The SQL Server AlwaysOn is a high availability and disaster recovery solution introduced by Microsoft in SQL Server 2012. It is a solution that provides comprehensive protection for your databases through a replication model that promotes continuous synchronization between primary and secondary servers.
AlwaysOn consists of two key parts: Availability Groups and Failover Clustering Instances (FCIs). Both are essential components in providing recovery in case of failures and maintaining business continuity.
Availability Groups, or AGs, are similar to database mirroring, where one or more databases are replicated across different servers. However, AGs are more robust as they allow for up to 8 replicas to be synchronized with the primary server. Additionally, AGs offer the possibility of reading on the secondary replicas, thereby boosting the performance of read operations.
Failover Clustering Instances, or FCI, is a SQL Server instance that resides on a Windows Server Failover Cluster (WSFC). FCIs ensure high availability at the instance level, dealing with recovery from hardware, operating system, or software level failures.
AlwaysOn is an effective disaster recovery solution that ensures business continuity, providing greater peace of mind in data management. With Availability Groups and Failover Clustering Instances, AlwaysOn allows SQL Server to serve more users and with better performance.