Personal vDisks – Part 1!

Well, it’s been a while since I’ve written an article and I’ve got plenty to write about really…  I’ll start with Citrix’s latest edition to the XenDesktop family, 5.6 and Personal vDisks.  Also after writing out all I’ve discovered about Personal vDisks to date, it is too big to put into one single blog so I’ll be splitting it out into bite sized pieces, like the mini Battenberg’s Mr Whathisface does.

Now, due to a customer’s current demand for a lot of Private VDI desktops as part of their big migration solution, we’ve (I’ve ?) decided to go with the new Personal vDisk technology so we can utilise the same single PVS image that we’ll be using for the hundreds of pooled desktop thus achieving a more manageable solution for the customer.  Here lays the first two problems though;  What is Personal vDisk and How does it work?  I shall try and explain.

Personal vDisks allow users to be able to install their own applications without the need for admin rights or compromising the base OS.  Complete separation is achieved by partitioning the user applications away from the OS.  You can even install applications that use drivers!  The Personal vDisk (PvD) also allows for basic profile management and user personalisation to be persisted even when using a Pooled image that is read-only.

Now, lets dig a bit deeper!  Personal vDisks are a VHD file that is attached at HYPERVISOR level (not Streamed) to an individual Virtual Machine (VM) whether it be created through MCS or PVS.  Once the PvD is attached to a VM, redirection of the C:\Users (C:\Documents and Settings for Windows XP) and C:\ProgramFiles folder takes place allowing user installed applications and personalisation to persist even after reboot.

So far, so good, eh?  Well, if we dive deeper into the depths of the PvD, we can see that not only the Users folder is redirected by also the RadeCache and RadeStore, for those using Citrix Streaming. 

PvD Explored

You’ll also notice there is a UserData.vhd and a UserData.vhd.thick_provision.  The UserData.vhd is the thin provisioned VHD that holds user installed applications and the UserData.vhd.thick_provision I believe is either a placeholder for the User installed apps to “mark out” the disk space it has been allocated or is actually the thick provisioned UserData.vhd.  This is a bit confusing at this stage and there appears to be both a thick and thin provisioned Apps area but further testing will show so watch this space for more on that!

As you can see, by default, the PvD will be created with drive letter P:\  When you create the Machine Catalog for the pooled desktops that will have a PvD, you can change this.  The application partition of the PvD by default is given the drive letter V:\ and is hidden.  

Computer window with PvD attached

If your enterprise uses either of these drive letters, it would be advisable to change these from the default.  To find out how to do this, see the following Citrix article –

By default, when you create a PvD, no matter the initial size, it will split the disk equally between User Profile and Applications.  E.g. if you have a 10GB PvD, 5GB will be for User Profile, Data, Docs, Personalisation etc. and 5GB for user installed applications.  I will be exploring this setting and how to change it and what it means in a later blog post coming soon!

This covers the “basics” of the Personal vDisk and in the next blog, I will dig a bit deeper into the practical side of using Personal vDisks within XenDesktop.


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