FreeFileSync NAS Sync on Windows: Safe Setup Guide
Configure FreeFileSync with a NAS or SMB share on Windows and verify credentials, paths, permissions, and recovery.
Quick answer
A NAS can be temporarily unavailable, remounted under another identity, or slow to report directory contents. Treat a missing share as a failed backup, not as an empty destination to mirror.
What to check first
Test create, edit, rename, and delete permissions with the same account that will run the synchronization job.
Windows-specific factors
Choose Update, Mirror, or Two Way deliberately. Preview every deletion and conflict before the first production run.
Safer troubleshooting workflow
Plan for sleeping NAS devices, VPN drops, Wi-Fi interruptions, and unavailable shares. Logs should make these failures visible.
How to verify the result
Test recovery by opening files from the NAS and restoring samples to a separate folder.
Frequently asked questions
Should I change sync mode to fix this?
Not until the underlying cause is identified. First verify paths, permissions, comparison results, and logs.
Is a successful sync the same as a verified backup?
No. Important data should be checked at the destination and periodically restored to a separate location.
Related: all FreeFileSync Windows guides
NAS backup: test connectivity and identity
A NAS can be temporarily unavailable, remounted under another identity, or slow to report directory contents. Treat a missing share as a failed backup, not as an empty destination to mirror.
Create one small file on the source, perform a controlled comparison, synchronize and open the result directly from the NAS share. Review warnings and reconnect behavior.
- NAS share disconnects: Stop the job and restore the verified connection before rerunning.
- Permissions differ between desktop and scheduled task: Validate the scheduled account has read/write access to the exact share path.
- Unexpectedly many deletions appear: Confirm the correct NAS folder is mounted; cancel rather than accepting the preview.