FreeFileSync USB Drive Disconnects During Sync
Recover safely when a USB hard drive or SSD disconnects during a FreeFileSync job.
Quick answer
Windows may assign a different drive letter or temporarily disconnect an external drive. Never launch an unattended synchronization against an unverified removable destination.
What to check first
Inspect cable seating, USB hubs, power delivery, enclosure temperature, and Windows event history if disconnects repeat.
Windows-specific factors
Run a fresh comparison instead of guessing where the interrupted operation stopped.
Safer troubleshooting workflow
Review logs and open destination files, especially large files that may have been active during the disconnect.
How to verify the result
Do not schedule unattended jobs until the same hardware path has completed repeated manual runs reliably.
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
Removable drive safety before a sync job
Windows may assign a different drive letter or temporarily disconnect an external drive. Never launch an unattended synchronization against an unverified removable destination.
Reconnect the drive, inspect its volume label and capacity, and compare one sample folder. Open a recently transferred file before considering the job complete.
- Drive letter changed: Update the stored path after confirming the volume identity.
- USB cable or power is intermittent: Stop and fix the hardware problem; a partial transfer is not a verified backup.
- Job unexpectedly shows an empty folder: Cancel and recheck the physical disk and exact target path.