Thin Images

The key to reducing image count, size, and cost is compromise. The more you put in an image, the less common and bigger it becomes. Big images are less attractive to deploy over a network, more difficult to update regularly, more difficult to test, and more expensive to store. By compromising on what you include in images, you reduce the number you maintain and you reduce their size. Ideally, you build and maintain a single, worldwide image that you customize post-deployment. A key compromise is when you choose to build thin images.

Thin images contain few if any core applications. You install applications separately from the disk image, as shown in Figure below. Installing the applications separately from the image usually takes more time at the desktop and possibly more total bytes transferred over the network, but spread out over a longer period of time than a single large image transfer. You can mitigate the network transfer by using trickle-down technology that many software distribution infrastructures provide, such as Background Intelligent Transfer Service (BITS).

Thin images have many advantages. First, they cost less to build, maintain, and test. Second, network and storage costs associated with the disk image are lower because the image file is physically smaller. The primary disadvantage of thin images is that postinstallation configuration can be more complex to develop initially, but this is offset by the reduction in costs to build successive images. Deploying applications outside the disk image often requires scripting and usually requires a software distribution infrastructure. Another disadvantage of thin images is that core applications aren't available on first start, which might be necessary in high-security scenarios.

If you choose to build thin images that do not include applications, you should have a systems-management infrastructure, such as Microsoft System Center Configuration Manager 2007, in place to deploy applications. To use a thin image strategy, you will use this infrastructure to deploy applications after installing the thin image. You can also use this infrastructure for other postinstallation configuration tasks, such as customizing operating system settings.