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Beyond VDI: HP Client Virtualization for Citrix XenDesktop on VMware vSphere

Author:  Kirk Manzer

Title:  HP Technologist and Architect, Client Virtualization Engineering


HP has partnered with Citrix and VMware to leverage the converged capabilities of HP servers, storage and networking to develop a VDI client virtualization (CV) Reference Architecture optimized to take advantage of Citrix FlexCast within XenDesktop and VMware vSphere.


Citrix FlexCast and Personal vDisk


The Citrix FlexCast model, allows multiple ways to deliver the desktop to the end user, from using the hosted desktop capabilities of Citrix XenApp, to creating a virtual desktop that is streamed to an end user device using XenDesktop and Provisioning Services. One of the downsides to non-persistent VMs even with user virtualization is allowing a user to install customized or specific software that only they need access to. And now with XenDesktop 5.6, Citrix has added Personal vDisks (PvD). PvD from Citrix allows a non-persistent user to become a persistent user, but still use the same non-persistent base image. These users still boot from the master image maintained by IT, but have the capability to customize their environment, even install software, and have those changes remain across logins.


PvD retains the option of using a single image while allowing users to customize their desktop environment and maintain those customizations across logins, creating a persistent user but managing a single image. Adding PvD to a user means adding a SAN to store the PvD and associated differential files, preventing the user from being tied to any one specific server. The same PVS image file can be used, but the VM files, PVS write cache files and PvD are stored on a SAN. When a user logs in as part of the PvD desktop group they will be assigned a VM and PvD. By placing the files on a SAN, the user VM can be run on any server in the associated cluster. PvD uses redirection of changes made in a user’s VM to a separate vDisk attached to the user’s VM.


VMware vSphere


A key component in your HP CV Gen8 Enterprise RA solution is the virtualization software – including the VMware vSphere hypervisor. VMware vSphere provides a dynamic, reliable, and scalable virtualization platform, combined with a single set of integrated tools for managing both physical and virtual resources.

Understanding the Client Virtualization Reference Architecture

VDI is one possible implementation of the HP Client Virtualization Gen8 Reference Architecture for Citrix XenDesktop on VMware vSphere. Citrix’s FlexCast model offers several methods of delivering a desktop to a user including hosted desktops. With VDI, a desktop is created as a virtual machine. Applications and user personality are injected into the core desktop virtual machine and a brokering mechanism manages connecting end users to the VM via a connection protocol.


More than simply a virtual machine, the runtime VDI instance is the real time compilation of the end user’s data, personal settings and application settings with a core operating system instance and shared generic profile where the applications are either installed locally as a fully installed or packaged instance or streamed from outside the VM. While seemingly complex at first glance, the proper management of these individual pieces yields a far more flexible end user computing environment that is simpler to manage. This is accomplished in part by the decoupling of the user and application from the core operating system. The single OS image with few applications is easy to manage as part of an overall, comprehensive client management strategy using tools such as HP Client Automation. Once the user and application are segmented from the device, the device itself starts to matter less as well. With the right approach, an end user can receive the same experience regardless of what core compute resource they are logged onto at the moment. This also means that changing the OS layer is greatly simplified making tasks like Windows operating system migrations simpler for users who have been virtualized. Figure 1 highlights the compute device at runtime in more detail.



Figure 1: The VDI runtime instance


With Citrix XenApp, the server desktop can be configured to look like Windows 7 and served up to multiple users. All users will get the same desktop look and feel unless Citrix user personalization has been applied. The focus for XenApp is for light/task level users. For this reference architecture the XenApp servers have been virtualized rather than bare metal installation to conserve server hardware and create an easier to manage environment. XenDesktop web interface is configured to serve the hosted-shared-desktops as well as the VDI desktops.

From HP’s viewpoint, Login VSI is an excellent capacity analysis tool. When you achieve Login VSIMax the user experience/response times have reached unacceptable levels.  However, the user experience will begin to deteriorate before Login VSIMax, and HP recommends a more realistic number of users for the defined workloads. For light and medium level users a range of 60-65% is used, for the heavy level user the range is 55-60%. Table 1 shows the recommended numbers for XD VDI, Table 2 shows recommendations for XenApp.

Table 1. Recommended planning numbers by user type for VDI.


User Type



Client side flash rendering








Table 2. Recommended planning numbers by user type for virtualized XenApp.


User Type











This information and more background on the testing results/methodology are included the whitepaper, titled HP Reference Architecture for Citrix XenDesktop on VMware vSphere.


For more detail on how to utilize HP’s reference architectures to streamline your client virtualization deployments, visit our website for more options.

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