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Overview Desktop virtualization refers to technologies that separate a monolithic personal computer desktop environment comprising hardware, operating system, applications, data, and personal settings independently of each other.

Currently, there are two primary approaches to desktop virtualization,

server-side and client-side, respectively. Adoption to server-side desktop virtualization, which is also referred to as Virtual Desktop Infrastructure (VDI), has been slow due to its installation complexity and exorbitant system integration costs in addition to other growing concerns over scalability, performance, and anytime (offline) access. On the other hand DeskStream employs client-side desktop virtualization technology to offer an optimized and high performance Dynamic Virtual Desktops (DVDs) by combining the best of centralized IT management and client computing together to deliver truly anywhere, anytime personalized desktop execution on any device resulting in significant cost savings and uncompromised user experience. How DeskStream DVDs could be leveraged to complement VDI deployments to address the inherent limitations such as performance, desktop image management, scalability and offline computing is the topic of discussion in this paper.

What is VDI? Virtual Desktop Infrastructure (VDI) is a platform for delivering Hosted Virtual Desktops (HVDs) from the data center. VDI leverages server virtualization technology to provide many additional benefits and significant improvements to computer hardware efficiency, security, and centralized desktop manageability. Server virtualization is a method of abstracting the underlying hardware resources to run multiple independent (virtual) operating systems referred to as Virtual Machines (VMs) on a single physical computer. This technique achieves server consolidation which slashes hardware asset acquisition and maintenance costs that can result in significant cost savings for an organization.

As a single physical computer is logically turned into anywhere from eight (8) to thirty-two (32) virtual servers, it is possible to run that many VMs on each server thereby achieving high CPU utilization. The user’s desktop environment comprising applications, data, personal settings, and the operating system, also referred to as HVD, runs in a dedicated VM on a server sharing a pool of virtualized server computing resources. The desktop view is presented to the user typically on a thin client device over the LAN/WAN. As the underlying OS and the user’s desktop environment is tightly coupled, each HVD size is tend to be rather large ranging anywhere from 30 to 40 GB.

How It Works As per VMware source, HVDs usually are made available to end-users via “pools” of virtual machines. A pool is a group of virtual machines that are derived from the same base image. Virtual machines can be created within a virtual machine pool. One of the advantages of pools is that they allow rapid provisioning of new HVDs and provides a logical grouping for access control. Additionally, administrators can specify configuration settings based upon pool membership. Typically, there are two types of pools – persistent and non-persistent.

Persistent Pool With a persistent pool, users are assigned to the first available virtual machine in that pool. At each subsequent login time, the user is directed back to that same VM. This ensures that users easily can access their personalized settings and data, as that information is stored with the virtual machine.

Non-persistent Pool With a non-persistent pool users are assigned the first available virtual machine when they log in. Virtual machines are transient, with no guarantee that the user will return to the same virtual machine twice. Subsequently there is no guarantee of persistent storage of user personalized settings either.

There are trade-offs associated with both types of pools. For instance, persistent desktops offer a more personalized computing experience, but may require more management than their non-persistent counterparts. On the other hand, non-persistent VMs can be destroyed and recreated after each use reducing same management.

1st Generation VDI st

In the 1 generation VDI solutions, users’ applications, data, personal settings, and operating system files are all stored in a persistent VM requiring more than 30 GB of storage capacity that increases linearly with every additional user. Granted this approach preserves user settings and applications across multiple sessions, but organizations would have to deal with hundreds of thousands of OS and application images, requiring massive storage capacity which comes with prohibitively high storage cost. On the other hand, only the standard corporate applications and operating system files are stored in a non-persistent VM but after every session user’s personalized settings and installed applications are lost. This approach reduces IT management and minimizes storage but at the expense of loosing user settings after each session. A small percentage of enterprises who already adopted VDI based centralized desktop management have come to realize the installation complexity, exorbitant system integration costs, exponential scalability costs, and increased IT resources for effective management. As a result the total cost of ownership per desktop went up by 10-15% when compared to traditional desktop computing. It turned out, the cost of rolling out a virtual desktop infrastructure, including servers, SAN storage, high availability, network bandwidth, thin clients and software licenses, has far outweighed the potential savings in IT labor and security costs.

2nd Generation VDI The promise of second generation VDI solutions is to enable centralized management without compromising the end-user experience while delivering efficiency, scalability, and management improvements, all while reducing desktop total cost of ownership. The current solutions have moved away from a one-to-one relationship between users and OS images in order to realize substantial SAN storage cost savings and to alleviate IT from the mundane rigors of managing, patching, and updating all those images. That being said, the existing VDI didn’t solve either the image management or offline computing problems in a convincing way. VDI has introduced a concept of read only master image template comprising operating system from which tens of hundreds of thousands of VMs are snapshotted or cloned into different persistent or nonpersistent pools. This, in essence, requires managing only one single copy of Windows operating system irrespective of the number of VMs derived from it. In case of persistent pools, when a new clone for a new VM is created, a small read-write disk image file is created which is specific to that VM. This disk image file is referred to as differential file to which the user’s personalized settings and data are written. At the time of booting a VM, the read only master image and the read-write differential files are linked together forming a process referred to as linked clone. By virtue of maintaining a single read only master image throughout the process, all cloned VMs can simultaneously share the same master image minimizing the storage needs significantly lower. Any user updates are written to the differential file.

That being said, there are two caveats to consider here: 1.

For a linked clone feature, where many users share a single master image, to work the provisioned applications need to be dynamically delivered to each user’s VM on-demand. This requires an application virtualization tool such as App-V, ThinApp, or XenApp. The problem, however, is that these application virtualization tools can’t virtualize 100% of applications. This issue could be resolved in other ways such as installing the apps into the VMs in the conventional way via SMS or by having multiple master images. Either way, the projected cost savings would be affected significantly as a result of utilizing more storage.


Each time a patch is applied to the shared master image or a new corporate application is added, the differential file of cloned VMs doesn’t work and have to be thrown away. When a patch is applied, it affects the physical blocks in the master image and the cloned VMs linked back pointers wouldn’t know how to hook back with the master image rendering them useless. Overall applying a patch or adding a new application to the master image is a complex process, IT would have to go through a series of steps to recreate a differential file for each persistent VM from scratch and restore each user’s personalized settings from a backup file stored separately.

VDI Barriers Gartner publication (G00165252) dated 02/2009 reports the following barriers or challenges as the stumbling blocks to Hosted Virtual Desktop (HVD) deployments: Higher entry cost Especially in case of first generation VDI, the cost of rolling out a virtual desktop infrastructure, including servers, SAN storage, thin clients and software licenses far outweighs the potential savings in IT labor and security costs. Complex management and manageability Managing multiple VMs means managing multiple copies of OS and applications with products like SMS is complex and tedious. On top of this, VDI requires expensive SAN storage and high availability to move VMs from one server to another in case of a server failure driving the operational costs higher. Less-than-ideal application performance Several VMs are executed on a single server. This count could vary from 8 to 32 VMs per server. Depending on the number of VMs executed on each server and the kind of applications executed in each VM, the user experience in terms of application performance and rendered desktop view response could vary significantly. Additional Windows licensing cost In traditional desktop computing, organizations would only require purchasing one OS license per PC. In case of VDI, organizations would have to purchase two licenses per VM, one OS license for VM and other for the end point such as a thin client used for rendering the desktop view.

In addition to above listed barriers, organizations need to be aware of other VDI limitations that could potentially affect the cost savings model:

Limited Applications Support A new feature from VDM3 onwards is the linked clone which is used to enable many users to share a single master disk image. A great cost savings considering organizations didn’t need to allocate 20-30GB on SAN storage for each single user. But for this to work, applications have to be dynamically streamed on-demand into the user’s disk image. Here lies the problem as the existing application virtualization products such as ThinApp or App-V can’t virtualize applications out-of-the-box. To virtualize an application, it has to go through a series of packaging and sequencing which might take weeks to months to perfect thereby destroying the projected cost savings model by these VDI vendors. Inflexible image management Typically VMs are rebuilt at the start of each day from a series of centrally managed components which is time consuming and secondly, VMs aren’t available for anytime access. An alternative is to store the entire VM on disk at the end of each day, and keep it ready for quick access instead of rebuilding each day, but increases storage and management costs. Whenever a patch is applied to the master image, the differential file of VMs, where the user’s personalized settings and applications are stored, have to be thrown away as the linked clones don’t know how to hook back with the master image after a patch is applied. Subsequent snapshotting of cloned images and recreation of differential image file for each VM is a complex process. VDI offers persistent mode at an extra cost. Each VMs differential file data is redirected to a completely separate storage which doesn’t get purged even after the master image is modified. This saved information is used to recreate a VMs differential file after a patch is applied to the master image. Lack of support for offline mobility VDI continues to stumble over what to do when the end user disconnects from the network. In a typical setting, a virtual machine is running on a central server, not on the end user's desktop device. Once the user disconnects, the ability to do work is disconnected also. Lately, there is a provision for the users to collect a streamed down version of the virtual machine to carry with him on disk, but requires a client hypervisor to run the VM on a client device making the entire user experience less-then-ideal. Lack of application personalization VDI’s inability to let users keep their application preferences and history such as passwords, Web site history in your Web browser, or the macros and settings and list of recently opened documents in Microsoft Word Lack of support for personal applications Installing user preferred applications would break down especially in the linked clone scenario. Because these apps write data to the read only C: drive and system registry, they wouldn’t work. Other alternative would be to make a copy of the master image to create a new VM instead of a linked clone in which case the user could install apps as he likes, but increases storage (around 40 GB for each copy of VM) and management costs.

DeskStream’s Dynamic Virtual Desktop (DVD) Platform DeskStream offers a high performance client-hosted desktop virtualization platform which transforms centralized desktop management by employing patent pending technology to deliver truly anywhere, anytime personalized desktop execution on any device resulting in significant cost savings and uncompromised user experience.

DeskStream employs a unique and innovative virtualization approach whereby, it decouples the users’ workspace comprising applications, data, and personal settings from the underlying operating system and device.

How it Works

As a result of applying the virtualization abstraction between the operating system and application layers, not only the users’ workspace was decoupled from the device as in the case of VDI but it also goes one step further from liberating the users’ workspace from the underlying operating system as well. This approach opens up several promising and exciting opportunities to deliver compelling solutions. On a high level, the DVD platform operates on the following principles. 1.

Genuinely User-centric – Delivers true stateful workspace on-demand for native execution on any end point; workspace is delivered in its entirety comprising applications and profile to the end point and executed using the local computing resources to provide the ultimate user experience.

2. OS Independent – Smartly engineered solution decouples the users’ applications and profile from the underlying OS enabling workspaces run across multiple operating systems such as XP, Vista, Windows 7, or Linux. Just like a Web application runs in any browser, a decoupled virtual workspace should run on multiple operating systems, all while using the same virtual workspace. 3.

Device Independent – Virtual workspace applications aren’t installed on the end point thereby allowing choice of devices to choose from including a diskless thin client for executing a virtual workspace.


Mobility & Offline – A virtual workspace devoid of OS is light weight and portable, making it feasible to carry around even on a USB stick to execute where needed when needed on any device, be it online or offline.


Brings web paradigm to desktop applications – Just the same way a single web application is published to tens of thousands of users via a web browser, DVD platform manages a single master copy of each application along with discrete copy of users’ data and personal settings for mass deployment.


Simplified centralized management - Leverages template technology to create tens of thousands of virtual desktops instantaneously from a single template making management and scaling an effortless process.

Virtual desktops are provisioned with applications from a single source with absolutely no

duplicate images.

Deployment Client-hosted virtualization is becoming more relevant especially in today’s market where more and more organizations are facing with shrinking IT budgets. DeskStream’s DVD Platform is a very compelling solution for both IT administrators and the end users alike. It delivers a reliable and scalable centralized platform and enables Enterprises to help create, secure, deliver, and streamline the lifecycle of virtual desktops swiftly and efficiently. Simplicity of operation combined with a unique desktop virtualization approach sets DeskStream apart in providing solutions to wide range of challenges in a simple and costeffective way. A simple data center with a few servers is all it takes to launch this platform. As this platform doesn’t require rather expensive and complex infrastructure resources the time-to-centralized-desktop management is incredibly quick and light on resource utilization which helps reduce data center capital costs and TCO for each desktop. Centralized nature of DVD’s virtualized solution alleviates the pain of rolling out solutions on each individual desktop thereby increasing the manageability. OPEX reductions would be realized due to consolidation of the server footprint, provisioning of applications, and patches centrally. Administrator can choose to make the user desktops as locked down or as open as possible by choosing the appropriate policy settings. The company can thus easily enforce compliance in the workspace. Virtual workspaces are delivered to any of the endpoints connected to network and run locally. The platform employs a variety of deployment options such as LAN, VDI, Internet, including offline usage to deliver a virtual workspace to the end point.

Use Cases Mobility and Offline Computing Trend is the mobile computing focused lifestyle requiring flexible technology with the reach and low cost of distribution for delivering workspaces on-demand over the Cloud in a whole new way. With DeskStream, users could be empowered to execute their personalized workspace environment securely from anywhere, be it at the corporate office, branch office, home or on the road, and on any device when needed.

Mobility and offline computing is supported even while the users are disconnected from the network for continued productivity, all without compromising user experience. Disaster Recovery Business continuity is becoming an increasingly important aspect of enterprise desktop management. As devices, systems, and software have become more complex, organizations are constantly finding ways to deal with potential disasters. With DeskStream, the users’ data is continuously synched with network storage, disaster recovery from a stolen, lost, or damaged laptop is quick and easy. Users could be up and running quickly in case of disaster strikes with quick access to a newly constructed virtual workspace via a network link or by simply plugging in their pre-installed USB drive. Outsourcing Call Centers have fluid business opportunities requiring dynamic scaling to accommodate a spike in demand. Security compliance has been a perennial challenge for IT administrators while delivering corporate desktops to temporary staff, contractors, and outsourced work force. Solving this has never been this simple. DeskStream’s DVD Platform delivers secure desktops on any device and executes them in a virtualized environment without compromising any of the corporate data. Unified Computing Financial institutes have a requirement where users’ should have a unified virtual workspace in which sensitive applications are run in HVDs and most other apps are executed natively on the end point. This entire computing experience must be seamless and transparent to the users. This approach enable organizations to offer flexibility, better user experience in terms of performance and response time, and finally enforce compliance. Thin Computing Some Enterprises are warranted employing thin computing in addition to the traditional desktop computing to meet their business objectives, but at a higher CAPEX and OPEX. With DeskStream, they would not only transform a thin client into a full-fledged PC, but also reduce management complexities and energy consumption dramatically enabling them to make the switch to Green.

DVD as complementary to VDI While VDI is very effective in some use cases such as catering task workers and outsourced temporary workers, it breaks down when it comes to knowledge or mobile workers due to the aforementioned limitations. The crux of VDI problem is the disk image management and offline computing due to its inability to decouple the users’ workspace environment from the operating system. If there was a way to optimize VMs by decoupling the users’ workspace from OS, it would bring tremendous flexibility to the way VMs are stored and managed whereby the overall management tasks are reduced to a bare minimum in addition to bringing other features such as true stateful workspaces and mobility into play. DeskStream offers such a solution platform.

Architecture In this scenario, a typical VDI implementation is limited to managing a read only master OS image, whereas the users’ workspace management is offloaded to DeskStream’s DVD platform. It is no longer required to maintain persistent pools, non-persistent pools, or VMs differential files. DVD platform is integrated on the existing VDI infrastructure resources by adding a Windows Server 2003/2008 which is essentially used as a file server for storing and managing the users’ virtual workspaces. The entire DVD platform software components can also be run in a dedicated VM inside a single physical server. The administration console is used to create, provision, and manage the life-cycle of workspaces.

Benefits Integrating DVD over an existing VDI brings a paradigm shift to the way VDI behaves enabling a whole new set of features and/or benefits which were deemed impossible to achieve all by itself. Reduced TCO Deployment and support costs plummet – Managing a single master copy of OS image on VDI and a single copy of each application along with the data and settings of each user on DVD platform dramatically lowers the SAN storage and management costs. When administrators want to apply a patch or provision new applications, they simply make an update to the master copies and those changes are automatically published to the users at their next login. Out-of-the-box Application Support VDI’s linked clone environment makes it impossible to install either corporate or personal applications without breaking the master image. Whereas it is a trivial process on DVD platform – just as in the case of a traditional desktop, IT or users can install any windows applications via CDROM or Internet and execute them immediately, all without making any application code modifications, packaging or sequencing.

Business Agility VDI require users to stay connected to the network in order to access their virtual desktops. With DVD over VDI, users would get to enjoy the flexibility – they can either access their desktop through VDI or get a virtual workspace delivered on-demand over the network seamlessly for local execution on any device where needed when needed. Indeed, users can copy the entire workspace on a USB stick, carry it in their pockets, and execute it anytime, on any device. All workspace changes made while being offline are synced with the centralized file server once they get connected to the network. Personalized Computing There is no longer a need to create linked clones, persistent pools, or differential files to keep track of the personalized settings and data to deliver a stateful virtual workspace. A VM’s two components, OS and virtual workspace, are synthesized at boot time on-demand and any changes made to the personalized settings are immediately synced with network storage thereby preserving personalized settings even after a VM is terminated.

Complemenatry & Alternative Solution to VDI