VMware Stirs Virtual Controversy

VMware's goals to improve the performance of virtualized environments is drawing hoots and catcalls from at least one competitor -- and raising some knotty questions for users and developers.

VMware today made generally available the latest release of its VMware Workstation software, highlighted by the addition of a paravirtualization interface called paravirt-ops. (See VMware Unveils Workstation 6.) The software has been undergoing widespread beta testing and can now be purchased for about $189 per workstation.

Paravirtualization is a software technique developed by XenSource and implemented so far by Novell, Red Hat, and other open-source Linux OS providers. It's designed to improve the performance of virtual environments by recompiling parts of the guest operating system to create shortcuts that eliminate otherwise complex translations between OS and underlying hardware. (See Insider Eyes Virtual Desktops.)

Paravirt-ops is an interface VMware claims enables "transparent paravirtualization" by streamlining virtualization processes specifically for the Linux kernel. XenSource, VMware, IBM, and RedHat got paravirt-ops included in the latest release of the Linux kernel, version 2.6.20, which is only just starting to become available for developers.

So far, VMware is the first of the paravirt-ops proponents to offer support for the interface in a commercial product, though XenSource is said to be close to providing one, too.An alternative to paravirtualization is to recode virtualization software to tap into so-called hardware assistance in chips from Intel and AMD. This is the tack advocated by Virtual Iron and reportedly by Microsoft, which doesn't yield to messing with its kernel for any reason.

There are problems with both approaches. Paravirtualization changes the operating system kernel, which means applications using the virtual environment may not be supported by their suppliers. With hardware-assisted virtualization, which has been available from Intel and AMD for at least a year, the virtual environment itself must be recoded to work with the underlying chips.

What's more, it hasn't been proven that one technique results in better performance than the other.

Are customers faced with a choice between sticking with VMware or XenSource and paravirt-ops, hoping applications are supported; or moving to Virtual Iron in hopes of getting better performance without touching the applications?

It's not that simple. VMware, for instance, supports both, even though paravirtualization may be a tad more strategic at this point. "We've supported Intel VT for over a year in our desktop and server products," says Dan Chu, VMwares VP, Emerging Products and Markets. "Long term, you need transparent virtualization. It has to be something that improves performance across different virtualization technologies and operating systems. It has to run in both single native virtualization and non-native virtualization environments."Paravirt-ops apparently fits the bill, even though VMware supports Intel's hardware-assisted virtualization in Workstation, Player, VMware Server, and VMware Infrastructure. And going forward, paravirt-ops is likely to be just one of many software-based techniques deployed by VMware to improve virtualization.

So why is paravirt-ops showing up only in VMware Workstation 6? "We have always used Workstation as a proving ground for new technology," Chu says. No word on how or when paravirt-ops will work its way into ESX or other wares. Perhaps VMware is waiting to see how things play out.

At least one VMware competitor scoffs at the effort. "We don't believe in paravirtualization," says Alex Vasilevsky, CTO and founder of Virtual Iron. "Hardware-accelerated virtualization is the way to go... Paravirtualization is a waste of engineering cycles, completely useless."

Is one technique really better than the other? Will both survive together? Are distinctions being made along marketing instead of scientific lines? We shall see.

— Mary Jander, Site Editor, Byte and Switch