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One of the early alleged benefits of VDI that vendors pushed in the mid-2000s was that virtual desktops are easier to manage than physical ones.
Vendors claimed that with VDI, numerous users could share a single master disk image, so a software patch or an application update would have to be installed only once into the master image, and voila! -- all the users would be instantly updated.
Contrast that with the traditional desktop environment, where some poor schmuck has to manually update each desktop, one by one, for every change. Even remote software distribution platforms like Altiris or Microsoft's System Center Configuration Manager involve a lot of complexity around building packages, scheduling the software pushes, cleaning up the remnants and so on.
When we have that single shared disk image, we say that those are "nonpersistent" disk images because the disk images do not persist between reboots. No matter what the users do while they're logged on, their changes are discarded when they log off, and they get a brand-new copy of the original desktop the next time they log on. In this case, only the administrator can update that master shared image.
These nonpersistent desktops are the opposite of "persistent" desktops, where everything the users change is still there the next time they log on. Persistent desktops are the more traditional style of desktops. They're what most laptops and desktop computers in the world are today.
So you can see why many people were excited over the notion of just having to install software once for hundreds of users if they were to move to nonpersistent VDI.
What's could be bad about nonpersistent VDI?
There's a major problem with this notion, though. Nonpersistent VDI desktops are theoretically easier to manage, but the reality is that the past 20 years of desktop and laptop management are based on persistent images. So how do you magically go from an environment where each user has his or her own custom environment to a scenario where all your users share a single master image?
The answer is you don't.
VDI vendors such as Citrix and Microsoft tried to minimize this complexity, claiming that you could use application virtualization products like Microsoft App-V, VMware ThinApp or Symantec Workspace Virtualization to "virtualize" apps so that they could be delivered on demand into each user's Windows environment after he or she logs in. In this scenario, a user logs in and gets access to the generic, shared, "nonpersistent" desktop, and then the app virtualization tool kicks in to deliver nicely packaged applications.
Again, this sounds great at first, but the unfortunate reality is that even the bestapplication virtualization tools only have about a 70% to 80% compatibility rate with existing Windows applications. So what are companies to do with their other 20% to 30% of applications? The VDI vendors would tell them to just install them into the "base" shared image, but now that puts organizations right back where they started -- where they have to maintain different base images for different users, manage the updates to those apps and also manage the newly introduced complexity of application virtualization.
These are the reasons why nonpersistent VDI never took off like people first thought it would six or eight years ago, and why VDI experts pushed people towards fully persistent VDI.
If you look at the technology on the market today, we now have new approaches to nonpersistent VDI, which offer 100% application compatibility, including products from CloudVolumes, FSLogix and Unidesk. Next month, we'll dig into how you can use these. In the meantime, start thinking about what it would be like if you could actually get the promised benefits of nonpersistent VDI!
- E-Brief: Architecting Storage for a Virtual Desktop Infrastructure –SearchStorage.com