The concept of Database Availability Group (DAG) was introduced in Exchange 2010, and it has gone through some key improvements in Exchange 2013 and some architectural changes in Exchange 2016. DAG provides the infrastructure to protect the content of your mailbox databases by making copies on other Mailbox servers in your organization, and hence, providing high availability and site resilience.
There is a difference between High Availability and Site Resilience, which is important to understand. We say a messaging system is highly available if all the components are working in a way that if one component fails, the service and the data fails over to one of the working servers automatically. Typically, high availability events are triggered by servers or components failing within a single datacenter. Whereas, in the case of Site Resilience, the service and data is restored with manual intervention from administrators.
In this chapter, you will learn about...