Because I deal a lot with HA/site resilience in my job as a Technology Architect, one of my favorite features in Exchange 2010 is naturally the new Database Availability Group (DAG) HA/site resilience feature, which replaces CCR/SCR/LCR. Also note that SCC has been deprecated/cut with Exchange 2010.
DAG built on the functionality we know from CCR and SCR, that is it still uses asynchronous log shipping and replay etc.
An interesting thing about DAGs is that you’re no longer required to form a cluster before you install the MBX server role. The limited cluster features that are used by DAGs (primarily cluster heartbeat and quorum) are configured automatically when adding the first MBX server to the DAG and thereby more or less invisible to the administrator.
With DAG you can have up to 16 copies of a Mailbox database. In addition, you can also have other Exchange 2010 server roles such as HT and CAS installed on the MBX server which is member of a DAG. Also, you can have DAG members located on different subnets and in separate AD sites.
There’s a lot to say about DAG, but I’ll stop here and instead let you know I currently am writing a multi-part articles series on this very subject. Look forward to seeing it published here on MSExchange.org in a near future.
– Henrik Walther