vSphere components together with the required hardware setup and configuration form a VSA cluster.

A VSA cluster requires the following vSphere and vSphere Storage Appliance components:

ESXi Hosts
Two or three ESXi hosts. All hosts in the cluster must have the same version of ESXi. You can also use existing hosts that have virtual machines running on their local datastores.
vCenter Server
A physical or virtual machine that runs vCenter Server and manages all ESXi hosts that participate in the VSA cluster. vCenter Server can run locally on one of the ESXi hosts in the VSA cluster. vCenter Server can also run remotely and manage multiple VSA clusters.
vSphere Web Client
The vSphere Web Client is a Web application installed on a machine with network access to your vCenter Server installation.

The client enables you to manage the VSA cluster from the VSA Manager page.

vSphere Storage Appliance
A VMware virtual appliance that runs SUSE Linux Enterprise Server 11 SP2 and a set of storage clustering services that perform the following tasks:
  • Manage the storage capacity, performance, and data redundancy for the hard disks that are installed on the ESXi hosts
  • Expose the disks of a host over the network
  • Manage hardware and software failures within the VSA cluster
  • Manage the communication between all instances of vSphere Storage Appliance, and between each vSphere Storage Appliance and the VSA Manager

Only one vSphere Storage Appliance can run on an ESXi host at a time.

VSA Manager
A vCenter Server extension (plug-in) that you install on a vCenter Server machine. After you install it, you can see the VSA Manager page in the vSphere Web Client. You can use VSA Manager to monitor, maintain, and troubleshoot a VSA cluster.
VSA Cluster Member
An ESXi host that runs a vSphere Storage Appliance as a virtual machine. This is a special type of virtual machine that is a functional member of a VSA cluster that exposes a datastore and maintains a datastore replica.
VSA Cluster Service
A service that is installed with VSA Manager on the vCenter Server computer, or separately on a variety of platforms, including Windows Server 2003, Windows Server 2008, Windows 7, Linux RH, and SLES. The service is installed by default for all configurations, but is used in a VSA cluster with two members to act as a third member in case one of the VSA cluster members fails. In such a case, the Online status of two out of three members maintains the Online status of the cluster. The service does not provide storage volumes for the VSA datastores.
Important: VSA datastores (NFS) continue operating with I/O even if the VSA cluster service stops working. However, simultaneous failure of one of the VSA cluster members and of the VSA cluster service results in failure of the VSA datastores, and the status of the cluster changes to Offline. Once this happens, the NFS datastores will show as italicized and inaccessible, and any Virtual Machines and data stored on those datastores will also be inaccessible until the issue is resolved.
VSA Cluster Leader
A vSphere Storage Appliance that reports the status of the cluster to the VSA Manager. All members of the cluster participate in an election process through which they select the leader. The leader uses the cluster IP address to communicate with the VSA Manager.
Ethernet Switches
Gigabit Ethernet and 10 Gigabit Ethernet switches provide the high-speed network backbone of the VSA cluster.