Both profile redirection and folder redirection help address issues around storing user data, but one comes with more management and bandwidth concerns than the other.
One of the main challenges that virtual desktop administrators must cope with is storing user data. Most virtual desktop tools let you create personal, fully writable virtual desktops, but it's usually easier to manage static virtual desktops. Either way, users need to be able to create and retrieve data.
The Windows operating system has two different solutions to this problem. One answer is user profile redirection and the other is folder redirection. Although these two mechanisms are somewhat similar, they are not the same. With profile redirection, the changes users make to their desktops are persistent whereas with folder redirection the opposite is true. Both options are bandwidth-hungry, but some fixes in Windows 7 and 8 have made folder redirection more efficient.
Profile redirection versus folder redirection
User profile redirection stores a user's profile in a centralized location. This makes the entire profile accessible regardless of which physical or virtual desktop a user logs into. The nice thing about user profile redirection is that any customizations the user makes to his desktop follow him from one virtual machine to another without affecting any other users' virtual desktops. For example, if a user created a shortcut on his desktop, then that shortcut would be accessible to him regardless of which virtual desktop he logs into.
At first, user profile redirection might sound like an ideal way to store user data in virtual desktop environments -- and it does have its place -- but it tends to be bandwidth intensive. This isn't much of a problem if users have relatively small profiles, but it can become quite disruptive as profile directories grow over time. In some cases, the full contents of a user's profile directory must download to the virtual desktop as part of the login process. If a user has a multi-gigabyte profile, then the login process can take an excessive amount of time to complete.
Similarly, the amount of time required to log out can also be extreme. When a user logs out of the system, Windows copies any changes that the user has made to the profile from the local machine to the redirected profile location. Microsoft did introduce a change in Windows 7 that can help decrease log off times, however. Now you can configure background uploading on a scheduled basis. For example, you can use a Group Policy setting to begin the upload process an hour before users are scheduled to go home. Similarly, an upload schedule can force uploads on a periodic basis throughout the day.
For some shops, folder redirection might be a better option than profile redirection. User profiles contain special library folders that are designed for storing user data such as documents and pictures. With folder redirection, folders associated with user profiles are redirected to a network share. This means that the data a user saves to his folder is written to a centralized network location rather than being stored directly on the virtual desktop or in the user's profile folder.
More on folder redirection and storing user data
Tips and tricks for folder redirection
Considering folder redirection
VDI user profile management secrets
Protecting user data in a virtual desktop environment
Organizations that choose to rely solely on folder redirection typically enforce a mandatory user profile. In other words, the virtual desktop settings are static. A user can make changes -- he can create a desktop shortcut or change the wallpaper, for example -- but these types of changes are not session persistent. When the user logs out, the desktop will be reset to a pristine state.
There are a couple of advantages to using this approach over profile redirection. Storing user data is centralized with folder redirection, which means data is stored independent of the individual virtual desktops. More importantly, centralized data storage makes it easy to back up user data.
It might seem that this approach would be far less bandwidth-intensive than redirecting an entire profile directory, but when you redirect a folder, Windows automatically copies the folder contents to an offline cache at logon. The offline cache makes user files accessible even if network connectivity is lost, and the copy process does dramatically increase the amount of time that it takes the user to log on.
Microsoft has made some improvements over the last couple of versions of Windows to address this problem. For instance, in Windows 7, Microsoft introduced a background copy process that allows the end user to log on much more quickly. Even so, the copy process still made folder redirection bandwidth intensive. In Windows 8, Microsoft finally provided a Group Policy setting that lets you disable offline files for redirected folders, which goes a long way toward reducing bandwidth consumption. While it is true that disabling offline files eliminates the local cache, the cache is unnecessary in environments with reliable network connectivity.