This was a good discussion presented by Dave Asprey, VP of Cloud Security, Trend Micro. While the title here says ten reasons, each reason had multiple examples, some of which overlapped, so it was really something like “27 reasons you wouldn’t want to virtualize”. Here is the official list offered by Dave with some notes I took during the discussions of each…
When you have static, predictable computing needs
If your organization is already standardized, stable and operations are under control, it may not be worth the cost, complexity and risk of forcing the move to virtualization. In most cases you are better off starting with a small, targeted group proving the technology and learning from the small scale deployment, before pushing forward to widespread implementation.
When you can’t get a virtualization friendly license
Sometimes (particularly with small vendors) running in a virtualized environment simply is not supported. You might be able to put pressure on them to provide support; if enough customers take this approach it could work. Otherwise, you can do it anyway and break some rules but to get support you’ll need to reproduce your problem on a traditionally installed instance. Some vendors still require dongles, which clearly makes for a challenge in a virtualized environment.
When it just won’t work very wellâ€¨
High I/O apps such as databases, and those with disk intensive workloads may be mitigated to some degree by using a pass-through drive instead of a virtual drive but may simply be wise to avoid entirely. Products that require hardware cards without virtualization drivers are rare but troublesome. Graphics-intensive apps can be a concern but this is an issue VM vendors have been working hard on and as such is improving. It is also worth noting that when evaluating applications that don’t work well, there may be new technologies like I/O virtualization that can help to eliminate concerns.
When time drift will hurt your apps
Virtual machines store time apart from the physical host and as the two times diverge some applications can be affected. For example, time drive would clearly impact applications like financial real-time trading applications or an industrial control system.
When you work for a cheapskateâ€¨
If you don’t have the budget to pull it off, don’t start it. Taking a half-hearted approach is very likely to be worse than whatever you have today and would not be well received by users.
When you’re already running servers at high capacityâ€¨
While the overhead required to run a virtualized environment is shrinking fast, even the 5 to 15 percent overhead it requires may be too much if your server is already working at 60 percent or so (as pushing beyond 75% is not recommended).
When you don’t have a way to manage encryption keysâ€¨
The work around for password protecting certificates on individual VMs is not recommended. The ideal solution is a policy based encryption key management solution-- which the presenter’s company Trend Micro happens to sell (but credit where credit is due, he did not push the product but simply made everyone aware of it and within this technical discussion it was not unwelcome content).
When you use clustered apps with built in failoverâ€¨
Some older, mission critical applications may have high availability features already. One example given, “Microsoft Cluster Services with a shared disk will break in private clouds that allow VMs to automatically move around”
When you want to save money on all desktops by virtualizing them
This seems to be one of the biggest misconceptions about VDI—it simply is not cheaper. You still need a client device (which still needs to be secured and managed) and you are adding significant server infrastructure, which is expensive.
When you are running virtualization platform components
For this one Dave explained that Virtualization platforms and hypervisors rely upon AD or DNS so if you virtualized AD or DNS you end up in a situation where you can’t start your virtualized environment because of a requirement it is hosting as a virtualized service. In short, you really have to keep your DNS servers on physical servers.
All these issues are being addressed as new releases come to market. While this may come across as negative, all the benefits were also highlighted and virtualization was still encouraged. The point was to get one thinking about the fact that implementing virtualization may not (and should not) mean virtualization everything.