Technically, VMware is not releasing the disk format under an open source license -- or, really, any license. According to Dan Chu, VMware's senior director of developer and ISV products, the company will release "language to make sure folks are comfortable," but the company will not require developers to accept any license terms in order to have access to the format. "We're taking it even further; you don't even have to enter into a specific open source license [to use the format]."
What the company is releasing, says Chu, is "extensive paper documentation" for the format, which describes the virtual machine environment and how it is stored. The format is already in use outside of VMware by several companies, including BMC Software, PlateSpin, Symantec, and rPath.
rPath uses the specification to create VMware-compatible images of distributions created by the rPath rBuilder. Billy Marshall, CEO of rPath, says that the company has been working with the specification for five or six months.
Chu says that having access to the format could be useful for vendors who provide patch management and update software, disaster recovery, backup software, virus scanning, and so forth.
Whether other vendors of virtualization software will be willing to standardize on VMware's disk format is an open question. Chu didn't say that any virtualization vendors had signed on to use the format, but from a technical perspective, it may not be too difficult. For example, Marshall says that the Qemu and VMware formats "aren't enormously different."
Chu says that "it really is just a disk format, the amount of complexity is not extreme.... I do think it's an easy area to converge and agree on a standard."
So far, in the last year VMware has released its free VMware Player to run guest operating systems on the desktop, as well as VMware Server, a free "entry level virtualization" product similar to VMware GSX.
It's fair to wonder whether VMware is reacting to market pressure from other vendors and projects entering the virtualization space. While VMware is the market leader, a number of other companies and open source projects have started to take aim at the virtualization market as well. VMware is now competing with SWsoft, Virtual Iron, Microsoft, the Xen and Qemu projects, and others.
From Marshall's perspective, releasing the disk format is "a natural progression" for VMware trying to keep its leadership position. "I would say there's lots of competitive technology on the horizon, and big investments being made. VMware is trying to maintain its significant leadership position. If you're not aggressive about thinking two steps ahead [of competitors] that can be lost."
Chu denies that virtualization is becoming a commodity product, however. He says that the market is becoming "not mainstream, but pervasive," and that customer expectations regarding virtualization have changed "over the past three or four years." While basic virtualization is becoming more commonplace, the surrounding technologies that make it usable for enterprise deployments are still rare.
Looking to the future
Marshall suggests that, over the long term, virtualization may "uncouple application development" from the operating system, and that having a specification for anyone to create virtual guests is a big part of that. In a post on his blog, Marshall suggested that virtualization might be the cure for "standard OS disease" (SOD).
According to Marshall, "SOD is the condition of settling for slow innovation and poor performance while shelling out extra money to make things work together because all new innovations must be filtered through the least common denominator of a 'standard OS.'
"Ultimately, widespread and high performing virtualization is the best tonic for SOD because the application provider can simply deliver to the user their application PLUS whatever fractional OS is required to run the application most effectively."
However, Marshall says it will be years before virtualization has that kind of impact. In the meantime, he says it's hard to say how developers will make use of VMware's disk format. "The whole point of putting something [like this] out is to turn it into a model where innovation can flourish with few restrictions."