If you like to backup your Exchange server by using windows backup you need to make .reg changes on the DAG member host Active/passive database. Reg changes are very simple and does not need any reboot. Lets say you have 3 Exchange servers configured in DAG and all servers do have active/passive databases……….
Using Windows Server Backup on Database Availability Group MembersIf a server hosting the data being backed up is a member of a database availability group (DAG) and hosts both active and passive database copies, you must disable the Microsoft Exchange Replication service VSS writer. If the Microsoft Exchange Replication service VSS writer is enabled, the backup operation will fail.
Add a new DWORD value named EnableVSSWriter, and set its value to 0.Exit Registry Editor and then restart the Microsoft Exchange Replication service
See sky drive for creating backup……………