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Many admins wonder whether they should choose between Xen or KVM. Both offer distinct advantages, such as the ability to run multiple OSes simultaneously and gain access to network flexibility, respectively, but the decision should ultimately come down to their primary infrastructure and any interests they might have in the cloud.
The Xen hypervisor was first conceptualized by the University of Cambridge. The Linux Foundation, who assumed stewardship of the project in 2013, maintains responsibility and spearheads developments.
A Xen-based hypervisor is a Type 1 hypervisor, which helps IT administrators run multiple OSes on the same hardware and eliminates the need for extensive management due to a small management layer for managing shared resources.
Both Citrix and Oracle adopted Xen as the foundation for their virtualization products. Citrix co-opted the Xen name and used it for both of its XenServer products, plus other offerings such as XenApp and XenDesktop. However, Citrix decided to rebrand XenServer as Citrix Hypervisor to differentiate it from the open source offering.
Differentiate between KVM vs. Xen hypervisors
The Xen hypervisor relies on a microkernel design that runs on bare-metal hardware and has the ability to run on systems without virtualization extensions. This doesn't directly apply to most modern servers, but this would be an issue for older hardware.
KVM functions at the kernel or core layer of a Linux OS, which is one of the advantages touted by KVM. By being a part of the Linux kernel, KVM gets bug fixes and security updates as Linux publishes new releases.
Vendor support for Xen has primarily come from Citrix and Oracle. KVM has IBM Red Hat, as well as the combined force of the Linux kernel development team. Both admins and vendors consider this support an advantage, considering Amazon has begun to actively move away from Xen to KVM as its primary underlying hypervisor.
Infrastructure influences hypervisor choice
The choice between KVM vs. Xen hypervisor will ultimately come down to admins' primary infrastructure. Oracle and Citrix have a large customer base and push Xen as their primary hypervisor. IBM Red Hat, SUSE and Canonical support KVM as a virtualization option running on their version of Linux. On the cloud front, admins face a similar decision with Citrix and Oracle offering a Xen-based offering as opposed to Amazon and Google on KVM.
The growing popularity of hybrid and on-premises cloud offerings is also important to evaluate. If this is something admins are deciding to investigate, they must understand and consider their existing virtualization software and how well it integrates with any prospective cloud provider.
Amazon is reducing support for Xen and opting for KVM, but the vendor still maintains a good working relationship with Citrix. Choosing the right hypervisor -- and vendor -- ultimately comes down to a case-by-case basis.
From a UX perspective, admins should fully understand all options before they make any final decisions. Major cloud vendors provide both web-based and programmatic interfaces to enable flexibility for their customers.
Automation is the main way to manage any large-scale virtualization project, which requires someone to write code. Understanding those code-writing requirements and planning for them might depend more on available human resources than anything else.
A variety of factors drives admins' decision of their preferred hypervisor. For example, choosing Amazon as their cloud provider for a new project will more than likely steer them toward KVM.
If admins are Citrix or Oracle customers looking to move their system to the cloud, they will most likely look at Xen. Making a smart choice requires admins to have a good understanding of current dependencies upon specific vendors and a clear vision of where their IT projects are heading.