VSA : vSphere Storage Appliance
What is it?
The precursor to VSAN, the VSA enabled hosts to have software based shared storage without the need for a dedicated storage platform .
“this appliance is aimed at our SMB (Small and Mid-size Business) customers who may not be in a position to purchase a physical SAN or NAS array for their virtual infrastructure, and as a result, these customers do not have shared storage”
As of April 1, 2014. all VSA has entered end of life and can no longer be purchased.
How does it work?
The software would divide up the disk allocation in such a way that a volume from one host is mirrored on another.
The selling point is that you can use a minimal set of hardware, or even an existing one, to take advantage of the great features vSphere offered while having to forgo unneeded expenditures that a company ,may not be willing to make.
A company can use high availability and DRS with a smaller investment rather than using tens of thousands to potentially hundreds of thousands on shared storage.
VSAN is a MUCH better product than VSA.
Where VSA was aimed at small to medium business, VSAN is focused on the enterprise market, moving away from what Duncan Epping likes to call “San Huggers”.
VSAN is built into the vSphere kernel, it has SSD caching, scalable and ready for the prime time.
Here is a nice comparison thanks to vSphere blog
Vmware ended a product line that, while an interesting concept at the time, has fulfilled its need. Its features have been placed into the kernel itself, integrating the best, while adding new fatures. So VSA isnt gone in a way, just renamed. Like a lot of other Vmware products.