How Does Folder Sync Work on Windows?
Folder sync on Windows keeps two folders identical, either through the cloud or between drives. Use OneDrive to sync folders across computers, a free app like FreeFileSync to match folders on two drives, or the built-in Robocopy command for scheduled mirrors. Pick based on where the second copy should live.
| Method | Syncs between | Two-way? | Cost | Best for |
|---|---|---|---|---|
| OneDrive (built in) | PC and the cloud, then other devices | Yes | 5 GB free, paid plans for more | Access from any device |
| Google Drive for desktop | PC and Google Drive | Yes | 15 GB free, shared | Gmail and Android users |
| FreeFileSync | Any two folders, drives or network shares | Yes, or one-way mirror | Free | External drives and NAS |
| Robocopy (built in) | Any two folders | One-way mirror | Free | Scheduled, scripted copies |
| Syncthing | Two or more PCs directly | Yes | Free | Private PC-to-PC sync |
What You Need Before You Start
- Windows 10 or Windows 11 with the latest updates.
- An administrator account if you plan to schedule tasks.
- Enough free space on the target drive or cloud plan.
- A backup of the folder. Mirror tools can delete files on the target, so test with copies first.
Method 1: Sync Folders With OneDrive
OneDrive is the simplest folder sync on Windows because it is already installed. It syncs its own folder and can back up Desktop, Documents and Pictures.
- Open OneDrive from the Start menu and sign in with your Microsoft account.
- Click the OneDrive cloud icon in the taskbar, then Settings (gear icon).
- Open Sync and back up, then Manage back up.
- Turn on the folders you want: Desktop, Documents, Pictures, Music or Videos.
- For any other folder, move it inside your OneDrive folder.
For a full walkthrough with screenshots, see our guide on how to sync folders and files with OneDrive on Windows.
Method 2: Match Two Folders With FreeFileSync
FreeFileSync is a free, open-source app for Windows, Mac and Linux. It compares two folders and copies the differences. It works well for an external drive or a NAS share.
- Download FreeFileSync from its official site and install it.
- Choose the left folder (source) and the right folder (target).
- Click Compare to see which files differ.
- Choose a sync variant: Two way keeps both sides matched, Mirror makes the target an exact copy, and Update copies new files only.
- Click Synchronize. Save the job as a batch file to reuse it.
- To sync automatically, use the bundled RealTimeSync tool or schedule the batch file.
I prefer Update or Two way for most home users. Mirror is powerful but deletes target files that are missing from the source.
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Method 3: Schedule a Robocopy Mirror
Robocopy is a command-line copy tool built into Windows. It is fast, reliable and handles retries. It only works one way.
-
Open Notepad and paste this line, changing the paths to yours:
robocopy "C:Work" "D:WorkMirror" /MIR /R:2 /W:5 /LOG:"C:Logswork-sync.log" -
Save the file as
work-sync.bat. - Open Task Scheduler, choose Create Basic Task, and set a daily or hourly trigger.
- For the action, choose Start a program and select
work-sync.bat.
The /MIR switch mirrors the folder, including deletions. Run it once by hand and read the log before you schedule it. Microsoft documents every switch in its Robocopy reference.
Common Errors and Fixes
| Problem | Cause | Fix |
|---|---|---|
| OneDrive shows “can’t sync this file” | Blocked character, path over 400 characters, or file over 250 GB | Rename or shorten the path |
| FreeFileSync reports access denied | File open in another app or no permission | Close the app, or run the job as administrator |
| Robocopy deleted files on the target | /MIR mirrors deletions |
Use /E instead to copy without deleting |
| Folders sync but phone shows old files | Phone app has not refreshed | Open the app on Wi-Fi and pull to refresh |
| Two sync apps fight over one folder | Both watch the same files | Give each app its own folder |
If OneDrive itself stops syncing, our OneDrive not syncing guide has the full fix order. For any other app, start with sync issues.
How to Verify the Sync Worked
- Create a test file in the source folder.
- Run or wait for the sync.
- Confirm the file appears in the target with the same size and date.
- For two-way sync, edit the file on the target side and confirm the change returns.
- For Robocopy, open the log and check that the summary shows zero failures.
Ready to go further? Our guide to sync to the cloud covers the settings to choose on day one, and file sync explains how sync differs from backup.
Frequently Asked Questions
Does Windows have built-in folder sync?
Yes, in two forms. OneDrive comes with Windows 10 and 11 and syncs folders with the cloud and your other devices. Robocopy, a command-line tool, mirrors folders between drives. Microsoft retired its older SyncToy utility, so for a graphical tool between local drives, most people use FreeFileSync.
How do I sync two folders on different drives automatically?
Use FreeFileSync with its RealTimeSync helper, which watches the source folder and runs your sync job when files change. Alternatively, write a Robocopy batch file and schedule it in Task Scheduler. Test either method with copies first, because mirror settings delete files on the target.
Can I sync a folder to a NAS on Windows?
Yes. Map the NAS share as a network drive, then point FreeFileSync or Robocopy at it as the target. Many NAS brands also offer their own Windows sync apps. Keep the NAS on a wired connection for the first large copy, and see our NAS sync guide for options.
What is the difference between mirror and two-way sync?
A mirror makes the target an exact copy of the source, so changes and deletions only flow one way. Two-way sync copies changes in both directions and keeps both folders matched. Use a mirror for a simple copy you never edit, and two-way sync when you work in both places.
Why does OneDrive only sync some of my folders?
OneDrive only syncs its own folder and any known folders you turn on, such as Desktop and Documents. Folders elsewhere on the drive are ignored. Move them inside the OneDrive folder, or check that the folder is not excluded under Choose folders in OneDrive settings.
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