Value of VDI Assessments

Disclaimer: This is a copy of the post that I made for TechTarget recently.

The past eighteen months has seen huge investment by VMware within the EUC space, with the arrival of Sanjay Poonen and Horizon (with View) 6 which introduced application publishing in the Advanced edition.  Finally we had an emerging contender to the heavy weight Citrix XenApp.

With this investment from VMware, the past twelve months have seen an increased number of customers looking at virtualising desktops and applications.  The first part of the engagement process is to access whether or not a physical computer is a virtualisation candidate.  To do this we undertake a desktop assessment.

What Is a Desktop Assessment?

First of all, I want to define what is meant by desktop assessment?  From this blog post perspective it is a piece of centralised software that collates information from remote agent’s installed on end user devices which are perceived to be candidates for VDI.

There are plenty of tools on the market from providers such as:

So the question is what value do these assessments bring to a business that is contemplating a move towards VDI?

Different VDI Guest Operating System

The first question is are we staying with the same operating system or moving to a new one?

If you perform a VDI assessment on a desktop operating system which is going to be replaced with a newer version, what value are you really obtaining? Not a lot, the applications will most likely require updating to support the new OS and this in turn leads to different requirements for compute and storage requirements.

Same Operating System

If you are going to have the same operating system you will get more value from the desktop assessment.  However it’s worth bearing in mind that the results from the desktop assessment often over inflate your compute metrics for example:

  • Compute resources used by in guest Anti-Virus are likely to be offloaded to a host based alternative
  • Compute and storage resources for Windows updates will often be negated by VDI tools such as PVS, MSC and Linked Clones
  • Applications installed by the end user will most likely be removed from the ‘master image’
  • VDI ‘master image’ will be optimised with services, widgets and applications being disabled or uninstalled

This can be viewed as a good thing as you can often show a slightly higher consolidation ratio per physical host.

What about Peripherals?

This is where desktop assessments come into their own.  Most IT departments I have spoken to always say ‘yeah we know what applications and devices our users use’, yeah right!

Desktop assessments will inform you what Parallel, Serial and USB devices are connected to the user’s computer.  This gives you the visibility to determine whether a particular user’s device is appropriate for VDI.

What about Licensing?

Desktop assessments are good for capturing what applications are used by users and what devices have what software installed.  However they often fall down in a number of areas:

  • Application dependencies, to determine why you have five different versions of Java installed
  • Often look to see if an executable is launched not whether an application is used to read or edit a document which can have a huge effect on license cost
  • Application readiness and/or virtualisation assessment, will the application work on Operating System ‘x’ and is it capable of being virtualised?

Often this area is overlooked and requires a large effort from a separate workstream outside of the desktop assessment.  Use the information from any desktop assessment as a starting point.

Group Policy

Most desktop assessments rely on an in-guest agent on the end device to capture metrics and pass them back to a central collection repository.  So what happens when you are waiting for that agent to start? The answer is simple nothing, you miss collecting data on anything that happens prior to the agent starting.

When the agent does start, the metrics collected for login time or log off time can be skewed by group policy applied to the computer object.

Ask yourself the question how often is a new OU created for VDI deployments?

What about the storage?

We have already established that the in-guest agent doesn’t start until when the operating system is ready so we have missed boot metrics IOPS.

Desktop assessments have the ability to capture steady state information which is OK as long as there are no other bottlenecks skewing the provided information.  For example:

  • Is paging occurring which is causing disk I/O to increase?
  • Is the limiting factor the hard drive itself and if unleashed from a 7.2K SATA hard drive, what IOPS would be consumed?
  • Are Anti-Virus scans causing peaks in provided disk I/O information?

What is the value?

For me, the value in a desktop assessment for VDI is in the following items:

  • Enables you to take a ‘bird’s eye’ view of what users are virtualisation candidates when items such as peripherals are taken into consideration
  • Provide user classification into different classes for resource consumption e.g. low, medium and high
  • Enables you to determine concurrent login and logoffs which can help determine storage sizing requirements
  • Gives you an insight into what applications are used by users

Final Thoughts

The desktop assessment does have some value in the VDI world, it is not a panacea to provide you everything you need to know on your journey to VDI.

Do I use desktop assessments, yes is the answer.  However it should be mentioned with a limited use case.  Most of the value comes from a pilot and load testing with products such as LoginVSI to determine the density of users per host.

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