Citrix Virtualization CTO Disputes Red Hat Hypervisor Strategy

My recent blog post "Red Hat Takes Hypervisor Control Back From Citrix" appears to have elicited a response from Simon Crosby, CTO for Virtualization at Citrix. I say appears because the comment isn't verified so I can't attest for sure it was posted by Simon, so keep that in mind as you read this blog post. (Too bad NWW doesn't use Intense Debate so comments could be authenticated. I guess that's for another upcoming blog post.) I take away three main points Simon is making in his comments: 1) oVirt (a.k.a. Linux KVM) isn't really a hypervisor per se, 2) Red Hat's still involved in Xen, so they still support it, 3) oVirt/KVM have some maturing to do, but Simon's already declaring VMware, Xen and Hyper-V the viable hypervisor choices. Lets take a further look at the comment left by Simon.

The very idea that Red Hat can wrest control of anything open sourced, from any other vendor, indicates that this author fails to grasp the power of the open source movement. Red Hat is a contributor to open source, and the beauty of it is that it is free for use by anyone and that it can be developed by anyone at any time.

Mitchell's Thoughts: First, it's worth clearing something up here. I think Simon misunderstood my blog post. I was saying that Red Hat has wrested control back of its own hypervisor and virtualization strategy by coming out with oVirt rather than only relying on Xen, not that they had wrested control of an open source project. Sorry if that was confusing and wasn't clear in my original blog post.

With regard to hypervisors, it should be clearly understood that KVM is not a hypervisor, but a hosted virtualization model similar to VMware Server or Microsoft Virtual PC. The technology that KVM purports to have innovated is, to put it bluntly, well established in competitive free products. Most notably, none of those free products is used in production for enterprise workloads. Why? The hosted model of virtualization offers a simplistic way for an OS to host more OSes as virtual machines. But customers want their virtual infrastructure to be independent of their OSes -- witness the fact that VMware's revenues eclipse those of Red Hat.

Mitchell's Thoughts: FYI, it's Red Hat who is calling oVirt a hypervisor. Their own press release stated, "The hypervisor [oVirt] is based on the KVM project (". Simon, I'll let you and Red Hat debate if oVirt or KVM is a hypervisor or not. It's also interesting that Simon used VMware's revenues (not Citrix Xen's), "eclipsing those of Red Hat", as evidence customers want virtualization that's independent of the OS.

The KVM technology is an interesting, immature, Linux-based model for Linux to virtualize other guest OSes. It's convenient for Red Hat to adopt because it's just part of the Linux kernel. But Red Hat is committed to Xen, and indeed, at the current Xen Summit in Boston -- where 47 vendors, 10 universities and 15 countries were represented in a developer group of more than 175 individuals -- Red Hat engineers continued to offer contributions to Xen. Red Hat does have a very perplexing challenge though, namely the fact that KVM and Xen VMs are incompatible, and so they will find themselves offering their customers two incompatible virtualization technologies. I am not sure that this is particularly compelling as a value proposition.

Mitchell's Thoughts: I doubt Red Hat would back away from Xen anytime soon, and may never fully exit from involvement with Xen. Frankly, a lot of that depends on how Citrix manages Xen's future and maintains its integrity as an open source project. So far, so good, it seems with the steering committees that involve vendors to provide input on Xen's direction. It also depends on how oVirt does in market, and how much differentiation Red Hat can drive into the product, over Hyper-V and VMware. oVirt's new, and as you say, Simon, it's immature. oVirt has a ways to go yet. But I believe there's likely to be a crossover point where oVirt reaches a mature-enough stage that Red Hat will shift it's emphasis toward oVirt and lessen it on Xen. In the meantime, Xen's likely a big part of what Red Hat's doing in its immediate virtualization future.

Ultimately Xen and KVM will co-exist nicely as independent open source projects. Those that want a simple way for Linux to virtualize more Linux VMs will use KVM, whereas those who want a secure, minimal, Type 1 hypervisor as a component of a holistic virtualized infrastructure in which server resources are pooled into a seamless set of resources for any VM workloads, will use Xen. Customers have already voted with their feet -- VMware, XenServer and Hyper-V represent the only viable choices in the market for virtualization.

Mitchell's Thoughts: Of course it's to Citrix and Xen's advantage to discount oVirt (which I'm assuming Simon means when he refers to KVM, since that's what my blog post was about). Citrix has two horses in this virtual race: Xen and Hyper-V vs. VMware. Citrix has perfected the art of extending the Microsoft platform, and virtualization will likely be another repeat of that success story. Plus, though they are different, independently developed hypervisors, they are compatible. Hm... Imagine that. In a recent Computer World article, Simon commented that "XenServer is 100 percent compatible with Hyper-V." It sounds like Simon and Citrix are just as excited about Hyper-V's debut as Microsoft is.

Well, those were Simon's comments. I included them in their entirety, only broke them up to comment on them. I'd like to thank Simon for sharing his views on the Red Hat oVirt announcement and how he sees that impacting (or not) the Xen open source project.

Simon, you have an open invitation to join me on a podcast to dissect this topic, Xen and Citrix' virtualization products. Just contact me.

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