The virtualization phenomena began simply with server virtualization, but each year seems to bring to light a new use case for virtualization. What we are going to talk about in this article is specifically desktop virtualization.
The desktop virtualization market has experienced substantial growth in the past 2 years. The niche players that own the lion's share of the market are Citrix and VMware. Citrix offers their XenDesktop approach to desktop virtualization and VMware offers VMware View as their solution. If you've been paying attention at all for the past 2 years you've seen the steady growth in the desktop virtualization war between these two virtualization giants. Either way you decide to go, you'll eventually come to the crossroads of deciding whether your virtual desktop infrastructure (VDI) will employ persistent desktops, non-persistent desktops or a hybrid persistent/non-persistent environment.
How do you decide which route to take? First off, you have to understand what these two types of virtual desktops are and their differences. By the time you get to the end of this article, my hope is that you will be able to answer that question for yourself and plan your VDI deployment successfully.
Persistent Virtual Desktops
Let's begin with persistent desktops. A persistent virtual desktop is one in which a user will be able to keep all the configurations and personalization they have created from session to session. Persistent desktops keep the user's profile and documents on a separate user disk, in order to keep the feel of a physical PC. For instance, if you are a user who has a persistent desktop and you create a desktop shortcut to your favorite document, when you end your session and log out of your virtual desktop, it sticks. The next time you come into work, or when you access your virtual desktop from your iPad at home (another post for another time), that desktop shortcut will be there.
Persistent Desktop Pros and Cons:
What's the benefit of a persistent desktop? What you do from session to session sticks with you. What's the downside to persistent desktops? Persistent desktops could potentially become an administrative nightmare. The amount of disk space needed to maintain this setting will grow and datacenter storage doesn't come cheap. Patching and upgrades are now necessary for each persistent image and this can eat up tons of man hours, which usually occur after hours.
Non-Persistent Virtual Desktops
In contrast, a non-persistent virtual desktop does just the opposite. A virtual machine is assigned from a pool of resources when a user logs in. That virtual machine will grab a user's roaming profile in order to establish their personalized settings. When you log into a virtual desktop (note that I said "a virtual desktop" and not "your virtual desktop") and do your work for the day, when you log off, that desktop is wiped clean. Wiped clean meaning, if you created a desktop shortcut, forget about it being there tomorrow when you log on, it doesn't keep changes from session to session. At the end of your session, that virtual desktop reverts back to it's original state before you logged in. Now, don't fret, hopefully your administrators have set up a home drive for you to save all of your work to, that will follow you regardless of what desktop you log into. Usually this is your H: drive or home drive in most organizations. It's never good to save to your C: or local drive regardless of whether you are on a physical PC, persistent virtual desktop or non-persistent. Usually C: isn't backed up and if you lose your session/hard drive, forget about what was saved locally, it's never coming back.
Non-Persistent Desktop Pros and Cons:
What's the benefit of non-persistent desktops? Patches and upgrades are more easily applied to a single image in a resource pool of virtual desktops which cuts the man hours required for management. The downside would be having to sync roaming profile changes between multiple sessions. The time it takes to log on will gradually increase with the amount of changes that are applied and updated to each profile.
Now that we understand the definitions and differences between these two virtual desktop types, let's figure out why you would chose one over the other, or have a heterogeneous mix within your VDI.
How Well Do You Know Your End Users?
Let's start with getting to know your end-users. How many users will be requiring a virtual desktop? Are you planning on deploying a virtual desktop to every employee in your organization? Are there any power users? What kind of endpoints are your users accessing their virtual desktop on? Wow, that's a lot of questions right off the bat, but questions that you need to know the answers to before you decide which type of virtual desktop you are going to deploy.
In most situations I've encountered, you will start off with a pilot program involving about 50% persistent and 50% non-persistent desktop deployment. The persistent desktops you will want to deploy to your power users, C level executives and such. The non-persistent desktops will go to the users who require less customization and are your typical 9 to 5 users. You want your C level execs to not deal with roaming profile issues while accessing their desktops from various endpoints and locations. A C level exec doesn't want to feel like they are on a virtual machine at all, they want to feel like they are at their desktop and all of their shortcuts, backgrounds, OS and applications are untouched.
If you are in a lab setting at an educational institute or a library, you want to be 100% non-persistent. You don't want users leaving any customization behind when they log off at the end of their lab time. I can't think of a more perfect scenario in which you would utilize 100% non-persistent desktops. If you are the systems administrator at a high powered law office, you want to be 100% persistent desktops. Why? Simply because you want each of the attorneys and or partners to have all of their applications and personalization in tact in order to have the least amount of intereference in their work environment. The same would apply to the paralegals and administrative assistants in a law firm, these are people that will be making profile changes on an almost hourly basis most likely. Of course there are scenarios in which you would deploy a heterogeneous mix of persistent and non-persistent desktops. You will find that a heterogeneous mix is the most commonly deployed VDI configuration and works well in most situations.
There are pros and cons to both types of virtual desktops. There are definitely scenarios in which you would deploy 100% persistent or non-persistent desktops. The end user and the way they interact with their virtual desktop should drive your decision as an administrator. Look at your environment from all angles and apply the principles we've discussed in this post to aid in your decision for your VDI deployment.
As always, you will get push back from some users in your organization when you deploy VDI regardless of the type. I think you will find that most end users will blame any degradation in speed or application performance on virtualization, this is not uncommon. Good user education and applying best practices put forth by the vendors will help keep your VDI deployment and management simple and easy to manage.