Understanding Storage Costs for Desktop Virtualization
High storage costs could derail a virtual desktop infrastructure project. Here's a look at what you need to understand about the ROI value of your project and the implications that three storage issues could have on it.
Fri, June 17, 2011
CIO — If you are about to start considering a virtual desktop infrastructure (VDI) project, be advised: You need to really understand what your storage costs will be up front. Unexpectedly high storage costs have delayed or derailed VDI projects more than any other single issue. To avoid that problem, and accurately understand the ROI value of your project before you begin, make sure you understand the implications of these three storage issues:
Problem 1: Evolution of Your Cost/GB for Storage
When you move from physical to virtual desktops, you are at the same time moving from a distributed to a centralized storage environment. Chances are very good that most of the storage devices attached to your current physical desktops are IDE-based storage. Your centralized storage, however, will be based on enterprise-class storage, not only because you will need that to support the scalability you require, but for a number of other operational reasons that have to do with performance, high availability, recoverability, and manageability.
IDE-based storage is widely available for roughly 10 cents/GB through retail outlets like Fry's. Enterprise-class storage is going to raise the cost per GB of storage a minimum of 30x if youre looking at SATA based storage, and as much as 100x if you're looking at FC-based storage that supports critical centralized storage functionality like high performance caches, sharing, multi-path I/O, and disk-based snapshots. You can't create the centralized data store you need for VDI projects without using enterprise-class storage technology. Therefore, you will need to factor in the necessary additional costs when budgeting for your VDI storage platform.
Problem 2: How VDI Increases Your Need for Storage
As if paying a lot more per GB for your storage isn't bad enough, you are also going to need more of it. If your administrators use their experience configuring storage on physical servers to estimate their requirements in VDI environments, you will generally be surprised to find that you need to purchase 30-50 percent more storage to meet your performance requirements.
Why does this happen? Basically, the I/O patterns generated in VDI environments, where you may have 50-70 virtual desktops, each with their own individual I/O streams, running on a single physical server, end up being significantly more random and significantly more write-intensive than they are in physical environments as you write them down through the hypervisor and out to disk. Spinning disk performs at its worst in very random, very write- intensive environments, with the slowdown being worse the more random and write-intensive they are. For a given performance requirement (e.g. I/O's per second or IOPS), the storage configuration that met your needs on a dedicated application server will appear to run at least 50 percent slower in a VDI environment, and often much more. As administrators add more hardware (e.g. more disk spindles, solid state disk, etc.) to get back to their original performance target, the costs mount. You may meet your performance goals before you run out of storage budget, or you may not, but either way, you end up spending a lot more on storage than you probably originally planned.
