Red Hat gets closer to releasing Enterprise Linux version 6

KVM is to Linux what Hyper-V is to Windows (and Xen is like VMware).

Red Hat released the second beta of its Enterprise Linux 6 on Wednesday and declared it on track for an unspecified release date. (I've heard rumors that it's scheduled to be available in October.) A number of features are going to make network managers happy. (You'll surely want to take Mobile IPv6 out for a spin). But the spotlight is fully on KVM virtualization, now that Xen won't be an included hypervisor option. RHEL 6 will still be supported as a guest on Xen, Red Hat says.

After talking to various experts the past few weeks, it occurred to me that KVM is to Linux what Hyper-V is to Windows Server ... which makes Xen the VMware of the Linux world.

Also see: Work underway to keep Xen support in Fedora 13

In terms of features, RHEL 6 doesn't really put Red Hat ahead of other distros, says Linux distro "superman" Brad Reeves. Reeves is senior content engineer at open source support company OpenLogic. (Note that one of the things that OpenLogic sells is support subscriptions for CentOS).

"It has been three years since the last major release, so I would say that Red Hat is playing a little bit of catchup. That said, Red Hat is the predominant distribution in data centers and enterprises, so they are catching up with small players in that market," Reeves says. "If we look at others in that arena CentOS is slightly behind, but we should be expecting a comparable release hot on the heels of Red Hat as CentOS stays in lock step with Red Hat. Ubuntu server has 'most' of the features that are planned for the Red Hat release already." (By the way, you might want to check out Reeves' article from April dubbed, Comparison of Community Linux Distributions for the Enterprise. Good stuff.)

Still there's one hot item above all others that will prod an enterprise into rolling out RHEL 6. "The compelling reasons to switch? KVM virtualization.  This would be the No.1 request for the server room and people are excited to have it built in," Reeves says.

Hmmm. Reeves' vote of confidence for KVM has come on the heels of a podcast interview I did with another Linux kernel guru, Jonathan Corbet, executive editor of, and a Linux kernel contributor. Starting at 6:59, in the podcast, we begin a discussion on Xen vs. KVM and why Corbet thinks distro developers like Red Hat really ditched Xen for KVM. Linux guru offers advice on Android tablets, Linux security and virtualization

Corbet, who once worked as an enterprise systems admin still manages the servers for his news site, and is fairly gung-ho on KVM. "A virtual client running on KVM is just another Linux process," he says. "Clients running over Xen have this whole Dom0 hypervisor setup that they have to cope with. It's a more elaborate, more complex sort of arrangement. ... In the short term you might have more luck doing things under Xen. But KVM is very much the future of Linux virtualization."

If you listened to the podcast then you might be thinking ... if the (i.e. Citrix) were to submit Xen for inclusion in the Linux kernel, wouldn't that still be a good idea? It would solve the underlying problem and users would gain a hypervisor choice bundled with their distro.

All in this together
So I went to Ian Pratt, creator of Xen and founder of, and asked:

Are there any plans to submit Xen to the Linux kernel?

"Xen is a hypervisor, Linux is a guest operating system kernel -- they're different layers of the software stack. Adding the core Xen hypervisor into the Linux code base makes no more sense than adding in XenServer or even Open Office. One of the key benefits of Xen is that it is OS independent, and does a great job of running many different kinds of guest operating system (for example Windows) rather than just being Linux focused," Pratt said.

"Of course, we want Linux to run great as a guest OS on Xen, and there are various patches that help optimize this, but they've been in upstream Linux for a couple of years and are already shipped by most distros," he said.

What do you say to the complaint by distro makers that by keeping Xen separate from the kernel, the work falls to them to bring it up to date in order to include it with their distros?

"That's a fair comment - I'm sure the OS independent nature of Xen did create a little bit more work for them. With KVM they've gone for an architecture where virtualization is implemented in a module that is added to an OS kernel (just like VMware Workstation or Microsoft Virtual PC) rather than going for a separate hypervisor. There are certainly uses for that kind of virtualization, but a true hypervisor like Xen can do a better job of security, reliability and availability, etc. -- properties that are important for cloud usage and even for desktop/laptop virtualization."

That's whay I say Xen is like VMware and KVM like Hyper-V. I'm not convinced that a hypervisor really must be separate from the operating system to best serve as a host. But with a nearly final version of RHEL 6 available to play with, you'll have a chance to see for yourself.

As for other reasons to be excited about the RHEL 6, Reeves says that new file system is one. "The ext4 filesystem, extends and expands on ext3. It is fast and efficient. A great upgrade for the filesystem. It supports larger file sizes and reduces time spent repairing the file system."

He also likes CFS. "The Completely Fair Scheduler is built into the kernel.  This will improve process scheduling across multiple core processors."

As for Mobile IPv6, the protocol has been around for years. It is supported in Cisco's latest version of IOS, but, last I heard, not in Windows 7. In this day of smartphones and the coming era of tablets, it's nice to see that protocol gaining some traction.

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