VDI: To Persist or Not To Persist

Posted by Spencer Sun on Dec 3, 2015

One of the big decisions to make when implementing VDI is whether to provide Persistent or Non-Persistent desktops. Users are accustomed to saving their settings, installing applications and having a consistent, persistent experience on their physical machines. So they'll expect the same in VDI. What should you do if you're in IT?

Back in the day when VDI was first implemented, we simply created a full virtual machine for users and allowed them to connect to it from a physical device. This emulated the persistent experience that they were used to.

However, it quickly became apparent that this was not a cost-effective solution. Giving each virtual desktop the same amount of storage usually provided to physical desktops is too expensive. The VDI vendors came up with a way to reduce the amount of storage required using shared image technologies. VMware provided Linked Clones while Citrix came up with Provisioning Services, and then Machine Creation Services.

Image-based VDI was a good solution for reducing the amount of storage required for each virtual desktop. But one of the side effects was that we got a non-persistent desktop. The nature of using a shared image is that the writable space that Windows requires for things such as event logs, temp files, and user profiles was placed into a cache that was erased when the user logged off.

Non-persistent desktops work in many instances such as kiosk machines, floating pools, etc. But, users still like to be able to save some application settings such as email signatures, even if they’re not saving things like wallpaper, etc.

To this end, a profile management solution was required. Microsoft had given us one - several years ago - called Roaming Profile. Many of us had found these to be slow, messy and unreliable, often getting corrupted when trying to save them to a file share.

The VDI vendors saw this gap and provided a tool to fill it. VMware gave us Persona Management and then User Environment Manager (UEM), both gained through product acquisitions. Citrix gave us User Profile Manager, an in-house developed tool. And then there are the myriad of third-party tools in the Profile Management space - AppSense Environment Manager, RES Workspace Manager, Liquidware Labs Profile Unity, etc.

These tools all work to provide a persistent type experience, at least as far as the user profile goes. They do nothing as far as User Installed Applications goes.

Citrix has provided us with the Personal vDisk or PvD, a solution from the RingCube acquisition. This provides maintainable, writable space for Windows by attaching a new virtual disk to the virtual machine. This disk is usually mounted as the P: drive and contains another virtual disk inside of it, a .VHD file. This allows the segregation of the System writes and the User writes within the PvD.

Unidesk Layers

Unidesk provides the ability to offer user persistence and application deliery using the same technology and workflow. Unidesk's persistent layer provides Windows with a writable space that is NOT a cache, but an actual virtual disk. This layer contains all of the unique information for that desktop or session (Computer ID, Domain SID, event logs, etc.). It is also where anything that the user writes to the desktop will exist, including their profile and, if they have permissions, installed applications. All of this information will exist on the C: drive and the normal registry locations. So, Windows and the application behave as normal.

Unidesk desktop

Also, unlike PvD, this Persistent layer can be backed up and restored to undo user-generated DLL conflicts, malware, etc. Soon, the Persistent layer will even work with Citrix XenApp to make shared sessions as personal as VDI.

If you want to see a preview of persistent layers working with XenApp, comment on this post below. 

Topics: VDI, Citrix XenApp, Non-persistent, Persistent, User Personalization

Posted by Spencer Sun on Dec 3, 2015

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