VMware vSphere Storage Appliance (VSA)
VMware vSphere Storage Appliance (VSA) is software developed by VMware that pools disk space from ESXi hosts to provide high availability features without requiring additional storage hardware.
Certain vSphere features are unavailable without available shared storage. Because VSA mimics shared storage, users can use those features, such as vSphere HA, Fault Tolerance and vMotion.
VSA allows users to create clusters of two or three nodes. VSA takes the local storage of each node and shares it as an Network File System data store to emulate shared storage hardware.
VMware announced the end of availability for VSA effective April 1, 2014.