You can create a stretched cluster that spans two geographic locations (or sites). Stretched clusters enable you to extend the Virtual SAN datastore across two sites to use it as stretched storage. The stretched cluster continues to function if a failure or scheduled maintenance occurs at one site.
Introduction to Stretched Clusters Stretched clusters extend the Virtual SAN cluster from a single site to two sites for a higher level of availability and intersite load balancing. Stretched clusters are typically deployed in environments where the distance between data centers is limited, such as metropolitan or campus environments.
Stretched Cluster Design Considerations Consider these guidelines when working with a Virtual SAN stretched cluster.
Best Practices for Working with Stretched Clusters When working with Virtual SAN stretched clusters, follow these recommendations for proper performance.
Network Design for Stretched Clusters All three sites in a stretched cluster communicate across the management network and across the Virtual SAN network. The VMs in both data sites communicate across a common virtual machine network.
Configure Virtual SAN Stretched Cluster Configure a Virtual SAN cluster that stretches across two geographic locations or sites.
Change the Preferred Fault Domain You can configure the secondary site as the preferred site. The current preferred site becomes the secondary site.
Replace the Witness Host You can replace the witness host for a Virtual SAN stretched cluster.
Deploying a Virtual SAN Witness Appliance Specific Virtual SAN configurations, such as a stretched cluster, require a witness host. Instead of using a dedicated physical ESXi host as a witness host, you can deploy the Virtual SAN witness appliance. The appliance is a preconfigured virtual machine that runs ESXi and is distributed as an OVA file.
Configure Network Interface for Witness Traffic Virtual SAN data traffic requires a low-latency, high-bandwidth link. Witness traffic can use a high-latency, low-bandwidth and routable link. To separate data traffic from witness traffic, you can configure a dedicated VMkernel network adapter for Virtual SAN witness traffic.
Convert a Stretched Cluster to a Standard Virtual SAN Cluster You can decommission a stretched cluster and convert it to a standard Virtual SAN cluster.