Versed in Virtual Desktop: Rackspace's Knowledge of Hosted Virtual Desktop


Authoredy By: 
John Engates, Rackspace CTO
Robbie Wright, Rackspace Enterprise Marketing Sr. Manager
Christopher Johnson, Rackspace Product Engineer


Distributed computing has been pervasive in it organizations for nearly two decades, but the tables are beginning to turn. Hosted Virtual desktop, also known as Virtual desktop infrastructure (Vdi), is one of the fastest growing trends in it today, partially because of the benefi ts it offers in management, access, performance and security. This whitepaper discusses Rackspace’s experience in quick deployment and hosting of virtual desktop environments.


Why use Hosted Virtual Desktop?

IT organizations both large and small have begun to push back against the complexities and pressures caused by the traditional distributed computing model in practice in most environments today. Many see the transition to Hosted Virtual Desktop as a solution to several of the problems in their desktop computing environment. Gartner defines Hosted Virtual desktop as “a technology providing mechanisms for centralizing a thick-client desktop PC without the need to re-engineer applications for centralized execution.”(1) 

According to a survey by Gartner, the top driver for the migration to a virtual desktop environment is a desire for improvement in business agility.(2) When deployed correctly, desktop virtualization provides greater flexibility in deployment, allows for simplified image management, facilitates greater systems management capabilities and promotes mobility – without compromising security. Additionally, hosted virtual desktop solutions can better enable compliance with both government regulations like Sarbanes-Oxley and HIPAA as well as software licensing agreements.

While this technology offers some excellent benefits, careful consideration of the solution is imperative for successful implementation. Significant expertise is necessary to understand all of the variables that might come into play in an organization.



Several components are required to effectively implement a Hosted Virtual Desktop solution:

1) Virtualization software to serve as a host for the individual desktops

2) Brokering or session management software to facilitate the connection between users and their desktops

3) Management tools for the overall virtual desktop environment

4) P hysical infrastructure to facilitate the required service level agreement (SLA) and performance of the solution

5) A hosting strategy to determine what hosting solution provides the greatest value to the organization

Consideration 1: Virtualization Platform

Multiple virtualization platforms can be used for desktop virtualization including Microsoft® Hyper-V™, VMware® ESX™, Citrix® XenServer™ and others. The hypervisor does not significantly impact end-user experience, and thus, should be selected based on the needs and existing expertise of the IT department. With a growing landscape of hypervisor-agnostic orchestration and management tools, the implications of choosing the “wrong” hypervisor are becoming less pronounced, but this remains an important decision when considering how an environment will scale. For the purpose of this paper, we will focus on Citrix XenServer.

XenServer is an enterprise-class server virtualization platform built on the open-source Xen hypervisor for the management of Windows® and Linux virtual machines. Rackspace has chosen XenServer for the Hosted Virtual Desktop reference architectures included later in this whitepaper, in part, because of Citrix’s deep involvement with the open-source community. Citrix has made great strides toward integration of Xen technology with the open-source OpenStack cloud orchestration and management platform that Rackspace believes will result in significant efficiencies in the virtual desktop market in the future.

ConsIderation 2: Brokering/Session Management Software

Brokering/session management software provides the infrastructure necessary to facilitate the user sessions in a Hosted Virtual Desktop environment. there are several building blocks of this component:

1) The Web Interface uses a Java-based front end to provide the user interface. High availability is usually built into this layer through the use of redundant web interface servers, providing end users seamless access to their virtual desktop, even in the event of a web interface hardware failure.

2) The Desktop Delivery Controller is installed on servers in the data center and is responsible for user authentication, management of the assembly of users’ virtual desktop environments and brokering
connections between users and their virtual desktops. it controls the state of the desktops, starting and stopping them based on demand and administrative configuration. it also includes profile management, in some editions, to manage user personalization settings in virtualized or physical windows environments.

3) Citrix Provisioning Services creates and provisions virtual desktops from a single desktop image on demand, optimizing storage utilization and providing a pristine virtual desktop to each user every time they
log on. desktop provisioning also simplifi es desktop images, provides the best fl exibility and offers fewer points of desktop management for both applications and desktops.

Possibly the most diffi cult part of architecting a Hosted Virtual Desktop environment is understanding user requirements.

To assist in this, Rackspace has identified four common user profiles:


Task User – PC users who perform well-defi ned tasks, use few applications and have limited requirements from their PCs

Knowledge User – Typically attend meetings, visit branch offi ces, work from home and even coffee shops; these “anywhere workers” expect access to all of the same applications and data wherever they are

Power User – PC users who run resource-intensive applications

Office User – PC users who run primarily an office suite of productivity applications


Classifying users into one of these profiles can provide organizations a great head start in sizing their Hosted Virtual desktop solution. Once users are classified, the it organization can rightsize the resources provisioned for virtual desktops in each profile. This should primarily involve determining, for each virtual desktop, the number of virtual CPUs, amount of memory, storage space, input/output operations per second (iops) and bandwidth required to perform optimally.

Citrix Xendesktop™ is a lightweight, universal virtual desktop client that facilitates each of these user profi les. It provides a rich, high-defi nition desktop with full streaming audio and video. Each profile can be delivered as a streamed desktop or a persistent desktop. Streamed desktops are built on the fly and torn down at the end of each session, and therefore do not retain any applications not built into the streamed image between sessions. In contrast, persistent desktops run like regular virtual machines and remain in existence after the end of the session. Persistent desktops are typically assigned to a single person and retain any added applications from session to session.

Citrix Xenapp™ provides a framework for streamlining application delivery by streaming windows applications through a remote desktop session. It can be embedded in Xendesktop or run outside of the desktop itself. One of the major benefits of delivering applications in this fashion is ease of deployment. Xenapp allows it organizations to deploy a new application, or patch or upgrade an existing application just once for the entire organization, instead of once for every desktop or virtual machine in an environment.

Consideration 3: Systems Management

Systems management is another key consideration in a Hosted Virtual Desktop environment. As with any virtualized environment, a number of services are required for proper operation and management including an
Active Directory domain, a domain controller, a Microsoft SQL database, a Dynamic Host Configuration Protocol (DHCP) server, a Domain Name Services (DNS) server, a Network Time Protocol (NTP) server and several administration tools. As much has been written on these topics in other virtualization documentation, we will focus briefly on the systems management tools specific to a Hosted Virtual Desktop environment,
and specifically those tools in the enclosed reference architectures.

Citrix XenCenter™ provides the management layer for all Xen servers.This tool manages the virtualization layer of the server hardware and handles tasks like live migrations and performance monitoring and hardware utilization within the virtualized environment.

Desktop Director™ is the web-based operations console for XenDesktop. It is designed to simplify the provisioning and delivery of virtual desktops that reside in an environment as well as facilitating all of the day-to-day management functions from a single pane of glass.

Finally, Citrix EdgeSight™ provides a comprehensive agent-based monitoring system used to track system resources of all the components of the Hosted Virtual Desktop solution. It supports alarm thresholds, event response and historical reporting.

Consideration 4: Physical Infrastructure

Choosing the correct physical infrastructure to support a Hosted Virtual Desktop environment is critical to its acceptance and long-term viability in an organization. Undersizing components that compromise the availability or the performance of a virtualized desktop will lead to poor user experience and lost productivity. Therefore, it is necessary to scope the appropriate computing resources (processor, memory, networking, storage, etc.) to support the environment.

Advances in virtualization technology have made server hardware practically a commodity. For these reference architectures, Rackspace chose Dell™ R810 servers because of the availability of Intel® Octa-Core
Xeon® processors that enable optimal desktop density. Best practices recommend five virtual desktops per CPU core, in this case allowing 100-150 desktops per physical server.

Networking is another important consideration as part of physical infrastructure for a Hosted Virtual Desktop solution. If there is a single point of failure in the network, users cannot access their virtual desktops, resulting in lost productivity and dissatisfied users. Therefore, high availability (n+1) and the best possible service level agreements are required in the networking layer at the firewall, network load balancer and switching levels. In addition, better performance can be expected when Hosted Virtual Desktop is deployed closer in proximity to other hosted applications. With a growing number of applications being served in the cloud or through a Software-as-a-Service model, the logical deployment location to reduce network latency is often with a cloud provider. We will examine this in more detail shortly.

Other networking considerations should be around WAN optimization and secure access to virtual infrastructure. Citrix’s NetScaler™ can handle both of these tasks by providing virtual private network (VPN) access for users and using advanced algorithms for WAN optimization. Alternatively, the same effect could be accomplished by using an F5® BIG-IP® device that provides SSL VPN as well as advanced load balancing functionality.

In this case, a separate WAN optimization solution like those from Riverbed® or Brocade®, if desired, would be necessary. However, one of the simplest ways to accelerate performance by reducing latency is using Akamai® IP Application Accelerator. This technology helps to optimize the paths that data takes across the Internet based on a number of factors, often routing around congestion or outages that would reduce performance. It also can put end users’ data physically closer to them by leveraging Akamai’s vast Content Delivery Network (CDN).

Storage environments must be architected to accommodate frequently recurring events with high input/output (I/O) demands, known as “I/O storms.” I/O storms can include events like logon, logoff, boot, shutdown, antivirus scans and application patches. Typically, a virtualized desktop will require 14-24 IOPS under normal workload, but during these events, these demands can increase fivefold. Storage requirements for the average virtual desktop usually include 40-45 gigabytes (GB) of vDisk storage (for the desktop itself), 20-40 GB of user and profile storage, and 5 GB of write-cache storage. If the storage environment is not scoped and implemented correctly, users will experience greatly degraded performance during these periods.

Rackspace and NetApp® have partnered to design a storage solution suited to handle I/O storms while avoiding costly over-provisioning of storage resources. Flash cache cards in the NetApp array help achieve the IOPS needed to support an enterprise Hosted Virtual Desktop solution. Rackspace also uses NetApp’s primary storage deduplication technology, allowing organizations to avoid storing duplicate data like desktop images, significantly reducing storage requirements. Other NetApp technologies in use in the Rackspace solution include Link Aggregation Control Protocol (LACP) channel bonding (to achieve 2 GB links) and RAID-DP for economical fault tolerance.


Consideration 5: Hosting

Finally, organizations must determine the best hosting solution for their virtual desktop solution: whether to host internally or externally. While many host this application internally in their own data centers, a growing number are choosing external managed hosting solutions in order to reduce the IT overhead required to manage a virtual desktop environment and to leverage benefits in flexibility and performance that may be realized in an external data center. Security concerns surrounding external hosting of a virtual desktop solution can be mitigated with a correctly architected environment.

Typically, a hosted environment provides for faster deployment, cutting months or even years off of the deployment time of internal IT and/or a large IT outsourcing firm. If hosting at an external data center, the primary consideration should be whether the organization desires to manage the physical equipment (pure colocation) or if they prefer to have someone else take care of physical layer issues (managed colocation).


Experience in Action: Deploying Hosted Virtual Desktop for a Multi-billion Dollar Manufacturer

A large consumer packaged goods manufacturer had been outsourcing with a large IT firm to implement a virtual desktop solution. However, after 18 months of continuous work, their IT firm was unable to deploy a production-ready solution. Citrix recommended that this company contact Rackspace as an alternative to accelerate the solution. Rackspace worked with a host of companies to architect and deploy a solution to full production within just two months.


Rackspace provides infrastructure management services up to the physical device level for Hosted Virtual Desktop solutions, allowing its customers to avoid time-consuming trips to a remote data center to deal with physical layer issues like hardware failures. Rackspace works with its customers to enlist channel partners to provide broader services like end user help desk and application support.

Because of the growing number of web-based applications, there is often a performance advantage of deploying in an external data center because of decreased latency between these applications and Hosted Virtual Desktop environments. Rackspace even has the capability, with its Rackconnect™ hybrid computing solution, to provide seamless, direct connections between dedicated Hosted Virtual desktop infrastructure and applications running in Rackspace’s public cloud, providing its customers with the optimal mix of platforms to enable their client computing environment.

Rackspace provides solutions with a 100% network availability service level agreement (SLA).(3) To enable networking high availability, Rackspace provides options for redundant firewalls, high availability load balancers and redundant switching.

To enable disaster recovery, hosting providers can provide geographic redundancy more easily than in-house solutions. For example, because of Rackspace’s globally distributed data centers, it can provide a primary Hosted Virtual desktop solution in one data center with data replication to other sites all over the world without a signifi cant capital investment. This global footprint can also be leveraged to place Hosted Virtual Desktop resources physically closer to end users, reducing latency.


Rackspace has extensive experience and expertise in dedicated and cloud hosting environments. Rackspace enterprise customers will have the advantage of an implementation team that is engaged before contract signing to assist in providing a seamless transition from sales into support. this team deploys the customer’s environment, staying with them through deployment and transitioning to the permanent account team. They act as the single point of contact for any customer need during an implementation process. these and other aspects of Rackspace’s solution can greatly expedite deployment of a Hosted Virtual desktop solution.

Further, Rackspace has teamed with top companies across the industry to deliver a comprehensive Hosted Virtual desktop solution and can help its customers leverage the right provider to help customize a solution for their organization.

Leveraging its experience in deploying Hosted Virtual desktop solutions with customers of all sizes, Rackspace developed the following reference architectures to help educate its customers on best practices. the larger of these two architectures is built for modular scalability, and has been deployed for one Rackspace customer today in a Hosted Virtual desktop environment with over 50,000 users.


Hosted Virtual desktop solutions offer worlds of new flexibility and agility to enterprises large and small. Rackspace has built relationships with best-in-class providers to create virtual desktop solutions for some of the world’s largest companies. Because of their level of sophistication, Virtual desktop environments require advanced expertise in deployment and management. Rackspace can help organizations achieve this while expediting production readiness.


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