Want your VDI project to be a success? Choose persistent desktops.
In the world of virtual desktop infrastructure, there are two basic kinds of desktops: persistent (also called personal or one-to-one) and nonpersistent (also called shared or many-to-one). Many VDI proponents claim that nonpersistent desktops are the way to go because they're easier to manage than persistent VDI. With nonpersistent, a single disk image is shared among many users. As each user logs in, he or she gets a clone of the shared master desktop, and then that clone is customized on demand with app virtualization (Microsoft App-V, VMware ThinApp, etc.) or with user environment virtualization (AppSense, RES, etc.).
While this seems like a great concept, the unfortunate reality is that it's impossible to virtualize every single app and user setting with these tools. For example, how do you handle new apps the user wants to install? They can't install to the master image since that's the image that's used for everyone, and they can't install into their own clone because the app would be lost when the admin refreshes the master image. (The ability to refresh a single master image is why you're using the nonpersistent desktop in the first place, right?)
Persistence comes naturally
In your existing pre-VDI environment, most desktops are persistent. Your users have laptops and desktops with hard drive images that persist between reboots. In most cases, users even have admin rights -- they can install their own software, and each image is different depending on the needs of the particular user. Sure, you might use some app and user virtualization (and you should), but any apps that can't be virtualized can be happily installed into a user's image manually.
More on persistent VDI
How persistent vs. nonpersistent desktops affect storage
Persistence affects VDI and Terminal Services security
One of the main reasons that VDI projects fail is because most pre-VDI environments are based on persistent images and most VDI environments are built around nonpersistent images. Companies spend too much engineering time trying to cram diverse images into a common one, and by the time they give up they've wasted several months and pissed off a bunch of VDI pilot users.
So when you move to VDI, don't try to re-engineer your desktops. If you've been using persistent desktops where users have their own admin rights, then keep doing it for VDI. (After all, if you want to move to a locked-down nonpersistent desktop image, you can do that with existing hardware.)
The reason you're not hearing this message much is because the storage technology needed to support VDI users and their personal images has just started coming out in the past year. (That's why many vendors always talked about nonpersistent -- that used to be all they supported.) But now that persistent images on VDI are possible, you can finally design a persistent VDI environment so that it mimics your physical environment. That's a sure-fire way to please your users and to create a successful project.
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