What is the difference between a regular cluster (Failover Cluster) and AlwaysOn Availability Groups?

Failover Cluster and AlwaysOn Availability Groups are high availability technologies in SQL Server, but they differ in architecture and capabilities.

Failover Cluster:

• Based on shared storage accessible to all cluster nodes.
• In case of a node failure, automatic failover occurs to another node using the same storage.
• Provides high availability at the SQL Server instance level.
• Supports only one active node in the cluster (active-passive).

AlwaysOn Availability Groups:

• Do not require shared storage; data is replicated between nodes.
• Allow multiple database replicas, including multiple active readable secondaries.
• Provide high availability and scalability at the database level.
• Enable flexible replication and load distribution.

Thus, Failover Cluster provides server-level protection using shared storage, while AlwaysOn Availability Groups operate at the database level with replication and read scaling capabilities.