Correction at 7:15 a.m. PST November 4: At one time, Red Hat had planned to ship an embedded KVM hypervisor based on Fedora. But the Red Hat Enterprise Virtualization Hypervisor uses the RHEL 5.4 kernel and thereby picks up the same hardware verification portfolio.
With Tuesday's release of Red Hat Enterprise Virtualization Hypervisor and Red Hat Enterprise Virtualization Manager (RHEV-M) for servers, the company has completed the first phase of a server virtualization rollout that effectively now puts KVM front and center. Red Hat released KVM commercially for the first time in September as part of Red Hat Enterprise Linux 5.4.
KVM is a server virtualization technology that Red Hat acquired when it bought Qumranet in 2008. Red Hat favors KVM over the other primary open-source hypervisor, Xen, for both business and technical reasons. (Although, as of version 5.4, Xen remains the default hypervisor for RHEL.)
The business reason is that, while Red Hat has made contributions to Xen, competitors are far more associated with the project. Novell, the owners of the only other major enterprise Linux distribution, ran especially hard with Xen early on. And Citrix, not a direct competitor but certainly a major virtualization player, bought XenSource, the commercial entity formed by Xen's creators.
From a technical perspective, Red Hat's issue is that it's hard to keep Xen and the Linux kernel in sync. Xen's a standalone hypervisor layer but it has deeply invasive hooks into the Linux kernel and, therefore, keeping the two working together takes a lot of development and testing effort. It's a bit reminiscent of how new versions of the Veritas file system had to be carefully matched to new versions of Solaris or HP-UX.
By contrast, KVM is kernel-based. This means that it is actually part and parcel of the Linux kernel rather than a quasi-independent piece of software. In part for this reason, it's KVM that is now included in the mainline Linux kernel as of version 2.6.20.
As of version 5.4, an instance of RHEL can host guest virtual machines running RHEL 5 and other operating systems including Windows Server 2008. This announcement adds Red Hat Enterprise Virtualization Hypervisor, something that is often referred to as an "embedded hypervisor." It uses the same RHEL 5.4 kernel as Red Hat's full enterprise distribution.
Embedded hypervisors have taken off more slowly than many of us expected. But all the major virtualization players offer one so Red Hat needed to as well.
From my perspective, the Red Hat Virtualization Manager is more significant. On the one hand, management is important to--indeed central to--virtualization. On the other hand, it's an area where Red Hat has lagged. CTO Brian Stevens admitted as much to me when we spoke at the company's financial analyst day last month when he said that RHEV-M "has been a huge missing ingredient."
Red Hat historically mostly focused on updating packages. This is a reflection of the broader Linux and open-source ecosystem in general. Projects like Nagios and, more recently, GroundWork notwithstanding, management doesn't play well to the strengths of open source because it's such a "high surface area" application. But Red Hat had to attack management from some angle unless it was prepared to just cede that area of differentiation and potential point of control to system makers and others.
RHEV-M is Red Hat's first step toward remedying this deficiency. It seems a necessary move especially given that KVM is likely to be used, at least initially, as part of a Red Hat software stack and therefore Red Hat pretty much has to support the tools to manage KVM if it's to gain any market traction.
That said, this is very much a first step. The initial product only manages KVM. Furthermore, the management server has to be running Windows Server 2003 which you would rightly think a rather odd decision from a company that is one of the pioneers of open source. (Apparently, this was a decision by Qumranet and Red Hat has not yet developed a version that can run on Linux.)
Red Hat has clearly prioritized getting a usable if limited product into customers' hands. They trotted out one such at their financial analyst day. Dave Costakos of Qualcomm was happy with what he saw. He told me that they wanted a Web-based interface, which RHEV Manager has. He also liked the integration with Active Directory and other directory systems, the role-based access controls, and the provisioning capabilities.
Overall, Red Hat's virtualization play remains less filled in than do the plays of others. But it's now started in a systematic way.