You can use the high-availability feature of Database Availability Group (DAG) backups
for enhanced data and service availability, and automatic recovery from failures. You can use
Exchange Server 2013 or later versions with DAG backups to improve Exchange Server data backups and
data recovery.
Beginning with Exchange 2013 SP1, you can also back up Exchange Server databases
in a Database Availability Group (DAG) environment without a Cluster Administrative Access Point
(CAAP).
A DAG environment includes the following functions:
A group of up to 16 mailbox servers that can host up to 100 mailbox databases
Up to 16 online copies of a database (1 active database and up to 15 passive databases)
Synchronous or lagged replication. With lagged replication, you can delay the replaying of logs
on target databases if, for example, there are time differences between source and target
databases.
Automatic migration and failover of active database copies
The following figure illustrates a DAG environment:Figure 1. Sample DAG environment
Database copies are mirrored on any node within the DAG. You can complete the following tasks:
Query DAG database copies, including status.
Manage full, copy, incremental, and differential backups of active and passive databases within
a DAG. You can create a backup from any active database copy, any passive synchronous copy, or any
lagged copy within the DAG. If you back up a lagged database copy, it might take more time to
restore the backup because the lagged copy can have more transaction logs to restore and replay. As
a best practice, create your backup from a passive synchronous copy and not a lagged copy.
Move an active database copy to other nodes.
Query all DAG database copy backups.
Restore all DAG database copy backups.
Restore data into an active database, from either active or passive database copy backups.
Restore data into a recovery or alternate database.
Process Individual Mailbox Restore (IMR) operations from a DAG database copy backup.
