Assume that you use Availability Groups in Microsoft SQL Server. When you use a Volume Shadow Copy Services (VSS)-based application to back up an availability database, the backup operation may Freeze the system I/O indefinitely. This causes the rendering of any other successive operations to wait until VSS explicitly issues a Thaw. If you try to run a transaction log backup of the same database during this time, you may receive the following error message:
BACKUP failed to complete the command BACKUP LOG database_name. Check the backup application log for detailed messages.
Note Before you receive this error message, you may receive an error message that resembles the following:
I/O is frozen on database database_name. No user action is required. However, if I/O is not resumed promptly, you could cancel the backup.
This fix is included in the following cumulative updates for SQL Server:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.