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With nonpersistent desktops, users start each session with a clean desktop each time they log in. If they modify settings or install software during a session, they lose the changes when they log off.
Traditionally, nonpersistent deployments work best in shared computer scenarios, such as store kiosks or school labs, in which multiple users access the same computer. Although nonpersistent VDI offers benefits in terms of performance and maintenance, it is not ideal in situations where users must retain personal data on their desktops. Application layering makes it possible to save user data and user-installed software even in nonpersistent deployments.
How does app layering work?
In a typical app layering product, IT installs applications on virtual disks -- the layers -- separate from the OS but incorporates them in such a way that the apps behave as if they are installed on the same drive as the OS. App layering can help streamline management and better utilize resources in a VDI deployment.
Some app layering products make it possible to configure additional layers for user data and user-installed applications. Unlike the application layers, which are usually based on read-only virtual disks, the personalization layers are based on writable virtual disks, each of which is dedicated to a specific user. The app layering product permanently maintains the writable disks and makes them available to their respective users when they log into their desktops.
For example, VMware App Volumes lets IT assign a writable virtual machine disk file to each user. The file works in conjunction with AppStack to provide a personalization layer along with the application layers. As a result, the writable files can contain customized data, such as local profile information, application settings and user-installed applications.
Citrix's app layering product is based on the technology the company acquired from Unidesk. In addition to advanced app layering capabilities, Citrix App Layering includes a personalization feature called User Layer, a virtual disk that can preserve user profile data and user-installed apps and plug-ins.
Pros and cons of app layering
Both the VMware and Citrix app layering products are ideal for nonpersistent desktop deployments. IT can store user data and make it available when users log into their desktops, providing them with a persistent desktop experience without the associated overhead. IT can even back up and restore the personalization disks should the original ones become corrupted or need to be rolled back.
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Keep in mind, however, that app layering technologies are designed for specific OSes -- versions and editions -- which means users can only run an approved OS on their virtual desktops. Even so, the customization features users get with app layering are a step up from previous approaches to personalization, such as Windows roaming profiles.
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