SIRIS, ALTO, and NAS: Error: VSS Export error occurred mid-transfer on previous attempt; falling back to DBD



When you try to start a backup for a machine protected by the Datto Windows Agent, you receive the error message, "VSS Export error occurred mid-transfer on previous attempt; falling back to DBD."


  • Datto Windows Agent


  • Antivirus or firewall software is filtering port 3260 or port 3262 on the protected machine.
  • One or more VSS writers on the production machine are in an unstable state.
  • The "DattoProvider" service is not installed or is corrupt.
  • The "Datto VSS Provider" is not installed or is corrupt.


In the context of this error, "DBD" represents the use of the Datto Block Driver without VSS application awareness. This is a fallback mechanism that the Datto Windows Agent can use to capture a crash-consistent backup of a host in the event that a VSS backup is not possible. crash-consistent backup produces a snapshot similar to the state your protected system would be in following a hard reboot. Data in processing may not be saved properly.

1. Verify that the configuration of the protected machine meets the antivirus and networking requirements described in Getting Started with the Datto Windows Agent.

2. Evaluate the health of the VSS writers on the protected machine. Resolve any issues that you find.

3. Attempt another backup.

4. If the error still occurs, verify that the Datto VSS Provider is installed by typing vssadmin list providers at an elevated command prompt in Windows. If it is not listed, check under Services to verify that "Volume Shadow Copy Provider" is enabled, and then uninstall and re-install the Datto Windows Agent.

5. If you continue to encounter this error message, contact Datto Technical Support for further assistance.

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