Sun is overhauling its virtual desktop software with new features that reduce storage needs by creating clones of virtual machines, and let users operate multiple virtual desktops on the same client.

Sun's Virtual Desktop Infrastructure (VDI) Software version 3, the first major update in a year, is also designed to give users access to more client devices and operating systems. Sun has been selling thin client devices know as Sun Ray for a decade, but VDI can run on other thin clients, Macs and PCs, says product marketing manager Chris Kawalek.

VDI is installed on servers in the data centre, letting client devices access desktop images over the network. As of now, Sun's virtualisation software does not allow any offline desktop access.

The improvement users will be most excited about is the creation of virtual machine clones that consume virtually no disk space, Kawalek says.

"Each user's virtual machine is 8, 10, 12 gigabytes," he says. "In a lot of cases, most of that virtual machine is identical to other users' virtual machines. That's a lot of wasted disk space."

To solve the problem, Sun integrated VDI with its Open Storage technology, an open source software platform that manages any sort of industry-standard hardware, whether it was built by Sun or its competitors. Instead of storing every virtual machine in its entirety, VDI now stores only a master image and files containing the differences between that master image and each user's virtual machine. Sun is testing to determine average reductions in storage needs but doesn't have any hard figures yet, Kawalek says.

Sun, which is the subject of rumours that it is about to be acquired by IBM, is releasing VDI 3 at prices ranging from $40 (£30) to $59 per user, per year, with support.

In previous versions of VDI, Sun did not have its own hypervisor and relied entirely upon VMware on the back end to host virtual machines, while the Sun technology operated as a connection broker. In version 3, Sun is embedding a hypervisor based on its own VirtualBox technology, but customers still have the option of using VMware.

VDI 3 supports a range of operating systems, including Windows Vista, XP and 2000; OpenSolaris; and Ubuntu. Macs can be used as client devices to connect to one of the supported operating systems, but the Mac OS itself cannot be delivered through the VDI software.

Each user can now use multiple virtual desktops, Kawalek says. For example, a user might want separate desktop images for business and personal use, or a developer might want to use Windows for administrative tasks and Ubuntu for development.

Sun has still not added the capability for users to work offline, but Kawalek hints that this may be on the way. "We know that offline access is important to people. With the core products we have, we're well positioned to add that in the future," he says.

New additions in VDI 3 also include better support for Windows Active Directory; simplified installation; expanded support for VMware; integration with the Solaris ZFS file system; and built-in-support for clients that use Remote Desktop Protocol.

Up to 160 concurrent desktops can be stored on a Sun Fire x4600 server using VDI, Kawalek says. Sun has focused on offering virtual desktop performance that's nearly as good as a standard desktop. One feature allows streaming video to be decoded locally. But Kawalek acknowledges there is still room for improvement.

"It's pretty good. Whenever you're doing something over the network there is going to be some difference in quality vs. a local machine," he says. "We spent a lot of time optimising the protocol to get the experience as close as possible to that of a regular PC."