A VMware vSAN 2-node cluster on VxRail has two VxRail nodes and a witness host deployed as a virtual appliance. You can manage the 2-node VxRail cluster using either a customer-managed VCenter or a VxRail-managed VCenter.
Starting with VxRail version 7.0.410, vCenter can be installed on the VxRail 2-node cluster as part of Day 1 installation. The witness still needs to be installed on another cluster but will be added to the VxRail vSAN 2-node cluster during the Day 1 process, if it is powered on and reachable from the VxRail Manager.
A vSAN 2-node configuration is similar to a stretched-cluster configuration. If a failure occurs, the witness host is the component that provides quorum for the two data nodes. As in a stretched-cluster configuration, the requirement for one witness per cluster still applies.
Unlike in a stretched cluster, the VCenter Server and the witness host are typically in a main data center. The two vSAN data nodes are typically deployed in a remote location, even though the witness host can be deployed at the same site as the data nodes. The most common deployment for multiple 2-node clusters is to use a shared witness that is hosted in the same management cluster as a VCenter Server. This deployment optimizes the infrastructure cost by sharing the VMware vSphere licenses and the management hosts.
A vSAN 2-node configuration maintains the same high availability characteristics as a regular cluster. Each physical node is configured as a vSAN fault domain, which means that the virtual machines (VMs) can have one copy of data on each fault domain. If a node or a device fails, the VM remains accessible through the alternate replica and witness components.
When the failed node is restored, the VMware Distributed Resource Scheduler (DRS) automatically rebalances the VMs between the two nodes. DRS is not required but highly recommended. It requires a vSphere Enterprise Plus edition license or higher.