Issue

One of our customers has an availability group server with two nodes and four databases. He received a warning stating that the log file for one of the larger databases was full.

Customer failed to check AG sync status and removed the database from AG, assuming that this would fix the problem and allow the log file to be truncated. The log file was not truncating even after the database was removed from AG. He contacted our DBA team, requesting assistance because the system was in production and the log file drive was rapidly filling up.

When you’re a DBA, a problem that appears to be insignificant based on the error description may not be so when you probe further.
Our monitoring system just warned us that the ‘XYZ’ database was missing a differential backup, with an error message as follows:

“Cannot perform a differential backup for database “XYZ”, because a current database backup does not exist. Perform a full database backup by reissuing BACKUP DATABASE, omitting the WITH DIFFERENTIAL option. [SQLSTATE 42000]”

If you, like me, get this problem when trying to backup a SQL Server 2017 database on Azure, there are two likely causes.