In rare cases, SQL Backup Master may log the following error when attempting to perform a differential database backup:
Failed to create backup: Cannot perform a differential backup for database “XYZ”, because a current database backup does not exist.
This error occurs because the SQL Server backup chain for the specified database is being invalidated. Let’s review possible causes.
Possible Cause #1 – VSS (Volume Shadow Copy Service) Backups
Some third-party backup solutions will take a snapshot of your SQL Server database via the Windows Volume Shadow Copy Service. These snapshots will invalidate the current backup chain, thereby interfering with tools such as SQL Backup Master.
Important: SQL Backup Master 6 and later includes a Backup History report that can help identify when this problem occurs. Select the Reporting tab in the main product window and select the Backup History report. When viewing the report, look for entries that have the Is Snapshot field set to True. These backups are not being created by SQL Backup Master.
VSS creates database backups through a Windows system service called SQL Writer Service. When enabled, this service allows backup applications to copy SQL Server data files while SQL Server is running.
The solution in this case is simple – disable the SQL Writer Service, as follows:
- Press Windows + R keys to open the Run dialog, then type services.msc and press Enter.
- Find the SQL Server VSS Writer service and double-click on it.
- Click the Stop button to stop the service, when change the startup type to Manual.
- Click OK to finish.
When the service has been disabled, use SQL Backup Master to trigger a full database backup to re-establish the state of the backup chain.
Possible Cause #2 – Changing the Recovery Model
If the SQL Server database recovery model has recently changed, you should manually trigger a new full backup in order to reinstate the database backup chain. Once this is done, future differential backups should run successfully.
Possible Cause #3 – SQL Server 2005 Bug
Microsoft knowledge base article #921106 describes a bug in SQL Server 2005 that can cause this problem. The KB article also provides a hot fix.
Still Need Help?
If you’ve reviewed the above causes and solutions are still experiencing this problem, please feel free to contact our support team. We’re always happy to help.