Choosing the right virtualisation technology

Irwin: Virtualisation helps simplify management

Experts predict that 2010 will be the year that many organisations finally switch on to the benefits of desktop virtualisation, but the technology has moved on since VMware first started to dominate the market with its Virtual Desktop Infrastructure (VDI) platform.

“There was a convergence of thinking around this, and VMware initially picked up the desktop and dropped it into the datacentre as a complete image,” says Roy Illsley, senior analyst at research firm Ovum. “But it was later realised that this approach does not offer good management or flexibility, so vendors such as Citrix re-archi­tected it around splitting applications out and building virtual machines on the fly.”

Ian Moulster, product manager for Microsoft’s .NET platform, believes VMware’s approach was too simplistic. “VMware was saying ‘Our solution is Virtual Desktop Infrastructure and that is what you need’, but while that is easy to explain, it is only one way of doing [desktop virtualisation] and does not offer the full range of options,” he says.

“Our experience,” says Citrix European product manager Patrick Irwin, “is that people like running the desktop operating system [OS] in the datacentre, rather than the server OS sending it out in some way to the end point device. While this has a place with certain user groups, it is not a panacea for everyone.”

What is a virtual desktop PC?
VMware’s initial VDI approach was to build virtual images of desktop PCs or virtual machines (VMs) on servers in the datacentre, which were tied to individual users accessing them over the network using VMware client software.

The packaged VM contains both the OS and applications that local machines access, plus portions of the server’s CPU, RAM and hard disk space put aside to handle the local client’s needs – little or no processing is carried out on the local machine.

That local system can either be a “fat” desktop PC, “thin” client machine or a laptop running virtual software, providing basic I/O resources such as mouse and keyboard, while the use of specific add-on software can also enable users to plug in USB peripherals.

Alternative approaches
This type of virtual desktop infrastructure is still popular, but differing approaches to desktop virtualisation are being pushed to the fore. Microsoft and Citrix in particular favour amending and expanding previous remote/terminal services and application virtualisation technology to provide similar virtual desktop experiences, while VMware has amended its own products to offer alternative approaches too.

One of the challenges people have now is weighing up the pros and cons of different vendor platforms.

“One size does not fit all,” says Illsley, “and that makes things more complex. You cannot say ‘here you go, this is VDI and this is how it will work’, because there are four or five varieties of [desktop virtualisation].”

Microsoft has its own version of VDI called Microsoft Desktop Virtualisation, which was created by modifying its existing Terminal Server product and integrating it with the Hyper-V hypervisor in Windows Server 2008. The management part of the equation is delivered by System Centre Virtual Machine Manager 2008, while technology partner Citrix takes care of the desktop end with its XenDesktop product (formerly XenApp). Other companies offering desktop virtualisation components or platforms include Sun Microsystems (now owned by Oracle), Parallels and Systancia.

VMware has also packaged its various virtualisation components, including its ESX Server and View VDI products alongside other management tools into a complete product suite called vSphere.

The main differences between these products centre on how much data is actually transferred from the server to local client systems – whether individual VMs are assigned to specific users or local systems rather than shared among multiple users simultaneously – and to what extent the VM is mapped to local hardware resources, if at all.

One model relies on Microsoft’s Remote Desktop Protocol or alternatives such as Citrix’s Independent Computing Architecture or Virtual Network Computing, to present users with a window onto a virtual desktop image being run on a server – something that allows any local hardware client, from laptops to smartphones, to be used for access purposes.

“You do not want to send the data to the end users, because you do not know what device they are running, so all the benefits of managing, updating and patching centrally are there,” says Irwin, though he acknowledges that in some cases an application running on a shared server infrastructure is not suitable because it needs access to CPUs and graphical processor units, as well as RAM to run efficiently.