High availability of mailbox database

The Exchange mailbox database stores all the mail of the user and is a veritable mail repository. Therefore, ensuring the high availability of mailbox databases is the most important task for Exchange administrators. ExchangeServer2010 removes LCR, CCR, CSR and other functions from exchange server2007 and replaces them with "database availability group (Database Available Groups, referred to as DAG)". DAG provides fault tolerance at the mail database level. If two Exchange servers are configured and DAG is configured, the databases of the two Exchange servers will automatically keep data synchronized. The most important thing is that the realization of DAG function does not require expensive storage devices, and the DAG function can be realized between exchange servers in the same hardware configuration environment.