What is an always on SQL Server availability group?
An Always On SQL Server Availability Group is a feature of SQL Server that allows you to create a highly available and resilient environment for your databases. It does this by creating one or more copies (replicas) of your databases on different servers and automatically failing over to a replica if the primary database becomes unavailable.
Availability databases are the databases that are included in an availability group. An availability group can contain one or more availability databases.
Availability replicas are copies of the availability databases hosted on different servers. There are two types of availability replicas: Primary replicas and secondary replicas. The primary replica is the main copy of the database and handles all read-write workloads. The secondary replicas are copies of the primary replica and are used for failover and offloading read-only workloads.
Availability modes refer to the level of availability of the availability replicas. There are two availability modes: asynchronous-commit mode and synchronous-commit mode.
In asynchronous-commit mode, the secondary replicas do not need to be synchronized with the primary replica in real-time. This means that the primary replica can commit transactions to the database even if one or more secondary replicas are unavailable. This mode provides lower levels of data protection but higher levels of performance.
In asynchronous-commit mode, the secondary replicas do not need to be synchronized with the primary replica in real-time. This means that the primary replica can commit transactions to the database even if one or more secondary replicas are unavailable. This mode provides lower levels of data protection but higher levels of performance.
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