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Embedded hypervisors revisited

That embedded hypervisors for server virtualization have been slow to take off doesn't necessarily mean that the basic concept is flawed.

I noted last month that embedding the code for server virtualization directly into the hardware, something called an embedded hypervisor, hasn't taken off to any significant degree.

Rather, most IT shops continue to purchase virtualization as a third-party add-on (typically from VMware or Citrix), or they acquire it as part of Linux distribution or Microsoft Windows.

Many of the management and other services associated with virtualization are going to be added on, in any case. However, the thinking of a lot of people went, wouldn't it make sense to at least get the foundation in place as part of the server purchase, given that we're seeing more and more interoperability between the various hypervisors and the software that exploits them?

Since writing that piece, I've received a variety of interesting comments, and had some discussions with IT vendors and others I thought worth sharing.

Reader rcadona 2k commented:

Adopting a hypervisor is an active choice or, in most cases, a surrender of your hardware. Embedded hypervisors aren't just a BIOS; they require formatting your storage a particular way (VMware VMFS, Hyper-V NTFS, LVM/raw LUNs for Xen). The virtual BIOS features amongst hypervisors for the guests are not standardized, and the virtualized guest devices are not standardized. When you pick a Type-1 hypervisor, you lock yourself into another "platform."

Some good points here. We have a a bad habit in the IT industry of using the word "commodity" when we really mean things along the lines of "widely used with variants available from multiple sources" (and, therefore, relatively low-price). Hypervisors are an example of this. They all do roughly the same thing. There are a variety of suppliers. And the price for base-level hypervisors has been sliding toward zero.

But they're not commodities. For all the interoperability work that has been taking place at the management and services layer, there remain significant product differences that affect things as substantial as an IT shop's storage architecture. Some of these will go away--or at least be abstracted away--over time, but not all necessarily will.

Given that the choice of hypervisor still matters in such important ways, it's understandable that people continue to buy them primarily as an explicit component of the broader virtualization software ecosystem that depends on them.

Another feedback theme was just that we're still in the early days of virtualization. Perhaps most notably, when VMware rearchitected ESX Server to create the embedded ESXi version, not all the capabilities and features carried over. (Without going into all the details, the full ESX uses a Linux-based service console to manage the hypervisor; ESXi does away with this and is much thinner as a result. However, the current iteration of ESXi doesn't fully replicate all the capabilities provided by that console.)

However, the VMware partners that I've spoken with fully expect that upcoming ESXi versions will soon reach parity with the older ESX architecture and that this will therefore cease to be a reason to shy away from the embedded approach.

I remain skeptical that embedded, just-built-in hypervisors are going to become the norm that it once seemed they would be. If nothing else, Microsoft's Hyper-V--most likely predominantly installed as part of Windows--will tend to hold sway in Microsoft-centric environments, of which there are many.

At the same time, it's too early to write off the idea of embedding hypervisors just because the idea hasn't gained a lot of initial momentum.