Desktop virtualization offers great promise, but also potential problems. Cost is at the top of that list.
Most首席信息官have started considering virtual desktop infrastructure and other types ofdesktop virtualization, but only a minority has reached the deployment stage. (See related story,"As Windows 7 gains steam, VDI set to rise"。）虚拟桌面可以潜在地为用户提供更多的灵活性，使其更易于应用补丁和减少IT帮助台呼叫，但仍然有保持桌面专业人员彻夜难眠许多问题。这里有五个陷阱需要提防。（Read a primer on bare-metal desktop hypervisors.)
1. Cost
There are certainly companies that have saved money by adopting desktop virtualization, but the majority won't see any ROI for at least a few years, if ever, analysts say. IT pros trying to convince management should not use cost as the main selling point, the analyst firm Forrester Research said in findings released last year.
"The nine-month ROI that vendors might advertise for their latest and greatest technologies can actually average three or four years, according to our clients that have crunched the numbers for their hosted desktop virtualization deployments," Forrester wrote. "Why? Because the upfront infrastructure and licensing costs far outweigh the upfront benefits."
VDI projects often require investment inthin clients, and improvements to storage and network infrastructure that can make it a costly project on the front end. On the flip side, virtualizing desktops can greatly extend the life of client devices, including regular desktop PCs, lowering costs in the long run.
The biggest problem preventing enterprises from virtualizing desktops is likely cost, says Burton Group analyst Chris Wolf.
"The ROI case for virtual desktops [over three to five years] is break-even at best right now," Wolf says. "Contrary to what vendors are claiming, the ROI isn't there for a large-scale, server-hosted virtual desktop deployment."
Windows licensing costs are another complicating factor in the calculation of long-term ROI. Microsoft recentlylowered the priceof virtual desktop operating system licenses and simplified the pricing scheme, but moving to a VDI model can still be cost-prohibitive.
2. Storage
Moving desktop images and associated data from user devices to the data center creates more stress on centralizedstorage systems, particularly if a project isn't planned sufficiently.
A "huge influx of data that was stored on local machines … now needs to be stored and administered centrally" because of desktop virtualization, Gartner notes in a February 2010 report.
Storage-area network (SAN) performance was the biggest problem Humberto Duarte ran into after implementing desktop virtualization at the Universite Rennes 2, a college in France where he is IT co-director.
"Our architecture for the storage was not very good. We ran into trouble [when large numbers of users accessed the network at once]," he says.
The university, which uses VMware VDI technology on Wyse thin clients, solved the problem by spreading virtual desktop data across multiple HP SANs and upgrading to faster disks.
IT manger Dan Powers of Cox Communications in Omaha, Neb., initially tested a virtual desktop deployment with a standard SAN, but found it would have raised storage costs about 8%. "It just kills our pricing model," he says. "It doesn't make sense.
Cox investigated iSCSI and found that a Dell EqualLogic system would lower costs by 14% while improving I/O performance. While Fibre Channel-based SANs were striping data across five disks, the iSCSI system was doing so across 48 disks, and using inexpensive SATA drives, he says.
"We've got more IOPS from our EqualLogic iSCSI than from our Fibre-based products," Powers says.
3. Network
If you're a typical worker who uses Microsoft Office and not much else, "200 kilobits of network bandwidth is probably enough," Wolf says.
但对于工人需要视频流和3 d graphics rendering, "those network requirements can scale to the hundreds of megabits and that's not often discussed," Wolf says. The problem isn't caused solely by desktop virtualization software makers. Most of the servers built by IBM, HP and other hardware vendors are limited in the number of slots for graphics adapters, making it difficult to scale out, Wolf says.
Network upgrades may be necessary before implementing VDI. Cox Communications upgraded its dual core switches, IDF closet equipment and 1 Gigabit uplinks before adopting VDI. Users of virtual desktops are even more reliant on the corporate network than a typical worker, because most VDI models offer little or no offline access.
“为了让我们能够做到这一点，我们知道的前期，我们的网络必须是绝对坚固，”鲍尔斯说。“我不能运行VDI环境中，预计运行时间在那里，如果我不把努力”。
延迟仍然是桌面虚拟化的敌人，Gartner表示。“到目前为止，VMware和思杰，为行业领导者[托管虚拟桌面]，已经集中了更多‘任务工人’或‘呼叫中心’的环境中，因此，能力有限的未连接到网络上不断的用户，“Gartner表示。“在这个时候瞄准马路战士或其他移动工作人员是在‘前沿’，因为该技术目前尚未调整为离线的要求，也为管理许多不同的模板或用户场景。”
4. Multimedia support
In addition to network concerns, a lack of good multimedia support has so far prevented desktop virtualization from being useful for employees with needs beyond the usual office tools.
思杰承诺丰富的图形与虚拟桌面的HDX technology, and VMware has tried to catch up on that front by using Teradici's PCoIP protocol. Microsoft has also improved multimedia support with Remote Desktop Protocol version 7, but in general virtual desktops still don't provide as good an experience as dedicated desktops and laptops.
VMware customer Scott Lowe, CIO of Westminster College in Missouri, is a VMware customer for server virtualization, but isn't convinced PCoIP can handle the flash and other multimedia needs of students.
"They need to make sure the desktop experience closely mimics a physical desktop exp as possible," Lowe says.
In VDI deployments, "anything flash-based is terrible. Streaming audio is not good by default," Powers says. Multimedia was the first big hurdle Powers says he had to address, noting that video announcements from the Cox CEO just didn't look right on virtual desktops. Powers improved performance by using Wyse's TCX multimedia software suite.
"It's not perfect, but it took our VDI environment from being at a dead standstill to pushing it forward," he says. Cox is still relying on version 6 of RDP, "which is not the greatest," Powers says. "If I put this in the back office for some of our analysts, I don't think they would appreciate it too much."
Desktop analysts have been keeping a close eye on RDP version 7, one of the new features in Windows 7.
Previous versions of RDP do a nice job with DirectX-based applications, but don't support multimedia redirection with flash, says Eric Hanselman, CTO of LeoStream, which makes a connection broker for virtual desktops.
“RDP 7是‘足够好’的许多远程访问使用情况的协议，”沃尔夫说，在Burton集团的报告。“对Adobe Flash和3D图形扩展支持使它远远优于以前的RDP版本。”
5. User experience
This may seem obvious, but analysts and IT pros say virtual desktop projects too often ignore the user experience during planning phases.
"Where we see stumbles is when folks create small isolated islands of virtualized desktops, without thinking about what it is their users do day to day," Hanselman says.
General task workers, perhaps 40% of all users, are pretty good targets for virtual desktop projects, says Phil Grove, global director of end user services at CSC, an IT outsourcing firm. The rest will require specialized attention, or may not be candidates for a VDI deployment.
“电力用户是不是适合于锁定下来的环境。他们是一个更具挑战性的使用情况，”他说。“因为它不适合所有使用情况下，将可能永远是真实的，不是每个人都可以得到一个虚拟桌面。”
即使技术是苏nd, it may be difficult to convince users that their virtualized desktops are an acceptable alternative, says Duarte of Universite Rennes 2. IT pros need to spend some quality time with users and show them what virtual desktops can do that regular ones can't, he says. For example, users tend to be impressed when they see that when a virtual desktop has an outage, it can be restored in exactly the same state at which the connection was lost.
"Convincing administrative people to use thin clients is very hard for us, to convince them that they can do the same things that fat desktops do," Duarte says. "If the user doesn't want to use the thin clients, the project is not viable."
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