More than 20 years ago, the desktop revolution swept across the land, ushering in a new paradigm of computing, taking processing away from a centralized host, and moving it to personal computers at the edge of the network. With VDI (virtual desktop infrastructure), as the saying goes, what's old is new again. Using virtualization, IT now has the ability to bring those distinct computing platforms back under one roof, while also providing for greater control and flexibility of user access.
This review of VDI solutions features the two heaviest of virtualization heavyweights. As in my comparison of entry-level VDI solutions (Kaviza VDI-in-a-box, NComputing vSpace, and Pano Logic's Pano Express), my goal was to see what it would take to deploy a complete VDI solution based on Citrix XenDesktop 5.5 and VMware View 5 for up to 50 users. During my evaluation, I found that conceptualizing the deployment was easy. XenDesktop and View are based on similar building blocks, so the overall road map for rolling out a deployment is the same. However, getting a finished installation in place took a little more thought and effort.
[ Also on InfoWorld: Download InfoWorld's Virtual Desktop Infrastructure Deep Dive special report | See which solution came out on top in InfoWorld's "Virtualization shoot-out: Citrix, Microsoft, Red Hat, and VMware" ]
Both XenDesktop and View are highly scalable, highly configurable platforms that are enterprise-grade from the word "go." Both are built to scale out to dozens of hosts and thousands of users. When compared to the Kaviza, NComputing, and Pano Logic solutions, XenDesktop and View take much more effort, knowledge, and time to get up and running. But for companies that need to be able to grow and manage a large number of virtual desktop users, XenDesktop and View are the only way to go. (Side note: Citrix purchased Kaviza in early 2011 to provide an entry-level VDI offering.)
VDI ups and downsides There are a number of advantages to virtualizing the desktop and moving it to a centralized server. First, no user data leaves the data center. All processing takes place in a controlled environment on highly redundant systems. From a security and fault-tolerance standpoint, this is a big deal. Unlike traditional desktops where data actually resides -- and can be stolen, as in the case of a laptop -- no data leaves the data center.
Another advantage is that systems management is centralized. When it comes time to patch an operating system or update an application, IT only has to do it on the master, or golden, disk image and all users receive the upgrades -- no more pushing a single update to multiple desktops across the enterprise. Perhaps one of the biggest advantages to a VDI deployment is the ability to make the user's desktop environment available to multiple end-user devices. This means a Windows 7 virtual desktop can be accessed from a Mac or Linux PC, from a thin client, from an iPad or Android tablet, or even (in a pinch) from a smartphone. The user's desktop becomes completely portable.
There are a number of considerations to take into account when building out a VDI infrastructure. The host hardware has to be pretty beefy; multiple multicore processors, scads of RAM, and plentiful disk space are absolute necessities. CPU performance and RAM are easy to come by, and while disks are cheap, choosing the correct storage system can make a huge difference on overall VDI performance. Do not scrimp on the storage system. Lots of spindles, the fastest drives you can afford, and fast I/O are paramount. SSD drives are the current speed kings, and if the budget allows, build out your online storage with them. To really scale your storage, you'll want to host virtual disks on fast SAN, NAS, or iSCSI hardware. All of the major virtualization vendors support these storage technologies.
VDI building blocks Citrix and VMware take very similar approaches to providing a VDI solution. Each vendor has its own bare metal, or Type 1, hypervisor. Each has its own connection broker to direct incoming user requests to the appropriate virtual disk image. Each provides a browser-based management tool for creating, updating, and managing the virtual desktop images and assigning the virtual machines to users. Each also provides its own remote display protocol: HDX in the case of Citrix, PCoIP in the case of VMware.
Both XenDesktop and View provide the four basic types of virtual desktops: dedicated, pooled, shared, and streamed. Dedicated desktops are stateful virtual machines assigned to specific users, allowing them to customize and preserve their personal settings from session to session. Pooled desktops -- dynamically created from a golden image when users log on, then destroyed when users log off -- are suitable for call centers or sales centers where users perform the same standard tasks and no personal user information is retained.
Shared virtual desktops, also known as session virtualization, are nothing other than Remote Desktop Services (or Terminal Services) sessions. And lastly, streamed desktops -- where client systems boot from server-based desktop images over the LAN -- combine the management benefits of VDI with the performance benefits of client-side execution.
Both XenDesktop and View also support "offline mode" -- a form of desktop virtualization that doesn't require a connection to the VDI server farm. Offline mode allows users to download the virtual desktop to their laptop and run it locally. Whenever the user is connected to the corporate network, any changes IT makes to the master image are pushed out to the local virtual machine. And depending on the personalization policy, any changes users make to their desktop are synchronized back to the data center. This mode of operation is aimed at users who are not always in communication via the Internet or corporate LAN.
Uncommon ground XenDesktop and View differ little in overall functionality. Their differences fall mainly in two areas: hypervisor support and connection protocol. Citrix built XenDesktop to run on any of the three most popular hypervisors: XenServer, vSphere, and Microsoft Hyper-V. On the other hand, View is tightly integrated with vSphere and doesn't support any other platform.
While both products support Microsoft RDP (Remote Desktop Protocol), each has its own proprietary remote access protocol. Citrix's HDX (High Definition Experience) protocol is TCP-based and includes a slew of network-aware tuning features that helps to improve the remote user experience regardless of the connection quality. VMware's PCoIP (PC over IP) is a UDP-based protocol that is also designed to provide an excellent user experience with less protocol overhead. Both HDX and PCoIP are tremendous technologies in their own right. Arguments can be made for why one is better than the other; suffice it to say that both HDX and PCoIP do a great job of providing high-quality video, audio, and complex graphics -- including Windows 7 Aero -- to the end-user's device.
Through Citrix's proprietary HDX protocol, XenDesktop delivers exceptional performance regardless of connection speed. During my testing with HDX, I connected into my virtual desktops both locally and from outside the network walls. With HDX, I didn't notice any appreciable lag in video or audio to my client. Even when viewing video on YouTube from a remote client, playback and audio quality were excellent.
Likewise, I connected to my View virtual desktops from laptops and desktops on the LAN and remotely over the Internet. Display response and audio quality were excellent with no noticeable degradation, even over untamed Internet links. Just as with Citrix HDX, YouTube playback via PCoIP was flawless. Regardless of the underlying technologies (see sidebar, "VDI shoot-out: HDX vs. PCoIP") both HDX and PCoIP provided a great end-user experience. There is always a difference between "being there" and being remote, but my experience with HDX and PCoIP was close enough to native to satisfy any user.
There are only slight differences in the number and types of endpoint devices that Citrix and VMware support. Both provide agents for Windows, Linux, iOS, and Android. Only Citrix supports Mac OS X, Solaris, HP-UX, DOS, and Symbian, and only Citrix provides a Java-based client. Both XenDesktop and View work with most popular thin clients and so-called zero clients.
XenDesktop and View are so similar in structure, deployment, capabilities, and scalability that choosing a clear winner was difficult. XenDesktop gets the nod for broader hypervisor and client support, a more flexible desktop delivery system (FlexCast), and the more extensive feature set built into HDX. This isn't to say that View is an inferior product. View is best suited for IT shops already invested in vSphere and other VMware technologies. For those shops running Citrix or Microsoft hypervisors, XenDesktop will slide right in and work fine with whatever IT already has in place. Regardless of the situation, both XenDesktop and View define what VDI is supposed to be. For full details, read the individual reviews:
VDI shoot-out: Citrix XenDesktop 5.5VDI shoot-out: VMware View 5 
This article, "VDI shoot-out: Citrix XenDesktop vs. VMware View," was originally published at InfoWorld.com. Follow the latest developments in virtualization at InfoWorld.com. For the latest business technology news, follow InfoWorld.com on Twitter.
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