In the previous blog http://blogs.msdn.com/b/sqlserverstorageengine/archive/2011/12/22/AlwaysOn-setting-up-readable-seconary-replica.aspx I mentioned that there are two options to configure secondary replica for running read workload. The first option ‘Read-intent-only’ is used to provide a directive to AlwaysOn secondary replica to accept connections that have the property ApplicationIntent=ReadOnly set. The word ‘intent’ is important here as there is no application check made to guarantee that there are no DDL/DML operations in the application connecting with ‘ReadOnly’ but an assumption is made that customer will only connect read workloads. If you connect an R/W application using false claim ApplicationIntent=ReadOnly, the application will connect successfully but will fail on the first DML/DDL thereby leading to a surprise to the customer.
Specifically, the benefits of ‘Read_Intent Only’ are
Note, you can only specify option (i.e. ApplicationIntent=ReadOnly) with new clients shipped as part of SQL12. If you have an application that uses older client, then you will need to use ‘Yes’ option for the secondary replica to allow read workloads. With this setting, secondary replica will allow newer clients as well.