A virtual appliance is a virtual machine image file consisting of a pre-configured operating system environment and a single application. The purpose of a virtual appliance is to simplify delivery and operation of an application. To this end, only necessary operating system components are included.
A virtual storage appliance (VSA) is a storage controller that runs on a virtual machine(VM) to create shared storage without the cost of additional hardware.
VMware vSphere® Storage Appliance™ is a software-based shared storage solution that enables high availability and automation in vSphere without shared storage hardware. - See more at: http://www.vmware.com/in/products/vsphere-storage-appliance#sthash.hElbzmfc.dpuf