Real World Computing

You might think this is barking mad and I wouldn't disagree with you. You might have wanted to build a system architecture in which the base OS supplies services such as DNS, DHCP, file and print sharing, and then you bring up more specific services within each VM: one for Exchange Server maybe; another for SQL; then two for web services, taking the VM count to four. But no, it seems that the base OS has to be dumb. Here, is Microsoft's exact wording: "If you run all five permitted instances at the same time, the instance of the server software running in the physical operating system environment may be used only to run hardware virtualisation software and to manage and service operating system environments on the licensed server."

But what exactly is required to "manage and service operating system environments on the licensed server"? I might interpret that to include AD, DNS and DHCP, and I might also think that I need to provide file-sharing capabilities to those VMs as part of "servicing" them. This wording is as clear as mud, and it gets worse. If you use the four-VM feature of Enterprise Server then you have to "apply" the licence for that ES (Enterprise Server) to a physical machine, just as if you'd installed it on that hardware in the old days. You can have the base ES installation on the hardware, plus four VMs of ES (plus any non-Microsoft VMs - Linux, for example), or you can have VMware ESX, say, plus the four ES VMs, plus any other VMs of any other OS.

The problem comes when you have two ES licences and two boxes. Set them up, each with their own ES licence, and you're allowed four ES VMs per box: that much is straightforward. You can use tools such as VMotion (or just stop, move, start to achieve the Microsoft manual equivalent) to move any of those ES VMs onto the other machine, but - and here's the kick in the teeth - you cannot exceed the count of four ES VMs on either machine.

For the sake of clarity, I'm going to ignore non-ES VMs such as Linux from here on in. Let's say you discover that VM4 on Machine 1 needs more capacity and so you decide to move VM2 and VM3 from Machine 1 over to Machine 2, leaving you with two ES VMs on Machine 1 and six on Machine 2. You're now in violation of your licence and need to apply an extra ES licence to Machine 2, expanding its allowable VM count from four to eight! This is all a paper exercise of course, but to lawyers a licence is a licence is a licence...

Or let's imagine that Machine 1 is emitting death-rattle noises, and you need to get your four ES VMs off that box ASAP, so you transfer them to Machine 2. Strangely enough, Microsoft does allow this, as reading the documentation again yields this nugget: "You may reassign a software licence but not on a short-term basis (ie, not within 90 days of the last assignment). You may reassign a software licence sooner if you retire the licensed server due to permanent hardware failure. If you reassign a licence, the server to which you reassign the licence becomes the new licensed server for that licence."

So I can transfer the licence, but I can't transfer it back onto a new Machine 1 for 90 days! This is a summit of stupidity. None of this applies if you buy Datacenter licences, but frankly Microsoft needs to reconsider VM hosting for small enterprises and come up with some clearer and more logical solutions.

Jon Honeyball

Continued....