaviors, effectively bypassing temporary service activity delays.

Large files, especially 9 GB PST archives, can overwhelm the standard sync queue. Adjusting the on-demand settings and forcing a complete OneDrive reset clears background conflicts without deleting your files.

Disable Files On-Demand

Click the OneDrive cloud icon in your system tray, go to Settings, navigate to the Sync and backup tab (or Settings tab in older versions), and uncheck the 'Files On-Demand' feature to ensure files download and sync locally.

Pause and Resume Synchronization

Click the OneDrive taskbar icon, click the Help & Settings gear icon, and select 'Pause syncing' (choose 2 hours). Wait a few minutes, click the gear icon again, and select 'Resume syncing'.

Execute the Reset Command

Press the Windows Key + R on your keyboard to open the Run dialog. Copy and paste the command '%localappdata%\Microsoft\OneDrive\onedrive.exe /reset' and press Enter.

Update OneDrive Client

If the OneDrive icon does not reappear in the taskbar after a few minutes, open the Start menu and manually launch OneDrive. Ensure your client is updated to the latest version by downloading it from the official Microsoft release notes page.

Reset OneDrive and Adjust File Sync Settings

Do Not Sync Active PST Files: Never use OneDrive as an active location for Outlook PST files. Continuous read/write actions from Outlook will cause constant sync loops. Always keep the PST in a purely local folder while using Outlook, and only sync closed copies.

Solution 2

Verify Service Health and Contact IT Support

If multiple users in a corporate environment are experiencing this error, it indicates a Microsoft 365 backend issue rather than a local configuration problem.

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Frequently Asked Questions

Why does uploading a large PST file cause a temporary sync delay?

A 9 GB PST file requires significant bandwidth and continuous uploading. If Microsoft's servers are experiencing high traffic, or if the file is being touched by local background processes, OneDrive restricts the upload speed to prioritize server stability, resulting in a 'high service activity' delay.

Can I store my active Outlook PST file directly in OneDrive?

Microsoft strongly advises against storing an active PST file in OneDrive. When Outlook is open, it continuously reads and writes to the PST file, causing OneDrive to attempt infinite syncs. This frequently leads to sync delays, high CPU usage, and potential data corruption.

Will running the OneDrive reset command delete my local files?

No, running the '%localappdata%\Microsoft\OneDrive\onedrive.exe /reset' command will not delete any of your documents. It merely clears the local OneDrive cache and resets the synchronization connections, forcing the app to re-evaluate the sync queue.

How can I safely back up a massive PST file to the cloud?

To safely back up a large PST file, completely close Microsoft Outlook first. Copy the PST file from its original location and paste it into your OneDrive folder as a static backup. Ensure you have unmetered bandwidth before initiating the upload.

Document & File Issues