The Linux KVM hypervisor is gaining steam in the cloud computing market, with two major vendors using the virtualisation software to create cloud platforms to compete against Amazon's popular EC2 service.
IBM announced in March that its test-and-dev cloud service uses KVM (Kernel-based Virtual Machine), and now hosting company The Planet has built a cloud service using a version of KVM.
While KVM isn't on the verge of supplanting VMware, Microsoft or the open source Xen hypervisor in the enterprise, Planet officials say KVM offers numerous advantages in commercial cloud offerings.
KVM is easier for Linux developers to use than Xen because "Xen was never really integrated into Linux," says Carl Meadows, senior manager of product marketing for The Planet. "It sits outside Linux as a separate microkernel." KVM, meanwhile, "was built directly into Linux and uses Linux as the host … The KVM is much simpler and more elegant than Xen."
KVM's integration into Linux makes it easier to get patches out to customers, whereas deploying patches from a separate virtualisation software requires more legwork, he says.
Also, KVM helps The Planet give its cloud customers freedom to customize the kernel running on their virtual servers, while the portability of the software allows virtual machines to be easily migrated to physical servers and vice versa, he says.
"Since KVM operates natively, it's a lot easier for us to create a dynamic hybrid environment than it would be with Xen," Meadows says.
The Planet runs seven co-location data centers worldwide and has 20,000 customers running 15 million Web sites. More than 80% of its customers already use Linux.
But The Planet is a newcomer to the cloud computing space, which consists of virtualized server instances and on-demand storage rather than dedicated hardware. The Planet's cloud service is in public beta and is running more than 500 virtual servers on Intel Nehalem-based dual-core machines shipped by Dell.
Amazon EC2, a giant in the cloud computing market, uses Xen virtualization, but Meadows says he believes KVM will be the open source hypervisor of choice in the long term, and points to IBM's recent deployment to support his argument.
While The Planet uses KVM running on Ubuntu, IBM adopted the Red Hat-branded version of KVM. Red Hat and KVM seem to have won another endorsement from Novell, which said it will support KVM in version 11 of SUSE Linux Enterprise Server.
But Novell still supports Xen, of course, and Citrix CTO Simon Crosby writes in his blog that Novell's support of KVM is to be expected because KVM comes with the mainline Linux kernel.
Citrix, which purchased XenSource in 2007, is the key vendor in the Xen community, but Crosby acknowledges that KVM has some advantages.
"It's important to realize that for a Linux vendor, KVM significantly simplifies the engineering, testing and packaging of the distro," Crosby writes. "KVM is a driver in the kernel, whereas Xen … requires the vendor to pick a particular release of Xen and its tool stack, and then integrate that with a specific kernel.org kernel, and exhaustively test them together -- rather than just getting a pre-integrated kernel and hypervisor from kernel.org."
But ultimately, user preferences are what matter, Crosby continues. Xen wins out, he writes, in part because it offers compatibility with multiple operating systems and hypervisors.
"If the use case involves the customer buying, installing and running Linux to achieve virtualization, KVM will eventually do a fine job," Crosby writes. "If on the other hand, the user expects to deploy a virtualization platform that is entirely guest OS agnostic, using a complete virtual infrastructure platform then a type-1 hypervisor that is OS agnostic … is what they will go for."
Although Citrix has a strong partnership with Microsoft, Crosby writes that relying on an operating system vendor is problematic because "no OS vendor has yet done a good job of virtualizing its competitors' products, and indeed strategically is never likely to do so."
In the case of The Planet, the debate is less Xen-vs-KVM than it is Xen-vs.-VMware. The Planet offers a managed hosting service that uses VMware in addition to its KVM-based public cloud.
VMware is popular with customers looking to The Planet to host a private cloud because they are often running VMware internally to begin with. KVM does have many of the major features that VMware does, including live migration and RAM deduplication, Meadows says. KVM's development also moves faster than VMware's because of the open source community, but KVM is still way behind in management tools, one of the main reasons VMware is more expensive than rival virtualization software.
"KVM management tools are non-existent compared to VMware's," Meadows says.
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