For years, the biggest battle in the VDI world has not been Citrix versus VMware or which remoting protocol is better. Rather, it's been between persistent and nonpersistent VDI disk images.
With persistent disk images (also called "1-to-1"), there's a separate and unique disk image for each user. This means that if a user installs something or makes any other adjustments, those changes will still be there the next time the user logs in.
Nonpersistent (or shared) disk images mean that multiple users -- dozens or even hundreds of them -- all share the same master disk image. In this case, every time a user logs on, he or she gets a fresh copy of the disk.
Making the case for nonpersistent VDI
VDI purists argue that nonpersistent disk images are better for VDI because user management is automatic. In other words, you don't have to worry about supporting individual users who break; you can just tell them to log off and log back in, and everything will revert back to the fresh state.
Nonpersistent images also make deploying new apps and installing software updates simple. Installing an app once in the master image means that it's instantly available to all the users because they all share that same base image.
Those on the other side of the fence -- this author included -- argue that nonpersistent images have too many problems and persistent images are better. The main problem with nonpersistent images, we said, is that because all users share the same base image, you have to virtualize all of your apps. This is what allows different users to see different apps.
Unfortunately, traditional app virtualization tools such as Microsoft App-V and VMware ThinApp are only compatible with 70% to 80% of Windows applications. So what do you do with the rest of your apps? Do you maintain separate VDI and non-VDI desktops? Do you maintain separate images?
The other problem with nonpersistent disk images is that they don't support user installed apps. In other words, if a user downloads and installs an application on his or her own, the next time the user logs in, that app will be gone because the nonpersistent VDI image was refreshed back to its master state.
Those two failures of nonpersistent VDI were big enough that I didn't generally recommend it. In fact, I wrote an entire book about it in 2012 called The VDI Delusion.
Bearing that all in mind, as I write this in late 2014, I now believe that technology has advanced enough that nonpersistent VDI disk images are finally an option. Why the change of heart? Two reasons:
First, today we have modern app virtualization products that can virtualize nearly 100% of Windows applications, including products from FSLogix, CloudVolumes (recently acquired by VMware), Liquidware Labs and Unidesk.
Second, the rise of smartphones, tablets and Web apps mean that individual enterprise users don't care as much about installing their own Windows apps anymore. Five years ago, if you gave me a corporate desktop and told me that I couldn't install my own apps on it, I would have quit on the spot. Now? Meh, I have my iPad and a Web browser, so I'll be fine.
The fact that nonpersistent disk images are now a viable option for today's VDI deployments is a big deal. To be clear, I'm not suggesting that nonpersistent is better than persistent or that nonpersistent is the only way. Certainly there are pros and cons to each, and you still have to figure out which one makes sense for your specific scenario.
The takeaway is that in 2014, you have the option of choosing persistent or nonpersistent disk images (or a combination of both) for your VDI projects, and the technology is mature enough to support either decision.
How persistent and nonpersistent VDI affect storage