FreeFileSync NAS Backup Failed: SMB and Windows Checks
Quick answer
For failed NAS jobs, check share availability, path, credentials, permissions and logs before changing synchronization rules or retrying Mirror.
Validate the exact SMB share
Open the UNC path from the same Windows account that runs the job; confirm you reached the expected folder.
Check access and stability
Test read and write access with disposable files, then review network disconnects, VPN and power-saving behavior.
Inspect the preview for dangerous changes
Unexpectedly empty destination folders or mass deletions are reasons to stop and investigate, not to proceed.
Finish with a restore test
Run a small confirmed copy, review the log and open the copied file directly from the NAS share.
Before you run the job
Use disposable test folders for the first pass. Keep an independent copy of important files, confirm drive identities, and run Compare before Synchronize. A preview is not a substitute for checking the actual destination afterwards.
Related FreeFileSync Windows guides
Source and review notes
This guide explains a focused Windows workflow. Consult the current FreeFileSync developer manual for precise behavior and edition-specific options. Review each planned file operation and test with non-critical files before relying on a procedure.