What is the process of SQL Server Always On?

Question

Accepted Answer

SQL Server Always On is a high availability and disaster recovery solution that provides redundancy and failover capabilities.

SQL Server Always On is a feature in SQL Server that provides high availability and disaster recovery solutions.
It allows for automatic failover between multiple replicas to ensure minimal downtime.
There are two types of Always On configurations: Always On Failover Cluster Instances (FCI) and Always On Availability Groups (AG).
FCI provides redundancy at the instance level, while AG provides redundancy at the database level.
AG allows for multiple secondary replicas for read-only access or failover purposes.
AG requires Windows Server Failover Clustering (WSFC) for automatic failover.

Accepted Answer

SQL Server Always On Availability Groups (AGs) provide high availability and disaster recovery for SQL Server databases. Here's a breakdown of the process:

*1. Planning and Prerequisites:*

* *Windows Server Failover Clustering (WSFC):*
    * Always On AGs rely on a WSFC. This cluster provides the underlying infrastructure for failover.
    * Validate WSFC configuration, including network connectivity, storage, and quorum settings.
* *SQL Server Requirements:*
    * Ensure all SQL Server instances participating in the AG are running a supported version and edition (Enterprise Edition is typically required).
    * Enable the Always On Availability Groups feature in SQL Server Configuration Manager.
    * SQL Server instances must be domain-joined.
* *Database Requirements:*
    * Databases must be in full recovery model.
    * Take a full and transaction log backup of each database.
* *Network Configuration:*
    * Configure appropriate network settings, including static IP addresses for the WSFC and AG listeners.
    * Ensure proper firewall rules are in place.

*2. Creating the Availability Group:*

* *Using SQL Server Management Studio (SSMS) or T-SQL:*
    * Connect to the primary replica instance.
    * Launch the New Availability Group Wizard in SSMS or use the CREATE AVAILABILITY GROUP T-SQL command.
    * *Specify Availability Group Name:* Provide a unique name for the AG.
    * *Select Databases:* Choose the databases to include in the AG.
    * *Specify Replicas:*
        * Add the secondary replica instances.
        * Configure failover settings (automatic or manual).
        * Define read-only routing (optional).
        * Set data synchronization preferences (synchronous or asynchronous).
    * *Specify Endpoints:* Availability groups utilize endpoints for communication. The wizard will create them, or you can create them manually.
    * *Specify Listener:*
        * Create a virtual network name (listener) that clients use to connect to the AG.
        * Configure the listener's IP address and port.
    * *Data Synchronization:* Choose how to initially synchronize data between the primary and secondary replicas (full, join only, or skip initial synchronization).
    * *Validation:* The wizard validates the configuration.
    * *Summary and Creation:* Review the settings and create the AG.

*3. Configuring Replicas:*

* *Secondary Replica Settings:*
    * Configure read-only routing lists (if applicable).
    * Adjust failover priority.
    * Set backup preferences.
* *Data Synchronization:*
    * Monitor data synchronization status.
    * Address any synchronization issues.

*4. Configuring the Listener:*

* *Register the Listener in DNS:* Ensure the listener's name is registered in DNS.
* *Configure Client Connections:* Update client applications to connect to the listener name.

*5. Failover Testing:*

* *Perform Planned Failovers:* Test failover scenarios to ensure the AG functions correctly.
* *Monitor Failover Performance:* Analyze failover times and identify potential bottlenecks.

*6. Monitoring and Maintenance:*

* *Monitor AG Health:* Regularly monitor the health of the AG, including replica status, synchronization status, and listener availability.
* *Perform Regular Backups:* Continue to perform regular backups of the databases in the AG.
* *Apply Patches and Updates:* Apply SQL Server and Windows Server patches and updates to all replicas.
* *Disaster Recovery Testing:* Periodically test disaster recovery procedures.

*Key Components:*

* *Primary Replica:* The active SQL Server instance that hosts the primary databases.
* *Secondary Replicas:* The standby SQL Server instances that maintain copies of the primary databases.
* *Availability Group Listener:* A virtual network name that clients use to connect to the AG.
* *Windows Server Failover Cluster (WSFC):* The underlying clustering technology.
* *Endpoints:* Used for communication between replicas.
* *Data Synchronization:* The process of keeping the secondary replicas synchronized with the primary replica.

Always On AGs provide a robust solution for high availability and disaster recovery, but they require careful planning, configuration, and maintenance.

What is the process of SQL Server Always On?

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