If you’re not backing up any applications that use their own VSS provider, then consider selecting to use the System VSS Provider. I’m assuming the SQL Server databases files are not selected in this plan.

Thanks David. The same error did not occur on the following night's backup, so the backup completed successfully. I also changed the option to "use system VSS provider" as you suggested. However, I'm still interested to know if there is a "retry" option when such errors occur. Waiting 24 hours to retry the backup puts files not backed up at risk. At the same time, I don't want to retry the backup during the day when I see the email that the backup has failed.

The software actually uses automatic retry system as long as your system allows to perform such operations. I/O errors are tricky to avoid, since they happen outside of the software, so in some cases it's difficult to avoid situations like that.

Hi Matt,
From what I can see in the Windows Event Log, it looks like there may be a bug in Cloudberry Backup. I am submitting an issue report with the details. I'd appreciate your quick follow up and response there. I'd like to switch to Cloudberry, but this is a show stopper.
thanks,
Martin

I should add that the problem recurred last night, even though I switched to "use system VSS provider."

The backup has run successfully nightly for the past 4 nights... just an update.

Thanks for the update.I suggest to continue communication in the ticket if the issue persists and re-send us the logs.

If you are facing “File backup failure with "unable to flush I/O” issue then this error may be as a result of an issue with the VSS subsystem on the Agent machine or Hyper-V host caused by VSS not being able to quiesce data to the disk within the VSS timeout window. And the solution is to switch to “use system VSS provider.".