I attended an interesting session at Citrix Synergy earlier today. It was conducted by Ron Oglesby, Chief Solution Architect of Unidesk, and the subject was why desktop virtualization has not taken off like server virtualization has. This is something I’ve wondered about myself, so I was eager to hear someone else’s view on the subject. Since a lot of the points he made could also be classified as “things to watch out for,” I thought others might also find it interesting.

First of all, it is important to recognize that “Virtual Desktop” does not equal “VDI.” (And by “VDI,” I mean turning your physical PCs into virtual machines that are running on some kind of hosting infrastructure, such as VMware, XenServer, or Hyper-V.) VMware has done a pretty good job in many cases of framing the conversation as though these terms were equivalent, because VDI is what they do, and it’s in their best interests to frame the conversation that way. Hats off to them for the degree to which they’ve accomplished that.

But VDI is just one form of desktop virtualization. The fact is that we’ve been virtualizing desktops since the debut of WinFrame a decade and a half ago. And it can be argued that XenApp is still the most cost-effective way to virtualize a desktop. I can pretty much guarantee that, on a given piece of server hardware, I can support more concurrent users with XenApp than I can by building individual virtual PCs.

But what seems to be happening in some cases is that management has seen the tremendous cost savings that have been achieved through server virtualization, so they decide that they should virtualize desktops the same way they virtualized servers, expecting that they will see the same kind of dramatic cost savings. Often, they are painfully disappointed.

Dramatic cost reduction through server virtualization is a no-brainer. You take a bunch of servers that are already in the data center, most of which are probably idling along at less than 10% processor utilization (if that), and consolidate them onto a smaller number of servers. You save space. You save power (both the power it takes to run the servers and the power it takes to cool them). You gain agility and fault tolerance through things like live motion technology. The CAPEX (capital expenditure) savings are obvious. You can probably show a positive return on investment in the first year.

Near-term CAPEX savings are almost impossible to show in a VDI project, because of the back-end infrastructure you have to put in place to host your virtual desktops. (Note that we’re talking here specifically about VDI as I defined it earlier in this post.) Your savings are primarily in ongoing operating expenses, and (according to the Burton Group in a different session I attended) it may take as long as 3 – 5 years to see a significant ROI. Beyond that, you’re talking about things that are very hard to quantify at all, such as the benefit of giving your employees the flexibility to be productive from anywhere. Great idea, difficult to quantify.

Unless you are using some kind of tool that will let you provision multiple virtual desktops from a single shared image, your storage costs are going to skyrocket, because you’re replacing cheap SATA storage on the desktop with expensive SAN storage in the data center – and a Windows 7 image with all the apps on it can easily run 30 Gb. Moreover, the way a desktop OS uses storage is completely different from the way a server uses storage. Your typical Windows server probably averages about 5 IOPS (Input/Output Operations Per Second), with a read/write ratio of 2:1 to 3:1 (more reads than writes). A Win7 system averages more like 30 IOPS, and the read/write ratio is just the opposite.

In other words, workstations aren’t servers, and they won’t behave like servers just because you move them into your data center and put them on a SAN, and therefore you can’t treat them as though they were servers. If you do, you probably won’t be happy with the result.

Finally, although IT guys love standardization, users don’t. They’re used to being able to personalize their personal computers, and they won’t easily give that up. And they definitely won’t be happy if all of the personalization they’ve done suddenly disappears when you replace their PCs with virtual desktops. Unfortunately, there is no magic wand you can wave that will transform a bunch of diverse PCs that have been highly personalized into a single shared image while still preserving all of the personalization. There are some tools that will help you with this, but you have to plan, you have to test, you have to be careful, and you need to have a roll-back plan.

So does this mean that desktop virtualization is a bad idea? No, not at all. It does mean that you need to take the time to understand your users, and come up with a desktop strategy that encompasses all of your use cases. And you need to recognize that classic VDI is probably not a “one-size-fits-all” solution for all of your users:

• Task-based workers (e.g., call centers) are probably very well served by “Hosted Shared Desktops,” a.k.a., virtual desktops running on XenApp servers.
• Remote workers may also be covered by Hosted Shared Desktops, although those who need more power, or need the flexibility of a dedicated OS, may be well served by a hosted virtual PC – traditional VDI. For example, a contract programmer may be a continent away, and may need the ability to do things that cannot be done on a shared server OS, like modifying the registry or rebooting the system, but the employer may also want the security of knowing that the code never leaves the datacenter. VDI is a perfect solution for this use case.
• Office workers may be served by hosted virtual desktops (VDI), but could also be served by streaming the PC operating system from a central shared image directly to the PC hardware on their desks. Managing that central image beats running around to all the desktops with a backpack full of CDs to do your upgrades!
• Power users who might, for example, need the power of a dedicated 3D graphics processor might be best served by streaming a central shared image to a blade PC in the datacenter, which the user then accesses via a thin-client desktop device.
• Mobile users, by definition, need to work when they’re not connected to the corporate network. This is the use case addressed by XenClient.
• In all of the cases above, having a provisioning tool that allows you to boot and run multiple systems from a single shared image is going to save you a bundle on storage.

The cool thing about XenDesktop 4 is that you can handle all of these use cases, and mix and match the best virtual desktop deployment method to each group of users, and they’re all included in your XenDesktop 4 Enterprise or Platinum license. No other vendor offers that flexibility.