Rethinking desktop virtualisation
It’s not just thick versus thin
Desktop Virtualisation It used to be simple. Users could either run a local operating system, or use a thin client with screen, keyboard and mouse talking to an operating system running on the server. Today there are many models of desktop virtualisation, and few safe assumptions.
It used to be the case that virtual desktops could not handle graphically-intensive applications, for example; but Microsoft’s RemoteFX, which is a feature of Windows Server 2008 R2 SP1, allows GPU virtualisation, in which multiple virtual desktops share a GPU on a Hyper-V server. If you put together faster networks and innovations in virtualisation like this one, the performance gap between virtual and local desktop clients narrows significantly.
Further, it is no longer true that a virtual desktop necessarily runs remotely. VMWare View, for example, is a complete system for composing, deploying and managing desktop images, which are accessed remotely by users running a local View Client.
View Client includes a neat option called Local Mode, in which users can download a virtual desktop onto their client device and take it offline. The user can catch a flight across the Atlantic, continue to work while offline, and sync up their changes to the server once reconnected.
Five ways to skin a cat
So how many kinds of desktop virtualisation are there? Intel distinguishes five models:
- Terminal Services: the old remote desktop model, based on sessions running on the server and accessed by remote desktop.
- Virtual Hosted Desktop: each user has a VM running on the server, accessed by remote desktop. This is inherently less efficient than a session to a shared desktop, but better for isolation and security.
- OS Streaming. In this model, a diskless client downloads an OS image from the server on boot. Streaming means that only the necessary software is transmitted on demand.
- Client side virtual container. This is the VMWare View Client Local Mode by another name. The local client hosts a VM downloaded from the server.
- Application virtualisation. In this model, users have a standard desktop with few applications fully installed. Most applications are packaged and installed on demand.
The term 'virtualisation', already overburdened when applied to desktops, has a different meaning when applied to applications. It describes how applications can be packaged into a self-contained bundle that runs without dependencies and without impacting local resources like the Windows registry.
The trade-off is greater reliability and ease of deployment, versus lower efficiency with respect to disk space and shared resources. Examples are VMWare ThinApp, Microsoft’s App-V – which is part of the Desktop Optimization Pack – and Citrix XenApp, which can work in conjunction with App-V.
While you can argue whether merely using application virtualization qualifies as true desktop virtualisation, there is undoubtedly synergy between the two. If you simplify application deployment, this also simplifies the building of desktop images, however they are deployed.
Citrix FlexCast with XenDesktop supports all five of Intel’s desktop virtualisation models, though it uses different names. The Hosted Shared model uses remote sessions for maximum efficiency. Local VM is the XenDesktop approach to a client side virtual container.
Streamed VHD covers the OS streaming model. Hosted VDI is a virtual hosted desktop, a complete VM running on the server. The idea behind FlexCast is that organizations can support all these different approaches, along with application virtualisation, through a single solution.
One of the attractions of desktop virtualisation is that users are insulated from the limitations of specific devices. Apple’s fashionable iPad is an example. It is a locked-down device that runs iOS; yet fire up an app like Citrix Receiver or VMWare’s View Client for iPad, and it becomes a Windows desktop; not so sexy, perhaps, but ideal for getting on with your work.
The bottom line is that desktop virtualisation has evolved into a flexible and capable approach with few limitations, and obvious advantages for management, security and maintenance. The virtual revolution is not just for servers. ®
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