When you create or modify your SQL Server database instance to run using Multi-AZ, Amazon RDS will automatically provision a primary database in one Availability Zone and maintain a synchronous "standby" replica in a different Availability Zone. In the event of planned database maintenance or unplanned service disruption, Amazon RDS will automatically fail over the SQL Server database to the up-to-date standby so that database operations can resume quickly without any manual intervention.

Multi-AZ is available with Microsoft SQL Server 2008 R2 and 2012 Standard and Enterprise Editions. The increased availability and fault tolerance offered by Amazon RDS for SQL Server Multi-AZ are well suited for critical production environments using SQL Server.