From The Bad Ideas Department: Unlimited VM Migrations

Microsoft has a Server Virtualization Tool website up that allows you to compare the costs of Hyper-V to VMware as a free service. The goal is to understand the cost of running both solutions, so that you can make an informed decision. Simply enter in your total VMs and your CPU-to-VM ratio, and viola! Pricing spits out.

This seems like a rather dubious way to get to the bottom of an environment, as my day job is helping clients do exactly this (and I don’t just ask for VM / core counts and fire off a design). However, one thing continues to catch my eye as a highlighted comparison item on the checklist: VM Migrations

In the chart, the winner is Microsoft Hyper-V’s “unlimited” value, versus VMware vSphere’s 4 (for 1GbE) and 8 (for 10GbE). Here’s an excerpt.

I’ve seen this comparison touted over and over again, and frankly, it is seems like a really Bad Idea. And it’s only one of the values I’m choosing to discuss today – there are more.

An Engineer’s Perspective

VMware has an incredibly advanced and mature migration technology in the form of vMotion. I’ve seen it evolve from a process that dropped a ping or two, to later possibly dropping a ping, to ultimately (now) being a technique used on production workloads with no impact at all. It does its job, and it does it well. The limitations imposed are there for a good reason.

I’ve seen vMotion operations saturate the majority of a 10GbE pipe for short bursts, because the goal is to not waste time moving the VM, but to move it quickly and efficiently so it’s not hanging in limbo for an extended period of time. It boggles my mind that anyone with a technical background would consider using “unlimited” as the limitation of any technology that has so much potential impact on a workload. Especially if I exercise the host workload limitation of 1024 VMs (on Hyper-V) and then try to do maintenance on that server – are all 1024 VMs going to try and squeeze into a 1GbE pipe simultaneously and expect to succeed?

Bring on the unlimited migrations!

While I do think that VMware should allow customers with advanced technical understanding to edit this field, as a host cluttered with a lot of tiny VMs (perhaps in the case of VDI) may not need to be limited to 4 or 8, I understand that this opens a can of worms from a support perspective.


I’m a big fan of Microsoft products; Exchange, SQL, and Server have all been good to me, and offer a lot of value to the business. I even understand that from a raw dollars point, Hyper-V typically has the advantage (or at least they will if these prices hold true when the products release). But this Hyper-V comparison chart is just riddled with really lame comparison points in an effort to coat one side with green boxes and the other with red boxes. Could we please stop using such blatantly silly values to compare against?