The Microsoft Exchange Team has published some good articles about Exchange 2010 and high availability. The main subject is the database availability groups which are available in Exchange 2010.

In Exchange 2007 CCR and SCR where introduced. You needed a Windows Cluster first to create these high availability scenarios. This was especially difficult if you already had Exchange, but wanted to add high availability afterwards. Then you would need a migration scenario, which made things more complicated. CCR and SCR are gone in Exchange 2010 and replaced with the DAG (Database Availability Group).  With DAG you can have up to 16 Exchange Servers replicating databases across eachother, without the need to create a Windows Cluster first.

When the first server is added to a DAG, Windows will install the Windows Failover Clustering component if it’s not installed yet. In the background a cluster is created using the name of the DAG and a cluster network object (CNO) is created in the built-in Computers OU. An IP address is assigned to the DAG. This is done by using the DatabaseAvailablityGroupIpAddresses parameter of the Add-DatabaseAvailabilityGroupServer cmdlet, or by omitting this parameter and allowing the DAG to obtain an IP address by using a DHCP server on your network. A host record (A record) is created in DNS.

There are a few other things you need to know about Database Availability Groups:

  • You need a Windows Enterprise Server or Datacenter before you can add a server to a DAG. This is due to the Failover Clustering component requirement.
  • You need Exchange 2010 Enterprise edition
  • The server needs to have at least 2 physical NIC’s in order to be supported
  • DAG’s are for Mailbox databases, not for Public Folder databases
  • You can replicate 1 database to multiple Exchange Servers which are part of the DAG
  • All database names in your Exchange 2010 environment need to be unique
  • All copies of a database use the same path on each server containing a copy

For more information, you can watch the movies created by the MSExchangeTeam: movie1, movie2, movie3, movie4