The dark side of single image management

Single image management is supposed to reduce storage requirements and make management easier, but it has built-in performance and capacity issues.

Theoretically, the benefits of deploying a single image to all your VDI users include convenience, ease of management and fewer storage requirements. In practice, however, there are some caveats around single image management you should be aware of.

One of the reasons some shops deploy virtual desktop infrastructure (VDI) is to take advantage of single image management. Single image management software uses driver injection technology to stream an image to a PC. It also keeps track of configuration files and has a driver library, so it knows which drivers each PC needs and has them available. There's one image -- a golden image -- that you can deploy to many desktops and users. Then you only have to patch and update one image. It might sound easy, but it's actually not so simple. And what's more, you don't need VDI to take advantage of single image management.

What are the downsides of single image management?

When you deploy a VDI image to a group of users, the image may be locked, but users can still customize their desktops and install new applications. All that customized information is stored separately from the image, either locally on the hard drive, on the shared network drive, or on a virtual drive. But as customizations increase, more personalizations need to load each time a user logs into a virtual desktop. This can create performance issues and negate one of the benefits of using a single image for all your users: It won't save in storage requirements if every user needs tons of space for his expanding personal customizations. Instead of easier management, you'll have performance and capacity problems to deal with.

What can admins do?

When that storage reaches critical mass or application and OS patches are released, you can rebuild and redeploy the base image. Keep in mind, however, that then the new base image could be incompatible with user customizations, forcing workers to reinstall or reconfigure their personal settings and third-party applications.

More on single image management

Why VDI should persist

Let's get this straight: Nonpersistent vs. persistent desktops

There are some image management tools that can help, but you'll no longer be using a true single image. For example, with Windows Server 2012 image management, you can see your whole VDI environment at a glance, deploy patches as they become available and identify pools of users with the same requirements. Instead of having a single image for all your users, you'll deploy different images for smaller groups of users with common needs. Alternatively, VMware's Horizon Mirage lets you split images into layers. You'll have at least one base OS image, plus various driver libraries and application-layer images, then you can deploy different combinations of drivers and applications to the users who need them. This lets you update one layer of the desktop without disrupting the others.

How do I use single image management without VDI?

Disk streaming tools let you do the same thing as using single image management in a VDI environment. With single image management and VDI, you're using one image for every virtual machine, so each user loads the same image and the only things that save are the differences after the boot. With disk streaming, you can stream the same image to any networked computer instead of being limited to virtual machines. Disk streaming tools only send the basic data that the system needs to boot Windows across the network. Once Windows is loaded, the disk streaming tool only sends information as it's needed. The data on the device can be persistent, nonpersistent or wiped clean from one boot to the next, so users get a new copy of the same desktop each time they log in -- without VDI.

This was first published in April 2014

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