What is VSAN?
This week, VMware is set to announce the availability of their much-anticipated VSAN software-defined storage solution. While they have not made the launch official yet, it can be assumed they are announcing availability since their March 6 webinar on the topic of VSAN is being hosted by the CEO and they previously reported VSAN availability in Q1. The product has been in beta for some time now and there are a reported 10,000 downloads having already taken place; however, there still seems to be a bit of confusion about what exactly VSAN is or what it is not. To clarify, let us start by looking at what it is not.
Probably the most common misconception people make about VSAN is comparing it to EMC's ViPR or Netapp's FlexArray products. While there is similarity in the concept, and both of these are actually software-defined solutions, there is a very big difference in the implementation and what they accomplish. Without getting into too much granularity, the following image is a high-level representation of how the ViPR product is deployed.
Installed across 3 separate VMs, ViPR sits on top of the hypervisor. It then allows a nice, all-in-one management of external storage devices, including third party vendors.
This is a great solution for simplifying the management of existing storage systems in large enterprises. A typical enterprise already has several different vendors' solutions and having to manage each one separately is cumbersome. A management console like ViPR helps centralize the administration of all these different storage silos, but there is limited, if any, intelligence integrated to the applications or overall virtualized environment. So, in essence, this is still very much born out of the legacy concept covered previously--many servers to many storage systems.
Conceptually, these are both virtual appliances. They sit on top of the hypervisor and attempt to aggregate all of the storage in a virtual pool. From a software layer standpoint, it looks like this:
While this is a simplified look, it illustrates that a virtual appliance sits outside the actual hypervisor. This is important to highlight because it means that ViPR is not actually in the hypervisor itself and, thus, has limited view of what takes place there. ViPR has knowledge of the storage pools it manages, but not the overall virtualized datacenter. This is where the convergence of the software-defined datacenter and, more specifically, the introduction of VSAN separates itself.