You are encountering failures with Exchange Full/Differential/Incremental backups.
The Full, might be successful, but the Incremental fail.
If you search the Status Logs of the backup, you find the following error:
----- Summary Messages -----
Exchange backup failed because circular logging is enabled
----- End Summary Messages -----
Unitrends follows Microsoft best practices and leverages VSS backup infrastructure for requesting, receiving, and restoring backup data. This requires that transaction logs are being used and can be referenced. Circular Logging does not leave a Transaction log to reference, thus the backup failure.
Circular logging creates the following restrictions:
If enabled during the backup operation or the recovery operation, you cannot restore individual databases.
Only point-in-time recovery operations are possible. When circular logging is enabled, you can delete transaction logs in the same directory when a database is restored, although those logs might be part of a different Exchange 2013 database.
You cannot perform incremental or differential backup operations. For more information about these types of backups, see Types of backup operations for Exchange 2013.
If circular logging is enables, your administrator should disable it as soon as possible to ensure that your VSS backups don’t fail. For more information, check out the blog post Exchange Circular Logging and VSS Backups.
The following below is based on Microsoft TechNet Document Exchange Circular Logging and VSS Backups...
When you configure an Exchange database with circular logging turned on, Exchange doesn’t wait until a backup occurs to truncate transaction log files. Rather, as soon as the log files have been played forward into the database, Exchange is free to delete those transaction logs...If you have circular logging turned on, when the incremental backup is performed, the log files that are expected to be there since the previous backup are not there – they have been truncated – causing the backup to fail.
Circular Logging is useful in a few scenarios:
- Customers leverage circular logging on mailbox databases that do not contain any user data.
- Customers leverage circular logging on mailbox databases within lab environments.
- Customers leverage circular logging on mailbox databases in Exchange 2010 when they utilize the Exchange Native Data Protection built into the product because there is no traditional VSS backup solution used to manage the log file truncations.