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Last year SQL Server 2012 launched with a new choice for high availability and disaster recovery (HADR) called AlwaysOn Availability Groups. The AlwaysOn Availability Groups feature is similar to Database Mirroring which will be removed from SQL Server in a future release, but there are quite a few differences. In both cases, a replica of the data is maintained on another server for HA or DR purposes. Transactions are automatically sent to and replayed on the replica, or secondary copy of the data.
Here is a summary of the differences between Database Mirroring and AlwaysOn Availability Groups:
AlwaysOn Availability Groups
Maximum number of secondary databases
Requires Windows Clustering
Yes, however the SQL Servers can be stand-alone
Yes, requires witness server and high-safety mode
HA or DR
Each secondary independently configurable
Groups of databases
No, each database is configured separately
Multiple databases can be grouped to failover together
Can be used for reporting
Only against a database snapshot of the mirror
Active database is called
Connection to active database
Requires special connection string for failover
Redirection handled by Windows Clustering with a virtual name. Special connection string not required
Connection string to mirror or secondary database
Can be configured with an ApplicationIntent connection string to automatically redirect or can use traditional connection string with server name.