A high-availability solution covers the impacts of a hardware or software failure and preserves application availability, reducing perceived downtime for customers.SQL Server high-availability solutions increase server or database availability.
RTO: Recovery Time Objective (RTO) is the amount of time it is intended for data or hardware to be restored following data corruption or hardware failure.
RPO: A Recovery Point Objective (RPO) is a point in time from which data can be restored. For example, if there is data corruption, loss, or unavailability, when can a valid copy of the data be recovered? RPO is typically measured in minutes, hours, days, weeks, and so on.
What high availability options are available in SQL Server?
At a high level, there are five key high-availability alternatives, including a new feature set that will be released with SQL Server 2012 and later:
• Log Shipping
• Mirroring
• Replication
• Clustering
• AlwaysON