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High Availability and Disaster Recovery for SQL Server on Azure VMs

Ensure your critical SQL Server workloads remain accessible and resilient with robust High Availability (HA) and Disaster Recovery (DR) strategies. This section guides you through implementing and configuring these solutions for SQL Server running on Azure Virtual Machines.

Overview of HA/DR Concepts

High Availability (HA) aims to minimize downtime for applications by ensuring continuous operation. Disaster Recovery (DR) focuses on recovering data and services in the event of a major outage or disaster. For SQL Server on Azure VMs, several strategies can be employed:

  • Always On Availability Groups (AGs): Provides database-level redundancy and automatic failover.
  • Failover Cluster Instances (FCIs): Offers instance-level redundancy using Windows Server Failover Clustering.
  • Log Shipping: A simpler DR solution for recovering databases from transaction log backups.
  • Azure Site Recovery (ASR): A comprehensive DR solution that replicates VMs to a secondary Azure region.

Implementing Always On Availability Groups (AGs)

Always On Availability Groups are the recommended HA/DR solution for SQL Server on Azure VMs, offering features like readable secondaries and automatic failover.

Prerequisites:

  • At least two SQL Server virtual machines in Azure.
  • A Windows Server Failover Cluster (WSFC) configured.
  • Appropriate Azure networking configuration (e.g., Load Balancers, VNet peering).

Tutorials:

Configure Basic Availability Group

This tutorial walks you through setting up a single-node Availability Group for basic HA.

Steps:

  1. Enable the AG feature on SQL Server.
  2. Create the Availability Group in SQL Server Management Studio (SSMS).
  3. Add databases to the AG.
  4. Configure synchronization mode and failover mode.

Configure Multi-Subnet Availability Group

Learn how to configure AGs across different Azure subnets for enhanced resilience.

Considerations:

  • Ensure proper network connectivity between subnets.
  • Configure the AG listener for multi-subnet environments.

Set up Availability Group Listener

A listener provides a single point of connection for clients to access the AG, abstracting the underlying replicas.

Key Configurations:

  • Listener DNS Name
  • Listener Port
  • Listener IP Address (consider static IPs and Azure Load Balancers)

Implementing Failover Cluster Instances (FCIs)

FCIs provide instance-level redundancy. This is often used in conjunction with Shared Storage (e.g., Azure Shared Disks or Storage Spaces Direct).

Steps:

  1. Set up shared storage.
  2. Install Windows Server Failover Clustering.
  3. Install SQL Server as a Failover Cluster Instance.
  4. Configure the cluster and SQL Server resource.

FCIs are typically recommended for scenarios where database-level granularity isn't the primary requirement, or when using specific shared storage solutions.

Log Shipping for Disaster Recovery

Log shipping is a cost-effective DR solution that continuously backs up transaction logs from a primary server to one or more secondary servers.

Process:

  1. Perform a full backup and restore of the primary database on the secondary.
  2. Configure transaction log backup jobs on the primary.
  3. Configure transaction log restore jobs on the secondary.
  4. Monitor the log shipping status.

Log shipping is generally used for DR scenarios where some downtime is acceptable, and read-only access to secondary databases is not a primary requirement.

Leveraging Azure Site Recovery (ASR)

Azure Site Recovery provides a robust DR solution by replicating entire VMs to a secondary Azure region. This offers a broader scope of protection than AGs or FCIs alone.

Benefits:

  • Replicates entire VMs, not just databases.
  • Facilitates planned and unplanned failovers to a secondary region.
  • Offers a comprehensive DR strategy for your SQL Server environment.

ASR can be used to protect the VMs hosting your SQL Server instances, ensuring that in a disaster, you can bring up your entire environment in another region.

Best Practices and Considerations

  • Testing: Regularly test your failover and recovery processes.
  • Monitoring: Implement comprehensive monitoring for all HA/DR components.
  • Networking: Design your Azure network carefully to support HA/DR requirements (e.g., low latency, high bandwidth).
  • Storage: Choose appropriate Azure storage options for your needs (e.g., Premium SSD, Ultra Disk, Azure Shared Disks).
  • Patching: Plan and execute patching strategies that minimize downtime.
  • Licensing: Understand SQL Server licensing implications for HA/DR configurations.

By implementing the right combination of these HA/DR solutions, you can significantly improve the resilience and availability of your SQL Server databases running on Azure VMs.