In Part 1 of our VDI tutorial, we discussed virtual desktop infrastructures (VDIs) as a way in which IT departments
can deliver a full desktop image to users from virtual machines running on servers in the data center. We also outlined storage considerations and challenges, including the potential impact on back-end systems. In Part 2, we'll discuss which new products are promising to make VDI simpler.
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Virtual desktop infrastructure (VDI) technology is still a work in progress, and capacity planning and management remain among the greatest challenges confronting any IT department that elects to employ hosted virtual desktops.
"How much storage do you allocate per user? It's a very tough question to answer because what we're trying to do with hosted virtual desktops is to deliver an identical user experience [to what you] would normally get on a PC," said Mark Margevicius, a research vice president at Gartner Inc., Stamford, Conn. "If my PC that I run today in the office has a 120 GB hard drive, are users going to anticipate 120 GB of storage individually -- each and every person? That's the million-dollar question. When I speak to customers, they really struggle with this."
The latest versions of Citrix Systems Inc.'s XenDesktop and VMware Inc.'s VMware View (formerly VMware VDI) could alleviate some of the capacity issues with new features that can limit redundant data, reduce the amount of disk space needed for desktop images and provision users off the same image.
Citrix's XenDesktop 3, due this month, takes a different approach than VMware. The software can deliver hosted virtual desktops from a virtual machine in the data center, as well as streamed desktops from the same golden master images, executing them locally on any network-connected device that can run an operating system.
"It allows you to create and run hundreds or even thousands of desktops off of a single or very few images running on the provisioning servers," said Calvin Hsu, director of product marketing for Citrix's XenDesktop product group. He claims users could see up to a 90% storage reduction "because you're really storing that image only once."
The master image of the desktop is managed and handled by the provisioning server. When a user starts up a virtual desktop, key bits needed to start booting the virtual desktop are streamed from the master image over the data center network into the memory of the virtual machine, Hsu said.
"It does not have to transfer the entire 10 GB image to start working," he said. "It just transfers the bits that are needed into memory and as the user moves around and uses different parts of their desktop, it will stream those bits on demand. "
Jeff Byrne, an analyst at Hopkinton, Mass.-based Taneja Group, said VMware's Linked Clone solves the problems associated with capacity, provisioning, boot performance, and backup and recovery. If a user doesn't want to buy VMware View or Citrix's XenDesktop, they would "have" to get creative or turn to storage vendors for help. They might try thin provisioning or thin-copy technology to address some of their capacity planning woes. For backup and recovery, they might consider thin copy-on-write snapshots rather than traditional snapshots that require large amounts of space, said Byrne.
Some users might still want to tackle problems from the storage rather than server side, Byrne said, using technologies from vendors such as 3PAR Inc. (thin copy, automated provisioning, adaptive caching, space-efficient backup) and NetApp (deduplication, FlexClone gold image data store, SnapMirror for space-efficient backups). VMware's Linked Clone can be "a little tricky" to administer, according to Byrne.
"It sounds like Linked Clone is a panacea. It's not," Byrne said. "You still have to do them properly and manage them properly. There are some subtleties there."
Those who do opt for VMware's or Citrix's new technology for the initial filtering might then look to data deduplication technology from various storage vendors to further pare down the VDI storage load.
Yet another new option is IBM Corp.'s Virtual Storage Optimizer, a component of its Virtual Infrastructure Access services that aims to reduce the physical storage requirements of virtual images and the time it takes to create new desktop images. "The problem that we want to lessen on behalf of our clients is that storing virtual images requires very large amounts of expensive storage," said Jack Magoon, a global business development executive in end-user services at IBM.
But Mark Bowker, an analyst at Milford, Mass.-based Enterprise Strategy Group (ESG), remains dubious about the ROI model for VDI. He said users are still trying to figure out how to get a return.
"Take a government agency, for example, where security is a top concern. They're still willing to implement VDI for the security advantages," he said. "But if you take a typical corporate environment that doesn't have that same security challenge or mandate, maybe there isn't as much of a compelling issue to deploy VDI until the technology continues to mature."
Gartner claims an organization implementing VDI, or what it refers to as "hosted virtual desktops," can save between 2% and 12% over the TCO of a traditional PC environment, Margevicius said.
VDI-based desktops account for about 1 million units of the overall worldwide desktop market today. Predictions call for growth to 50 million units by 2012, yet that would represent roughly only 5% of the overall market, according to Margevicius.
But Taneja Group's Byrne predicted that the innovations from VMware, Citrix and other storage vendors will help make VDI more attractive to more IT organizations and continue to render the storage portion of the VDI TCO equation more reasonable.
"Any IT administrator or user who's read about the storage issues in VDI over the years, particularly up until early 2008, really needs to take a fresh new look at what's happening in this space," Byrne said.