Virtualization with the vSphere Storage Appliance
- By Elias Khnaser
Shared storage is one of the main enablers of enterprise features in virtualization. This component of the infrastructure makes things like vMotion, high availability and Distributed Resource Scheduler, among other features, possible. Enterprise storage, however, is also one of the most expensive components of a virtualized environment. In some cases, with smaller organizations and limited budgets, the inability to acquire shared storage is a barrier to virtualization adoption. Fortunately, vSphere 5 has a solution that addresses exactly this issue, and it's called the vSphere Storage Appliance (VSA).
Typically, physical servers or blades can be accessorized with a local disk that's sufficient in capacity and in performance but limited to a physical host, and herein lies the problem: Most virtualization enterprise features require shared disks. The VSA allows you to aggregate the local storage of two or more ESXi hosts in a cluster and present them as a shared disk to ESXi and other hosts in the cluster via Network File System (NFS). The elegance of this solution is that it extends the shared disk not only to the ESXi hosts that are contributing local storage, but also to any ESXi host in the cluster, thereby instantly enabling virtualization with enterprise features.
The way this works is by deploying a VSA to each ESXi host that will contribute local storage, which enables you to use the VSA Manager, a component loaded on vCenter, to manage the storage presentation from the ESXi hosts.
Speaking of vCenter, you should note that if you plan to use the VSA architecture as your shared storage, you can't have the vCenter virtual machine (VM) live on the datastore that's created by VSA. In this environment, vCenter will have to exist on the local storage of one of the ESXi hosts, which I'm sure isn't a big deal for most customers considering this solution. I did, however, find it amusing that vCenter is always treated differently, and I'm sure that at some point it will be supported.
Virtualization came about because of the inadequate use of physical resources, but while it did a fantastic job of consolidating physical servers, it also paved the way for the neglect of certain other resources that are just as important and just as useful, such as the local disk. Server virtualization left us with an influx of local disks on physical hosts that became significantly underutilized -- if they were used at all. The VSA amplifies the reason for doing virtualization in the first place by further taking advantage of underutilized resources such as local disks.
Now, by no means am I suggesting that you should run out and sell your current enterprise storage or that you should bypass enterprise-class storage just because VMware introduced a new feature. The VSA, while very useful, could be very difficult to scale and manage as your environment grows. Remember, the goal behind enterprise-shared storage is scalability, reliability, performance and management.
That VSA is an NFS-only solution is a bit surprising because traditionally, VMware would release its features on VMFS first and then port them over to NFS -- or at the very least it would release the features for both VMFS and NFS. VMFS is VMware's proprietary Virtual Machine File System, purpose-built to run VMs.
The VSA is a fantastic solution for small environments that can't afford enterprise-class storage but want to get into virtualization. It's also a great solution for lab environments, demo environments, test and dev environments, plus a whole slew of other use cases.
Elias Khnaser, Chief Technology Officer for Sigma Solutions, is an internationally renowned expert and thought leader in the areas of IT transformation, enterprise consumerization, virtualization and cloud computing. He is well-published, authoring and co-authoring six books, numerous training DVDs and hundreds of articles. He's a blogger and columnist, writing for Virtualization Review Magazine, InformationWeek and Forbes. He's also a frequent speaker at leading technology conferences. Elias is responsible for the technical vision at Sigma, identifying trends, innovating and developing strategies for keeping the company on the cutting edge of solutions delivery. He is also a customer-facing executive, advising clients on IT transformation, development of IT roadmaps, enterprise consumerization strategies, virtualization and cloud computing.