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Persistent vs. Non-Persistent Virtual Desktops

by on September 13, 2013

One of the key design considerations when architecting a VDI solution is the use of persistent desktops vs. non-persistent desktops. My colleague, Chaim Landau, wrote a previous blog (http://blog.gothamtg.com/2013/07/18/to-pvd-or-not-to-pvd-2/) around persistent/non-persistent desktops focused on the use of Citrix personal vDisks (PVD). The focus of this blog is more around storage and best practices.

Persistent Desktop

Pros:

  • More or less the same as the physical desktop, but obviously virtual
  • Ability to provide application installation to the virtual desktop itself without a personal vDisk
  • Ability to provide administrative access to the virtual desktop
  • Enablement of cached mode in Outlook

Cons:

  • Need to maintain OS patching solution and application management; much of the same concerns with physical desktops
  • Increase in storage (more on that later)
  • Possible backup of the virtual desktop
  • Provisioning much along the lines of physical desktops

Non-Persistent Desktop

Pros:

  • Updates occur on the master virtual machine or PVS vDisk
  • Overall easier management
  • Less storage requirements
  • Backup just the master virtual machine or PVS vDisk
  • Can utilize personal vDisks (PVD) for application installation (Citrix only)

Cons:

The three common differences are storage, outlook cached mode, and overall management.

Storage

Storage has been a debate regarding VDI since day 1. Citrix and VMware have provided features (vComposer, PVS, MCS) in order to reduce the overall storage footprint. There are also debates on using shared storage vs. local storage. I have seen customers utilize persistent desktops with local storage. Losing the server hosting the VMs is acceptable; however they need the ability to quickly restore those local persistent desktops to another server. When using non-persistent desktops it isn’t much of a factor if a server is lost; very rarely have I seen virtual desktops vMotioned or XenMotioned between servers. However, one of the key benefits of non-persistent desktops is the ability to utilize a master VM or PVS vDisk approach to save on the overall shared storage footprint.

Outlook Cached Mode

This one is always tricky; it has always been a best practice to disable outlook cached mode on a non-persistent desktop. Simply put, why would we want to store the .OST on a virtual desktop that is not static for that user? If a user had a 500 MB mailbox, that .OST would need to be created each time that user logged onto the virtual desktop. However, simply disabling Outlook cached mode will more than likely tick off your Exchange administrators. Here is a good explanation of Outlook cached mode (http://blog.ntiasp.com/2010/11/reasons-for-against-cached-exchange-mode/). This feature in certain cases will dictate the virtual desktop approach.

Overall Management

For customers that are already managing their physical desktops with a management solution (i.e. Microsoft SCCM, etc.) utilizing persistent virtual desktops isn’t all that much different. However the user perception is that if it is in the datacenter, “my” desktop is being backed up, which isn’t always the case. With provisioning tools that I mentioned before (vComposer, PVS, MCS), backing up the master VM or vDisk is a very straightforward process, as is updating the image with the latest patches, etc.

In summary, the type of desktop is only one of many critical design considerations for VDI. Gotham has a defined methodology that can assist in all aspects of desktop transformation. Please contact your Gotham account manager for more details.

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