VMware, XenSource Join Virtualization Forces For Linux

Their original disagreement has been displaced by a commitment to work on a solution together, says Simon Crosby, CTO of XenSource, the company that builds products around Xen virtualization software. The two are trying to come up with a common approach to virtualization support in the Linux kernel.

"With the help of IBM, we made a technology breakthrough that accommodates both," Crosby said in an interview Thursday. The two companies sat down together to work through the problem during the recent Linux Symposium, held in late July in Ottawa, Canada. Jack Lo, VMware's senior director of R&D, agrees. A group got together at the Symposium "to put together an interface to the Linux kernel. There's been a lot of activity" to reach agreement, he said.

The goal is to allow different hypervisors to manage Linux virtual machines generated by a competitor's software. Hypervisors are a second generation of virtualization software that provides a more efficient way of running virtual machines on a server.

Open-source Xen, first produced in research at Cambridge University, England, is a hypervisor, as is VMware's ESX Server. Microsoft is working on a hypervisor called Viridian, due in late 2007 or 2008.

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Data center managers frequently turn to virtual machines to consolidate multiple servers on one piece of hardware. The strict software boundaries of virtual machines allow different and sometimes incompatible applications to run alongside each other on one piece of hardware, reducing the demand for new servers.

The work now under way would let hypervisors from Microsoft, VMware, and Xen work together in the same data center. Under such a scenario, it would be possible for a Xen virtual machine, trapped on a piece of failing hardware, to be automatically moved over to a VMware hypervisor on another piece of hardware.

The ability to manage failovers and do backups and recoveries would be enhanced if the Linux kernel were given one method of dealing with all hypervisors, said Carlos Montero-Luque, VP of Linux product management at Novell.

VMware and XenSource have different hypervisor designs and initially disagreed on how such a Linux kernel interface might be constructed. VMware has proposed what it calls a Virtual Machine Interface to the Linux kernel that works well with ESX Server. But Rusty Russell, a Linux kernel developer employed by IBM, "came up with a proposal in Ottawa that accommodates both Xen and ESX Server," said Crosby. Both VMware and XenSource are now collaborating on Russell's idea, called Paravirt_Ops, or paravirtual operations. The collaboration flies in the face of the alleged battling that was reported going on at the end of July. A few days after the Ottawa meeting, Greg Kroah-Hartman, a Linux kernel maintainer and employee of Novell Suse Labs, complained on July 26 of a lack of joint effort by XenSource and VMware on a combined approach to Linux virtualization support. Kroah-Hartman spoke at the O'Reilly Open Source Conference in Portland, Ore.

He couldn't be reached for further comment.

Asked if Novell agreed with Kroah-Hartman, Montero-Luque said Kroah-Hartman was speaking as an individual Linux developer, not as a Novell employee. Kroah-Hartman was followed by Oracle's Robert Shimp, who declared July 31 that Oracle "was losing patience over this issue and we are going to be pushing harder and harder on everybody to come to the table," according to reports in trade publications. Asked to comment by Information Week Wednesday, Shimp declined.

By then, posts on Slashdot by Anthony Liguori of the IBM Linux Technology Center indicated that "engineers from Xen and VMware have both been working surprisingly well on this," despite reports to the contrary. XenSource CTO Crosby said he added his own comments to Liguori's: "The VMware team should be praised for engaging in an open dialogue with the Linux kernel and Xen communities," he wrote.