This article addresses an issue that causes an SQL differential or transaction log backup to fail.
Full SQL backups run successfully but differential or transaction log SQL backups fail with an error similar to the following:
----- Error Messages -----
Unable to perform a Differential backup of database 'database', instance 'instance': It appears that the VSS SQL Server Agent was not used to perform associated backups for this database or the associated backup(s) for this database reside on a different DPU appliance. Please perform a Full on-demand backup of this database. Review the client log for additional information.
For more detailed information on backup failures and performance issues see Unitrends KB 5062 - Backup Failures and Performance Issues
Discontinue all backup routines within the SQL maintenance plans and/or other backup agents and then run a new SQL full database backup with the Unitrends SQL agent.
Alternatively, you may choose to run SQL full database backups only, which are not affected by other backup routines.
You should also determine why backups are being run outside of the Unitrends backup schedule and discontinue them.
SQL databases keep a chain of logs which track changes made to the SQL database since the time which the last SQL full database backup was run. If the log chain is broken, then subsequent differential and transaction logs backup cannot be complete due to missing data in the log chain.