On 2nd September (right in the middle of VMware’s VMWorld Conference in San Francisco) Red Hat, the dominant Linux vendor, announced (at its own Red Hat Summit in Chicago), that with its Red Hat Enterprise Linux 5.4 release it was “Setting the Virtualization Agenda”. In another post we will look at the validity of this claim. In this post we focus on the RHEL offering itself.
The Linux Kernel Virtual Machine (KVM) has been available for some time in, for example, Ubuntu 8.0.4 LTS (Released April 2008). KVM is widely used and stable and it is high time that Red Hat who acquired KVM when they purchased Qumranet in September 2008, started to move their customers onto it – at least to remove the uncertainty in the customer base.
Red Hat has chosen to introduce a major change to its virtualization functionality in RHEL 5.4 without waiting for the next major release, RHEL 6. It is rare for vendors to make this big a change (or indeed this much noise) about a “point release”. Indeed, most of the associated tooling is not yet available, but the urgency results from the requirement to transition customers as soon as possible from the Xen hypervisor to the KVM hypervisor so as to minimize the number of customers on Xen when the tooling does arrive.
RHEL 5 has a 15 year support cycle during which Red Hat is committed to Xen support, but tooling emerging later this year will primarily target KVM and Xen customers won’t get all the benefits. That said, Red Hat claims that its existing virtualization tooling will work against both KVM and Xen, because it operates through an abstraction layer known as libvirt.
In the main, the RHEL 5.4 release is targeted at customers who have third-party or home-grown management tooling, perhaps private and public cloud providers, or even customers who are familiar with management from command scripts. The detail of the server virtualization roadmap is as follows:
- Currently Shipping: Red Hat Enterprise Linux 5.4 “Advanced Platform” includes both KVM and Xen-based integrated server and storage virtualization as well as clustering.
- Currently Shipping: Red Hat Enterprise Linux 5.4 Server includes both KVM and Xen-based integrated server.
- “Later this year”: Red Hat Enterprise Virtualization Manager for Servers: Provides centralized management and advanced capabilities for Red Hat Enterprise Linux and Microsoft Windows virtual servers.
- “later this year”: Red Hat Enterprise Virtualization Hypervisor: A bare-metal, small-footprint hypervisor based on Red Hat Enterprise Linux 5.4 and KVM.
Licensing the underlying CPU for the base O/S virtualization allows a certain number of the same version of the operating systems to be run as guests, thereby providing virtualization “for free” if guests and hypervisor are identical O/S variations.
Red Hat points out that KVM is a kernel module, whereas Xen is not, and based on their understanding of how the two codebases work (and of course how Linux politics and governance work) they never expect Xen to be a kernel module. Red Hat has undertaken a significant Beta program including both Red Hat and non-Red Hat guests and claims up to 40% performance benefits over a Xen-based version. From a support perspective it stands behind any virtualized system, in the same way as a non-virtualized system. Clearly this support would not previously been available to customers who had added KVM support to the kernel of RHEL 5.3 or earlier.
Red Hat is now fully committed to KVM, and fully in control of its development and it can now start confidently to push Linux as a hypervisor, with a view to a bare-metal version coming out later this year, most-likely to be distributed in volume through its existing OEMs in flash ROM. Customers with existing RHEL/Xen virtualizations should stay on Xen at least until Red Hat Enterprise Virtualization Manager for Servers and associated VM translation technology is released later this year. Customers looking to start new virtualization projects on a RHEL-based hypervisor should use the KVM hypervisor from now on.
Customers who are considering starting a new project and are uncommitted to a hypervisor may now consider RHEL/KVM without the uncertainty around the long-term support of Xen by Red Hat. We will discuss the Red Hat/KVM, Microsoft/Hyper-V, VMware/vSphere and Citrix/Xen competition in another post, along with the impact of Red Hat/KVM on the other Linux players.