As this chapter already mentioned, RDS provides one platform to deliver desktops by using multiple methods, including:
1- Personal VMs Personal VMs give users access to a dedicated, high-performance desktop over which they have full administrative control.
2- Pooled VMs Pooled VMs give users access to high-performance desktops from connected devices. RDS assigns VMs on-demand from an existing pool to users. When they log off a VM, RDS returns the VM to the pool for another user.
3- Session-based desktops Session-based desktops provide access to applications, data, and shared desktops that are centralized in the data center.This is the typical terminal services approach to virtualization a desktop.
NOTE With pooled VMs and session-based desktops, users can still personalize their experiences considerably, although they still cannot install applications. Roaming user profiles and folder redirection are still available, but RDS adds support for user profile disks.With user profile disks enabled, RDS mounts a virtual hard disk containing the user’s settings and data to their user profile folder (C:\Users\Username).User profile disks persist between sessions.A great thing about user profile disks is that they are very simple to set up and manage.
RDS powers all three Microsoft VDI deployment methods, and they all have common benefits.They provide powerful administration features through the built-in management console (Figure 11-2).They offer a powerful and scalable virtualization platform, regardless of whether you are deploying session-based desktops, pooled VMs, or personal VMs. Lastly, they give users a consistently rich experience across LAN and WAN.
Regardless of their common benefits, your choice depends on the following points, and Table 11-1 summarizes them for easy comparison:
1- Personalization Do users need the ability to customize their desktops? If so, what level of customization do they need? With session-based desktops and pooled VMs, users have limited personalization capability with user profile disks (i.e., the ability to persist their data across different logins). However, they cannot keep their user- installed applications across logins. On personal VMs with administrator access,
users can change any aspect of their desktop, including installing applications that persist across multiple logins.
A-- Application compatibility Session-based desktops share a common server operating system; therefore, any applications that are to be installed need to be compatible with Windows Server 2012. In both VM scenarios, however, Windows 8 is running in the VM. So application compatibility is always higher for VMs.With personal VMs, users can install their own applications, but you decide what applications to install on pooled VMs. As a result, personal VMs provide the highest level of application compatibility across all three deployment methods.
B-- User density Because session-based desktops share a single server operating system, the number of users that a single server can accommodate is always going to be higher than either VM scenario. With pooled VMs, because user data is not stored locally (but can be stored on a separate user profile disk), the sizes are typically smaller than personal VMs.As a result, pooled VMs have slightly higher density. You can improve the density of pooled and personal VMs by using user state virtualization and application virtualization technologies on the VM, but they will always have a lower density than session-based desktops.
C-- Image count If maintaining a single image is important, the best way to achieve that goal is through session-based desktops or by deploying pooled VMs. In a session-based desktop, all users share a single server image. With pooled VMs, all users use a cloned copy of a single master image. Single image configurations are easier to manage and have lower costs in comparison to personal VMs, in which each user uses an individual image.
D-- Cost Because session-based VDI offers the highest densities and a single image, it is usually easier to manage, so it offers the lowest cost. Pooled VMs have the single image and management benefits of session-based VDI, but reduced densities and increased management effort means that they are more expensive to deploy. Personal VMs have the lowest density and highest management efforts, making them the most expensive deployment method. However, Windows Server 2012 helps organizations reduce overall costs for VDI with support for lower-cost storage (e.g., SMB and DAS), application virtualization, dynamic memory, and user profile disks.
"Computer Tips: Choosing the right VDI deployment in Windows 8"
Reference : www.microsoft.com