Data storage for Microsoft Exchange Server is the Microsoft Exchange Information Store service, which contains both mailbox store and public folder store data. The Microsoft Exchange Information Store service uses a database engine called Extensible Storage Engine (ESE), which is a transaction-based database technology.
For creation of new database in Exchange 2013 you need to restart “Information Store” service on your Exchange database server.
Failed to mount database “DB Name”. Error: An Active Manager operation failed. Error: Couldn’t find the specified mailbox database with GUID “Guid Id”. [Database: DatabaseName, Server: Server name]
Restart the Information Store Service after adding new database.
On the Start menu, click Run, type services.msc, and then click OK.
In the Results pane, find the Microsoft Exchange Information Store service.
Right-click the service, and then click Restart.
Now it is recommended step to balance the memory allocation. So it recommended to create in your planned time.
Earlier it used to be a warning and database used to mount without Information Store restart. It was a recommended step to balance the server memory allocation which is why we have always recommended to create in your planned time when you can move all the roles out of the server.