When deploying a new IT system, the four key questions are:
- What are the goals and what value is to be created?
- How do we achieve those goals?
- What type of systems should be implemented to meet the goals, and what is the required storage performance?
- Does the target system support the value that the initial goal demands?
For instance, your goal may be to reduce the total cost of ownership associated with the thousands of desktops in your enterprise. You will achieve those goals through centralized desktop management. In the process, reducing the costs associated with the needed infrastructure and the human management of that infrastructure creates value.
The current system for achieving this goal is VDI. The idea is that thousands of virtualized desktop would sit on many servers (versus thousands of laptop or desktop devices). Centralized infrastructure and standardized, large-scale management tools would then deliver the benefits. Servers are certainly powerful enough. Networks are over-provisioned. How does storage stack up as an essential IT service?
When it comes to VDI, storage capacity is not the problem: Disk capacities are getting progressively larger while clever deduplication and compression schemes are slowing the need for additional capacity. The real problem that needs to be solved is one centered on storage performance for random IO.
Random IO Demands Storage Performance
Human interaction with desktops generates random IO. Because of Web 2.0 applications, social networking, and cloud-oriented workloads, user-generated random IO is increasing progressively. For VDI to deliver on its value, a user’s experience with a virtual desktop needs to be on par with its physical laptop or desktop brethren. Therein is the rub: Disks are supplying more capacity when, in contrast, user interactions are demanding more random IO performance.
With today's legacy storage technologies, to get additional performance, you add additional disks. Each disk delivers approximately 100 IOPS. To get sufficient performance for a large-scale VDI installation - or any other IT system that generates lots of IOs like a OLTP system - lots of spinning disks have to get deployed to get to the target performance window. As such, much more storage capacity is deployed than needed; and with that comes additional costs associated with the hardware itself, software licenses, support contracts, data center floor space, power, cooling and personnel. The results are pictured below:
We could declare victory and say that we have met the goal, but what about the value that we were trying to create? To date, very few VDI implementations have been successful either because the storage subsystem lacked sufficient performance or because the expense associated with getting sufficient storage performance killed the value of the project.
In the second part of this article, I will demonstrate how an underperforming or overly expensive storage subsystem that supports a larger VDI installation (or other business critical applications) destroys real value. The analysis is shocking, or depressing, or likely both.