Harnessing VMware vSAN Stretched Clusters for Business Continuity in Azure

As businesses increasingly lean on technology, the need for continuous availability of critical applications and data has become vital. The interruption of IT operations can cause substantial financial and reputational losses to an organization. Therefore, implementing a robust business continuity plan that ensures uninterrupted operation of critical applications and data, even during a disaster, is imperative.
​
One of the key technologies that support this requirement is VMware vSAN Stretched Clusters, which provide high availability and protection for mission-critical applications and data. Recently, AVS (Azure VMware Solution) support for vSAN stretched clusters has been made generally available in several Azure regions, including West Europe, UK South, Germany West Central, and Australia East.

The Power of Stretched Clusters

A stretched cluster is configured by deploying an AVS private cloud across two availability zones (AZs) within the same region, with a vSAN witness placed in a third AZ. This witness constantly monitors all hosts within the cluster, serving as a quorum in the event of a split-brain scenario.

With an even deployment of hosts within the private cloud across regions, the whole system operates as a single entity. Leveraging storage policy-based synchronous replication, data is replicated across AZs delivering a Recovery Point Objective (RPO) of zero. Thus, even if one AZ faces disruption due to an unforeseen event, the other AZ can continue operation, ensuring uninterrupted access to critical workloads.

Availability and Protection with vSAN

Each AZ is divided into a preferred and secondary vSAN fault domain. Under normal conditions, Virtual Machines (VMs) will use storage policies configured for dual site mirroring as well as local failures, residing in the preferred fault domain.

In case of a domain failure, vSAN powers off these VMs, and vSphere HA then powers on these VMs in the secondary fault domain. This flexibility allows administrators to apply a variety of different storage policies based on their specific requirements.

Integrating vSAN Stretched Clusters into Business Continuity Planning

Stretched clusters are indispensable for customers seeking business continuity, providing assurance that their operations will continue even in the face of a disaster. Industries such as finance, healthcare, and government, where the availability of critical applications and data is paramount, will particularly benefit.

The technology not only offers high availability and easy management but also constitutes an efficient solution for disaster recovery. Therefore, vSAN Stretched Clusters should be considered a critical component of any business continuity plan.

Hosts and Capacity

Currently, stretched clusters are only available for use with AV36 or AV36P, depending on the region they’re deployed in. Hosts must be deployed evenly across AZs within the region, with a minimum of 6 (3 per AZ) and a maximum of 16 (8 per AZ).

Benefits

vSAN Stretched Clusters offer numerous benefits for organizations that need to ensure the high availability and protection of their mission-critical applications and data. Here are some of the key advantages:
​

1. High Availability: The most significant benefit of vSAN Stretched Clusters is that they provide high availability for critical applications. With 99.99% uptime for applications, they offer a reliable solution for businesses that require continuous operation.
2. Disaster Recovery: Stretched clusters are an effective disaster recovery solution. If one availability zone goes down due to a natural disaster or any other unexpected event, the other availability zone can continue operating, ensuring uninterrupted access to critical workloads.
3. Zero RPO: Storage policy-based synchronous replication ensures data is replicated across availability zones, delivering a recovery point objective (RPO) of zero. This means that no data is lost in the event of a failure.
4. Fault Tolerance: With vSAN Stretched Clusters, each AZ is separated into a preferred and secondary vSAN fault domain, providing an extra layer of protection. If there's a failure in the preferred domain, the system will power off the VMs in that domain and power them on in the secondary domain.
5. Scalability: Stretched clusters offer scalability by increasing the vSAN datastore capacity when additional hosts are added to the cluster.
6. Efficiency and Cost-effectiveness: Stretched Clusters provide a highly efficient and cost-effective solution for disaster recovery and high availability. Instead of having to invest in a separate disaster recovery site, organizations can use stretched clusters to replicate data and applications across different availability zones within the same region.
7. Peace of Mind: Perhaps one of the most significant benefits is the peace of mind that comes with knowing that your critical business operations will continue even in the face of a disaster.
8. Operational Simplicity: vSAN Stretched Clusters provide an easy-to-manage solution, reducing the complexity typically associated with ensuring high availability and disaster recovery.

Stretched Cluster Limitations

Despite the numerous benefits, there are some limitations to consider:

• A new, separate, Azure subscription must be used when deploying a stretched cluster.
• Standard and stretched clusters cannot co-exist in the same private cloud.
• The type of cluster – standard or stretched – must be chosen at the time of deployment; a cluster cannot be converted after it has been deployed.
• Clusters must contain the same host type.
• Some GA features of standard clusters may not be available yet for stretched clusters.
• Scale in and scale out of a stretched cluster must be in pairs.

​The benefits of vSAN Stretched Clusters undoubtedly cement their position as an essential component of a robust business continuity plan, particularly in vital sectors such as finance, healthcare, and government where constant access to data and applications is a necessity.

Also, vSAN Stretched Clusters have established themselves as a key part of business continuity frameworks, especially in significant industries like finance, healthcare, and government where uninterrupted data and application access is essential. The extensive reach of AVS support enables an ever-increasing number of businesses to leverage this technology, enhancing their capacity to ensure the uninterrupted availability of crucial applications and data.

Despite this, it's vital to bear in mind that although stretched clusters increase protection and resilience, they don't constitute a universal solution for all failure incidents, making a solid DR strategy utterly necessary. With careful implementation and thorough planning, vSAN Stretched Clusters can form a significant pillar of your organization's business continuity strategy.