Sysadmin Field Notes

July 12, 2007

Is Server Virtualization the New Snake Oil? I think it depends on why they are pushing it. If it some sort of notion that you get more horsepower with a similar amount of cash, power, or cooling I'd say yes. Virtualization to save servers takes advantage of the fact that most non-prod workloads aren't really maxing out the hardware. If your prod load isn't maxing out the server, and you're not getting hardware redundancy, why would you add another server?

If you do see a gain, I'd assume you could get the same gain by optimizing your app. Maybe its cheaper/easier to just plop it on two vms, but that's a case by case thing, and by going with vms, you are almost certainly picking ip overhead.

Here's one good reason though, maybe a 3rd party component is poorly threaded. We once had two big 4 proc boxes to run a 3rd party app as part of our config, and only when we went to prod did we discover that the underlying embedded db could only run about 2simultaneous operations without bogging down. We needed lots of 1 CPU boxes, not 2 big ones. Virtualization would have let us get everything out of that hardware. So there's one useful case.

There are more though. How about forensics? See a badly behaving vm? Freeze it and put another up in its place, and your back a k own good config. Then you can analyze the copied, bad vm offline. If its a security issue, you immeditely have a bare metal copy that you can dig through as much as you want.

Patching, mainenance, deployments, rollbacks, etc. all get additional flexibility.

I await anxiously the time when the overhead is low enough to virtualize just about everything if it makes sense.