However I suspect that in many cases people will be quite disappointed when pushing it into up to date production environments. If your hardware is well utilitized, virtualization for the most part can only make things worse. I would never put a heavily loaded server in a VM.

The point here is that your two servers have to be much more powerful than each of the 25 servers. High end servers tend to be disproportionately more expensive than smaller ones. One reason are the memory modules. A 4GB module is more expensive than 2 2GB modules. I do think that you can save resources with virtualization. I just wanted to say that this is often exaggerated. Besides, 25 servers still have more redundancy than 2.

“In my experience, virtualization IMPROVES performance.”

It is possible that in some cases you experience better performance. However, in general this is not true. The virtualization software simply needs computation power.

“On point 3, this is not a disadvantage of server virtualization, it’s a management issue for not training people before throwing technology at them.”

This is not a management issue, this is a cost issue. Training people costs money. Thus it is a disadvantage of server virtualization which is often neglected.

“I think everyone in IT has accepted the fact that with new technology comes new tools, but I see this as a more pessimism than a negative about virtualization. I happen to LIKE learning the new tools and find they make my job more efficient.”

Joe, I like to learn new things, too. I think your perspective is typical for an admin. Try to imagine being a controller for some minutes, and you will see everything with different eyes.

“Point 6 – virtual server sprawl is an aspect of poor execution by IT administrators, not a disadvantage of virtualization.”

Agreed!

“Point 7 – again, it is the fault of IT administrators not virtualization technology itself for pushing virtualizaztion. If you’ve hired an administrator who puts Exchange in a virtual server, then its his fault, not VMWare of Hyper-V!”

You know what? I plan to run Exchange on a Hyper-V machine . I think the point here is just that a new complexity layer makes mistakes more likely and that means it would cost extra money.

“I find myself defending Virtualization a lot these days from folks who in general resist change.”

You won’t believe it, but I often find myself in the same role. I am a big fan of server virtualization. The advantages outweigh the disadvantages by far. However, that doesn’t mean that there are no disadvantages of server virtualization.

On point 2, you said ‘The problem is that it is almost impossible to estimate in advance how many extra resources will be needed. I know that there are capacity planning guides and tools but from my experience every piece of software behaves differently in a virtualized environment. We have applications that are quite modest as long as they run on a physical server, but when they were virtualzed their resource requirement multiplied.’
In my experience, virtualization IMPROVES performance. Why? You go from a 800 mhz dog to running on a 3ghz racehorse, of course it’s faster in a virtual environment! It reboots in 10 seconds instead of 10 minutes. And as far as estimating tools go, I have found that MAP 3.1 is extremely accurate because it literally captures performance metrics and estimates (accurately) what a consolidated server’s workload would look like.

On point 3, this is not a disadvantage of server virtualization, it’s a management issue for not training people before throwing technology at them.

On point 4 this one example is not enough for me. Especially because you never found the root cause, you can’t really say for certain that virtualization even contributed to the problem. I’ll grant you that it is perhaps an additional layer to the troubleshooting matrix, but the SSH example is a poor one because most likely this was a linux issue, not a virtualization issue.

On point 5, you seem to cite more advantages of virtualization than the one disadvantage of learning knew tools. I think everyone in IT has accepted the fact that with new technology comes new tools, but I see this as a more pessimism than a negative about virtualization. I happen to LIKE learning the new tools and find they make my job more efficient.

Point 6 – virtual server sprawl is an aspect of poor execution by IT administrators, not a disadvantage of virtualization. It’s like saying it is the car’s fault for getting the speeding ticket. Just about anything can be poorly implemented, but that isn’t the technology’s fault. Operator error =)

Point 7 – again, it is the fault of IT administrators not virtualization technology itself for pushing virtualizaztion. If you’ve hired an administrator who puts Exchange in a virtual server, then its his fault, not VMWare of Hyper-V!

I find myself defending Virtualization a lot these days from folks who in general resist change. The new reality is that most things will be virtualized because of reduced hardware and energy costs. Let’s get educated about how to implement it properly, and not be so quick to blame virtualization. Michael, all of your points would be valid if the title was perhaps ‘disadvantages of poorly trained IT staff who attempt virtualization for the first time’ or ‘mistakes to avoid with virtualization.’

Jacob, I wished I could choose VMware, too. It is just too expensive. It is true that usually only the second version of Microsoft is mature enough for prime time. But maybe one can perceive Hyper-V as the successor of Virtual Server. In our tests, Hyper-V made a good impression. Also, I don’t want to start now with ESX and then move to Hyper-V in one or two years. Changing a virtualization solution can be quite time consuming and expensive.

We have made one of our DC’s virtual, and keeps on physical. I find this configuration good, since VM-Ware gives High Availability, if one of the ESX servers goes down. And the physical DC is located out of VM-Ware to ensure that if VM-Ware should fail, there is a fail over.

We choose VM-Ware because I think that Microsoft’s solution needs to mature, as always

Yet, everything that i consider critical (Domain Controllers, Exchange, File & Print Servers, DMZ Hosts, etc.) is located on dedicated hardware.

Why? Virtualizating Exchange and Fileservers does not have any advantages (and in the case of Ex07 is even unsupported). Domain Controllers are far to critical to be used with another layer of potential goofyness.