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.
Licenses for Citrix XenDesktop are based on concurrent user counts, not total user counts. The Enterprise license includes XenServer, the Provisioning Server, and the Desktop Delivery Controller, covering the VM infrastructure, secure remote access, desktop provisioning, resource pooling, and live VM migration (XenMotion) when using XenServer. The cost is US$295 per concurrent user. The Platinum license is $395 per user, and includes all of the above, as well as session shadowing, performance monitoring, WAN optimization for remote-site deployments, and EasyCall, Citrix's method of connecting users and customers via the existing corporate phone services. Both editions come with XenServer, and there are presently no discounts when using another hypervisor technology.
The future is bright for VDI and, thus, for XenDesktop. Emerging technologies, such as the ability to push an OS image directly to a thin client, are quickly becoming reality. In that case, the thin client is still technically thin, but the OS executes on the client itself, not within a VM, and applications are delivered as streaming or hosted apps. This removes the need for the hypervisor, but requires a much beefier client. It would also allow for the same infrastructure to be employed for remote users running true VDI -- the user wouldn't know the difference.
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