vSAN stretched cluster is a VMware solution that supports synchronous I/O on a local vSAN datastore on two sites that are separated geographically. This type of vSAN solution is supported on VxRail. The primary benefit of a vSAN stretched cluster is that it enables site-level failure protection with no loss of service or loss of data.

If you plan to deploy a vSAN stretched cluster on VxRail, note the following requirements:

• The VxRail nodes must be populated with the compatible disk drives so that a vSAN datastore can be configured.
• The compute and storage resources that are planned for the cluster should be doubled. It is best practice to reserve 50% of resource capacity in the cluster for failure protection.
• This cluster type requires a Witness. A Witness is a small virtual appliance that monitors the health of the stretched cluster.

• Network connectivity is required between the stretched cluster and the Witness
• An ESXi instance is required at the Witness site

• Three data center sites are required for this solution: two data center sites (Primary and Secondary) host the VxRail infrastructure, and the third site supports a witness to monitor the stretched cluster.
• A minimum of one top-of-rack switch for the VxRail nodes in the Primary site and in the Secondary site

The vSAN stretched cluster feature has strict networking guidelines, specifically for the WAN that must be adhered to for the solution to work.

Figure 26.    vSAN stretched cluster topology

More detailed information about vSAN stretched cluster and the networking requirements can be found in the Dell VxRail vSAN Stretched Cluster Planning Guide.