Citrix hits the VDI high notes

Citrix hits the VDI high notes

Citrix XenDesktop 2.0 leverages streaming applications, server virtualisation, and swift tools for a scalable and manageable virtual desktop infrastructure solution.

Streaming apps are different than hosted applications. Streaming apps execute on the VM itself, while hosted apps run from a terminal server. Terminal services are useful to VDI in a variety of ways. For instance, heavy apps that require more RAM are better off running as hosted applications, while most other apps, like the Office suite, perform better when deployed as streaming applications.

The downside of hosted apps in a VDI environment is that these apps are essentially double-hopped, since they're displayed via terminal services within an existing terminal services session.

By bringing VDI into this mix, the issue of applications that do not function in terminal-services infrastructures is essentially out of the picture. Every user is given an actual desktop system running in a VM, and recalcitrant apps can be locally installed on those VMs, rather than delivered via streaming or hosting.

Regardless of the application delivery method, access to desktops is presented through a Web interface. Thus, the user experience is identical, whether the user logs in from the company LAN or from their home PC using a Web browser.

Citrix has collected these various technologies in a single place, and offers a very simple and straightforward MMC-based management structure to make it all happen. An admin who has used Citrix products in the past will feel at home almost immediately, and even those without specific Citrix knowledge should be able to tackle the learning curve fairly quickly.

Choices, licensing, future

One issue with Citrix XenDesktop is XenServer itself. While there's no doubt that Citrix has put lots of work into XenServer, it's still not on par with VMware ESX. The selling point for XenServer in the VDI space is that it's tightly integrated with the rest of the package, but certain aspects of XenServer reduce its effectiveness in a VDI implementation – namely the lack of RAM oversubscription and RAM sharing.

If you have XenServer running on a box with 16GB of RAM and assign 512MB per VM, you will probably be able to run 25 VMs on that box. With VMware, you'll be able to get more out of the same hardware due to the RAM sharing and oversubscription. These technologies are especially useful in the VDI space, where users are generally running the same apps on every VM. This performance issue is somewhat mitigated with XenDesktop's VMware support — ostensibly, you can have your VMware ESX cake and eat it with a Citrix fork, but I didn't have a chance to test this integration to any significant degree. XenDesktop integrates with VMware's VirtualCenter to handle the behind-the-scenes VM management during normal operation.

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