You should decide on the scale and capacity of the VSA cluster and also consider some setup limitations.

Install vCenter Server on a physical host or as a virtual machine on an ESXi host that does not participate in a VSA cluster.

ESXi hosts cannot run virtual machines before creating the cluster.

vCenter Server must be installed and running before you create the VSA cluster.

If you run vCenter Server on a VSA datastore and the datastore goes offline, you might not be able to manage the VSA cluster due to the loss of access to vCenter Server and VSA Manager.

Decide on 2- or 3-member VSA cluster. You cannot add another VSA cluster member to a running VSA cluster. For example, you cannot extend a 2-member VSA cluster with another member.

Determine the capacity of the VSA cluster before installation.

vSphere Storage Appliance 1.0 does not support addition of storage to the VSA datastores and their replicas after the VSA cluster is installed.

The VSA cluster requires RAID volumes created from the physical disks. VMware recommends that you use RAID5, RAID6, or RAID10. The vSphere Storage Appliance uses RAID1 to maintain the VSA datastores’ replicas. The capacity of the VSA datastores depends on the number of physical hard disks and the RAID configuration that you use. The actual realized capacities are calculated separately for RAID5, RAID6 and RAID10. For information, see VSA Cluster Capacity.

Determine the number of virtual machines that will run in the VSA cluster.

Consider the vSphere HA admission control reservations when determining the number of virtual machines and the amount of resources that your cluster supports. vSphere HA admission control reserves 33% of all CPU and memory resources in a 3-member VSA cluster and 50% of all CPU and memory resources in a 2-member cluster. vSphere HA admission control makes the reservations to ensure that resources are available when virtual machines need to be restarted from a failed ESXi host onto a running ESXi host.

VSA datastores do not support VMX swapping. Because of this, you should reserve the configured memory of all non-VSA virtual machines that use VSA datastores so that you do not overcommit memory. For virtual machines that are not stored on the VSA datastores, you can skip this step. For more information about preventing memory overcommitment, see the VMware vSphere Storage Appliance Administration document.