Exchange Transaction Logs do not get flushed after a full Backup of Exchange Information Store when used with Advanced Open File option.
However, if the Exchange databases are selected, the "Use Advanced Open File Option" setting has been checked, AND "Process Logical Volumes for backup one at a time" is selected Exchange database transaction logs may not be flushed. This happens if VSP is used as the provider for backup of the volume containing Transaction logs and VSS is used as provider for Exchange Information Store Backup. Job Log shows that Backup of Volume is done using VSP as the provider and Information Store uses VSS as the provider as shown below in an extract of the job log:
AOFO: Started for resource: "\\Exchange-TEST\Microsoft Information Store\test". Advanced Open File Option used: Microsoft Volume Shadow Copy Service (VSS).
Although, this issue does not occur if VSS is selected as the provider for backup of both Exchange database and the volume containing Transaction Logs.
This can be resolved by using any one of the following methods:
Creating a separate Backup Job for Backup of Information Store with or without Advanced Open File Option.
Using VSS as the provider for backup of the volume containing transaction logs as well as Information Store. If "Process Logical Volumes for backup one at a time" is selected as an option under Advanced Open file option. (Figure 1) VSP is used as a provider for Backup of Volumes. In order to make the provider as VSS, this option should not be selected. (Figure 2)
Once, the option is unchecked and a Snapshot Backup is performed, VSS would be used as a provider for backup of Volume containing Transaction logs and also for Backup of Exchange Database and Exchange Transaction Logs would be flushed after full Backup as expected. This can be confirmed from an extract of a job log of a job which flushes the transaction logs as expected: