Understanding VSAs can be simplified using a quick history lesson. Back in the day (and by this I mean really back in the day about 25 years ago) storage systems were mostly dumb machines. They were simply connected to controllers that governed all functionality. This changed when EMC introduced the Symmetrix product line in the 1990’s. Symmetrix was the first product to shift intelligence on to the actual storage system. Over time these storage arrays kept getting more and more intelligent and today have software capabilities that would only sound fictional 20 years back. Storage arrays today come built in with critical software intelligence such as local and remote replication, optimized I/O processing, cache management, resource allocation, etc. However as these storage arrays got more intelligent they also got costlier. Today depending on capacity and performance needs, a storage array can cost anywhere between $25K to $200K.
A VSA environment is not completely hardware free. We still need physical hard disks that the software runs on top of. These can either be commodity or legacy hardware and this is where cost savings come into the picture. Your environment will also need some compute power using one or more servers. Another important component in this setup is a hypervisor. A hypervisor sits on top of your dumb/old/repurposed hardware and ensures that the VSA can talk to it. Basically the hypervisor makes sure that the VSA can talk to any kind of storage disks or arrays. Currently the four prominent hypervisors in today’s market are VMware’s vSphere, Microsoft’s hyper-V, KVM (which is open source), and Citrix’s Xen.
The biggest benefit of using a VSA is the flexibility of a software only offering. Reduced costs can be advantage, however there are many elements to this and your costs will vary depending on your environment and needs. I will get deeper into this in a subsequent post. Other benefits include the ability to scale on the go- this is easier since now you are dealing with software not hardware that needs to be shipped every time your needs change, the ability to repurpose your old hardware, and the try and buy model offered by many VSAs (just like many other commercial software products you try it for a certain period of time and buy it only if you find it useful).
The biggest risk in using a VSA is that of hardware dependency. Most VSAs in the market come bundled with software support. However you are on your own when it comes to the commodity or legacy hardware you choose to implement. Any hardware failure could be catastrophic though most VSA use cases are designed to protect against this.
Currently a good number of storage companies are looking to dip their fingers in this market. Notable VSAs in the market today include offerings by traditional giants such as HP’s StoreVirtual, NetApp’s Ontap Edge, and EMC’s vVNX (a virtual instance of the VNX storage array). Startups such as StorMagic, Nexenta, and Datacore also have offerings in this market.
VSAs are still evolving and have the potential to cause some serious disruption. Keep an eye on this space!