VDI has come along way over the last several years to solving many of the inherent problems in scale. One important thing to keep in mind is that as with any new feature designed to overcome a limitation in the product, it often comes with its own set of considerations. Specifically, I want to talk about how VMware View Composer and Citrix Provisioning server simplify image management but also impact the potential level of automation you can use when deploying virtual desktops. For anyone who has been developing desktop images, this is not necessarily a new problem but rather one that still exists and needs to be reviewed when deploying Composer or Provisioning Server. For simplicity I am going to use the term Advanced Image Management to describe the linked clone (Composer) and multi-locking of a single image file that Provisioning Server does. The consideration is the same for both, however they are obviously very different approaches to managing virtual desktop images.
When deploying virtual desktops from either the virtual desktop template using Composer or the vDisk image using Provisioning Server the SID is not changed. This tends to be a problem when software references the SID to ensure a unique software agent identity on the desktop or within the Active Directory. I have seen McAfee and Zenworks both have trouble, although I am sure there are many agent based software solutions that would have similar problems. In some cases the software vendor already provides a solution; for example with McAfee it is possible to stop services remove some registry keys and when the system reboots a unique identification is created. Typically you can find this information if the software vendor provides a recommended cloning configuration for its agent or software. In other cases you will implement post setup scripts to ensure any software that breaks in the advanced image management process is added back before the user login. In most cases your VDI environment will have a combination of advanced image management spawned virtual desktops and traditional or virtual desktops that use a full or flat virtual machine hard drive. It is important in the planning stages not to overestimate the cost savings with respect to storage and the use of advanced image management tools. A more pragmatic approach is to divide the total number of virtual desktops into traditional (more costly) and advanced image management desktops. Use the percentage of each to determine the real cost savings of deploying this technology with your VDI environment.