The architecture of a VSA cluster includes the physical servers that have local hard disks, ESXi as the operating system of the physical servers, and the vSphere Storage Appliance virtual machines that run clustering services to create volumes that are exported as the VSA datastores.

vSphere Storage Appliance supports the creation of a VSA cluster with two or three members. A vSphere Storage Appliance uses the hard disks of an ESXi host to create two volumes of the same size. It exports one of the volumes as a datastore. The other volume is a replica of the volume that is exported by another vSphere Storage Appliance from another host in the VSA cluster.

VSA Cluster with 2 ESXi Hosts
VSA cluster with 2 members

In a VSA cluster with two VSA cluster members, an additional service called VSA cluster service runs on the vCenter Server machine. The service participates as a member in the VSA cluster, but it does not provide storage. To remain online, a VSA cluster requires that more than half of the members are also online. If one instance of a vSphere Storage Appliance fails, the cluster can remain online only if the remaining VSA cluster member and the VSA cluster service are online.

A VSA cluster with 2 members has 2 VSA datastores and maintains a replica of each datastore.

A VSA cluster with 3 members has 3 VSA datastores and maintains a replica of each datastore. This configuration does not require the VSA cluster service running on the vCenter Server system.

VSA Cluster with 3 ESXi Hosts
SVA Storage Cluster with 3 Datastores