what is hadr
HADR  is a H igh-A vailability and D isaster R ecovery solution introduced in SQL Server 2011 Code Named Denali to maximize availability for one or more of your user databases.[ More Information ].HADR helps to maintain :lease check my previous post, STEP BY STEP guide to implement HADR in SQL Server 2011 / DENALI with Screenshots, for more details. Note: Denali CTP1 supports only a single, asynchronous secondary replica.