Diff backup fails with error 3035 but log backup succeeds

Question

We have a SQL Server 2014 Enterprise where the DIFF backups fail.
This is the error message we get:

Msg 3035, Level 16, State 1, Server sqltest, Line 1
Cannot perform a differential backup for database 'database1', because a current database backup does not exsist. Perform a full database backup by reissuing BACKUP DATABASE, omitting the WITH DIFFERENTIAL option.

After analysing the output of the following query we noticed that a third party tool was taking snapshot backups.

    select top 20 bs.type,bs.database_backup_lsn,bs.checkpoint_lsn,bs.backup_start_date,bs.is_snapshot,
    bs.is_copy_only,bs.user_name
    from dbo.backupset bs
    where bs.database_name = 'database1'
    order by backup_start_date desc

According to Pinal Dave these tools use VSS to take a backup which is not a normal full backup.

What I don't understand is why LOG backups succeed? To my knowledge, they are also based on the last FULL backup.
Can somebody explain this difference to me?

Answer 1

A log backup is not based on the most recent full backup. It is based on the most recent log backup.

I.e., you can "skip" a full or differential backup when you restore log backups, as long as you have an unbroken chain of log backups.

As for your particular issue: Work with the backup software/vendor and see if you can make it perform the snapshot backups so they are seen as COPY_ONLY by SQL Server. Possibly a setting in your backup software.