SIRIS, ALTO, and NAS: Error: "Exception caught during backup run: File system not recognized for [GUID]"



When you try to start a backup for a system protected by the Datto Windows Agent, you receive the error message, "Critical error during data transfer." On investigation of the agent logs, you see the following error recorded: "Exception caught during backup run: File system not recognized for [GUID]."


  • Datto Windows Agent


One or more Resilient File System (ReFS) volumes on the protected system have unrecoverable filesystem issues present.

The Windows Event log may look something similar to the following:

  Log Name: System
Source: ReFS
Date: 4/18/2019 11:58:30 PM
Event ID: 133
Task Category: None
Level: Error
Computer: <Redacted>
Description: The file system detected a checksum error and was not able to correct it. The name of the file or folder is "<unable to determine file name>."


Identify The Issue

Identify the volume having the issue (use the GUID to determine what volume it is) and exclude that volume from backups to confirm.

  • To find an event, you can review the agent log by navigating to your Protect Page → Show Backup Logs → Show Agent Logs
  • You can review the system logs to find an event, such as the one listed above. Look for events that occurred around the same time as the failed backups.  

Resolve The Issue

To resolve the issue, you must wait for the Resilient File System (external link), to heal itself automatically. Eventually, the ReFS volume should resolve the file system issue by itself, and backups should complete again. 

  • Once the file system heals, you will need to re-include the excluded volumes before they begin backing up again; your Datto appliance will not automatically re-include them.
  • Verify you have resolved the issue by running a test backup on the volume.

Additional Resources

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