Recently, Red Hat announced that it would be dropping Xen from its Red Hat Enterprise Linux distribution starting with Red Hat Enterprise Linux 6. Red Hat has been supporting Xen for a few years and added support for KVM in Red Hat Enterprise Linux 5.4. Only KVM will be supported
Red Hat's announcement that it is dropping Xen from Red Hat Enterprise Linux is not surprising. Red Hat made it clear some time ago that KVM was its hypervisor of the future. The company said that one of the reasons Xen is being dropped is that the company was duplicating a lot of effort in maintaining two hypervisors. For example, when chip vendors add virtualization support, Red Hat had to modify both sets of software.
KVM is an upstream hypervisor, sitting in the Linux kernel, meaning that every Linux distribution ships with KVM. As the Linux kernel gets updates, KVM takes advantage of them automatically whereas Xen does not.
While there are clear advantages to using KVM over Xen, there are questions:
- What are Red Hat customers who have adopted Xen for virtualization going to do? What will customers that are running Red Hat Enterprise Linux with Xen do when they adopt Red Hat Enterprise Linux 6? Will they be migrating from Xen to KVM and are there tools available to do this?
- What about cloud providers that have adopted Red Hat Enterprise Linux with Xen as part of their virtualization infrastructure?
- Who will support Xen now that Red Hat is dropping its support? Will Xen drop by the wayside?
- What about management tools for KVM?
Red Hat says that customers should not obsess about the hypervisor, and they should not care whether they are running KVM or Xen to virtualize their data center. Red Hat customers and any cloud providers using Red Hat Enterprise Linux with Xen today have until 2014 to move to KVM or to another Linux distributor supporting Xen or to some other hypervisor. When Red Hat customers begin using Red Hat Enterprise Linux 6, they will have no support for Xen. Red Hat is providing version-to-version conversion tools for moving from Xen virtual machines to KVM virtual machines. These tools should be available later this summer in time for Red Hat Enterprise Linux 6. Red Hat does not see the conversion to be a hurdle for customers.
During the next year or two, we think that customers running Red Hat Enterprise Linux with Xen will continue to use Xen. It is stable, fast, and mature. And they have standard support from Red Hat until 2014. In terms of new Red Hat customers, we think that they will adopt KVM from the outset. It is now stable and fast. Red Hat believes that KVM has better management tools than Xen with a nice management interface.
Red Hat Enterprise Linux with KVM is already finding a number of adopters. Recently, IBM announced that its Development and Test Cloud would run Red Hat Enterprise Linux with KVM. Voddler, a Swedish on-demand movie and TV show streaming service provider, and NTT Communications are also betting that KVM will be successful in the enterprise.
Today, some cloud providers purchase Red Hat Enterprise Linux subscriptions and some deploy non-paid Red Hat Enterprise Linux. Most of these cloud providers are also using Xen. Cloud providers using Red Hat Enterprise Linux will have to transition to KVM if they move to Red Hat Enterprise Linux 6 or else seek alternative solutions. Those cloud providers who want to use a non-paid version of Red Hat Enterprise Linux have the same alternatives.
Future of Xen support
Today, Canonical (Ubuntu) and Red Hat support KVM. Novell will provide support in SUSE Linux Enterprise Server 11 SP1. It is questionable whether or not Novell can provide the level of support for KVM that it currently provides for Xen because it is a lot of engineering work. It is work that Linux distributors do not have to do if they put their efforts behind KVM. This is a good reason for Novell to also drop support for Xen. If so, who will support Xen? This leaves Citrix as the only important supporter of Xen.
John Vigeant, Senior Director of business development at Citrix, said that support for Xen is as strong as ever, especially with cloud providers and others building cloud enabling technology. He said that Citrix's investment in Xen grows as you can see with XenClient, Xen Cloud Platform, and XenServer, and Citrix certainly expects Novell and Oracle to continue to support Xen.
If Citrix cannot keep Novell (or at least Oracle) as a supporter of Xen, we believe that Xen will go by the wayside, and KVM will replace it among Linux customers, including cloud providers, both paid and non-paid. Much of the reasoning behind this is that Red Hat is by far the largest Linux vendor, and it is dropping Xen. Oracle Enterprise Linux supports Xen, but it has only 1% to 2% of the market. When the largest Linux distributors are supporting KVM and not Xen, then Xen will collapse. Amazon, the largest cloud provider using Xen today, is not likely to try to take on the task of supporting Xen, especially when KVM is available to them in Red Hat Enterprise Linux.
With few exceptions, Red Hat is rolling out the management tools for KVM, and they are based around libvirt, a virtualization library for management tools to plug into. Red Hat Enterprise Virtualization Manager for Servers is the company's flagship virtualization management product. A few other companies such as Minicom are beginning to roll out management tools around KVM. Today, we view lack of management tools as a weak point for KVM.
IT managers running Red Hat Enterprise Linux in their data centers will be confronted with making decisions around KVM and Xen. This goes for cloud providers as well. Fortunately, Red Hat will be supporting Xen on its Red Hat Enterprise Linux 5 releases until 2014 so everyone has ample time to develop strategies.
What RHEL admins should be thinking about for KVM transition
We have some things that IT managers running Red Hat Enterprise Linux should consider:
- Guest operating system support: Many involved in server virtualization have guest operating systems running on Red Hat Enterprise Linux with Xen. You should be asking yourself, What guests could I support on Red Hat Enterprise Linux with KVM? When can I support them? What is the performance level of guests running on Red Hat Enterprise Linux with KVM? Vendors such as Citrix, Novell, and Red Hat have spent considerable efforts to ensure that performance for applications running in guest operating systems on Xen is at a high level.
- Even though KVM is upstream, the bulk of the engineering and creation of an ecosystem around KVM is being done primarily by Red Hat. Will other vendors, including Canonical and Novell, get involved in this effort? Could you get locked-in to Red Hat? We think that the chances of lock-in are relatively low because KVM is available in all Linux distributions and other vendors are beginning to provide support for KVM.
- How good are the conversion tools that Red Hat is creating to move from Xen to KVM? Red Hat has indicated that they will be ready for Red Hat Enterprise Linux 6 later this year. According to Red Hat, these tools are open source and will be available for use by anyone.
- Some cloud providers, including Amazon, GoGrid, and Rackspace, have made Xen their de facto hypervisor. We believe that the longer term trend for cloud computing is "hybrid clouds." Why? Users, because of various risks associated with public clouds, are focusing on private clouds (aka on-premises clouds and internal clouds). But, IT managers will have some applications and data residing in private clouds that they will want to move to public clouds during their high-use periods. If you are doing this now or contemplating doing this, then you need to understand that conversion will be required if the cloud provider is using Red Hat Enterprise Linux with Xen (or some other Linux with Xen) and you are using KVM. This problem could disappear if KVM replaces Xen, but it could be an issue for the next two or three years.
- Look to Novell, which has been a long time supporter of Xen and which is struggling to increase its revenue and market share in the Linux, virtualization and cloud markets, to possibly try to distinguish itself from Red Hat by supporting both KVM and Xen, giving you a large amount of flexibility and extending the life of Xen (Xen 4.0 was just announced) among cloud providers.
The decisions for IT managers and cloud providers running Red Hat Enterprise Linux are not complicated:
- If you move to Red Hat Enterprise Linux 6, then you have to convert to KVM or seek an alternative solution for virtualization, which does not make much sense.
- If you want to stick with Red Hat Enterprise Linux, but don't want to migrate away from Xen in the near future, then don't upgrade to Red Hat Enterprise Linux 6. Instead, begin planning on a conversion to Red Hat Enterprise Linux 6 and KVM before 2014.
- If you are a new Red Hat customer and expect to be a Red Hat customer beyond 2014, you should adopt KVM from the outset.
- If you are using Red Hat Enterprise Linux with Xen and feel that a KVM-only move by Red Hat will lock you in to Red Hat, then work with Citrix and Novell (and Oracle if possible), encouraging them (and getting guarantees from them) to continue supporting Xen as an alternative open source hypervisor to KVM.
- Track the progress of Red Hat Enterprise Linux with KVM, but do not start conversion from Xen to KVM until Red Hat and the community has created solid conversion tools, validated performance metrics, and produced good management tools.
ABOUT THE AUTHOR: Bill Claybrook is a marketing research analyst with over 30 years of
experience in the computer industry. He is President of .New River Marketing Research and
focuses on cloud computing, virtualization technologies, and numerous aspects of Linux platforms.
He holds a Ph.D. in Computer Science.
This was first published in May 2010