Server-hosted virtual desktops are gaining popularity to meet several business challenges. Companies are leveraging VDI solutions to simplify operational support as the industry moves from a device centric deployment model to a user centric deployment mode. This, in part, is being driven by senior level management and sales teams that want to use devices like tablets and ultra-books when they are on the road. Also, VDI solutions are being leveraged for the externalization of technical support and to secure business information in the data center. Common examples for implementing a server-hosted virtual desktop solution include enterprise desktop replacement, remote user access, corporate acquisitions, outsourcings, and disaster recovery planning.
Although there are several key factors driving organizations to adopt VDI deployments, the capital costs have made the acceptance slow. 40% to 60% of the cost of a VDI implementation is related to storage infrastructure. We are going to look at VMware’s reference architecture to implement a stateless VDI architecture that uses high performance local solid-state drives in the host servers instead of the storage array to reduce costs and improve performance.
This design isn’t for everyone, but it can reduce capital costs if you are deploying stateless desktops for call centers and kiosks.
Linked ClonesVMware View with View Composer uses the concept of linked clones to quickly provision virtual desktops. View Composer uses a parent image to create a pool of linked clone virtual machines. A parent image is a tuned desktop that will be used to create new replica images. Each linked clone acts like an independent desktop, with a unique host name and IP address, yet the linked clone requires significantly less storage. All files available on the parent at the moment of the snapshot continue to remain available to the linked clone. The operating system reads all the common data from the read-only replica and the unique data that is created by the operating system or user, is stored on the linked clone.
Solid-State ArchitectureStateless architectures have many advantages, such as being easier to support and having lower storage costs. The virtual desktop is typically deleted or refreshed after each use, offering a highly controlled environment. Because we are using solid-state disks local to the hosts, the virtual desktops will be stateless; they will be a member of a floating-assignment pool of linked cloned virtual desktops. The nature of these desktops is similar to a kiosk environment, except we are going to leverage persona management to personalize the user experience.
View Persona ManagementWith VMware View 5, VMware introduced View Persona Management. View Persona Management facilitates implementing a floating-assignment pool for those users who want to retain settings between sessions. It preserves user profiles and dynamically synchronizes them with a remote profile repository. Previously, one of the limitations of floating-assignment desktops was that when end users logged off, they lost all their configuration settings and any data stored in the View desktop.
Each time end users logged on, their desktop background was set to the default wallpaper, and they would have to configure each application's preferences again. With View Persona Management, an end user of a floating- assignment desktop cannot tell the difference between their session and a session on a dedicated assignment desktop.
Sizing storage for VDI is one of the most complicated and critical components during the design and implementation process. Because we are leveraging local SSD, the replica and the OS data need to stay together. Unlike tiered storage in the SAN array, it can’t use a Dedicated Replica Datastore for the read-only replica base image. This means the storage footprint in the local solid-state drives needs to stay very small to provide capacity for the replica base image and the linked clones.
The user profile data and home directories can be stored on 7.2k near-line SAS disk, while the replica base image and linked clones will be stored on the local solid-state drives. Replica disks are created as thin provisioned clones from the Parent Image. If the Parent VM has 50 GB allocated and 30 GB consumed, then the replica disk is equal to the amount of utilized storage which is 30 GB. In order for this to work, it is recommended that you have a basic parent image for your deployment that uses memory reservations to minimize the disk footprint. If your swap and video swap file are too large, then this architecture will require larger SSD drives than your host may accommodate. I suggest that you use the VMware View Optimization Guide for Windows 7 to tune your Parent image.
The formula for calculating your capacity is the parent image + replica disk + delta disks. You calculate your delta disks by (VMs per datastore *(delta size + swap + video swap + suspend + log) +10% overhead). If you set your Refresh OS Disk on Logoff to Always, the OS disk is refreshed every time the user logs off and it should remain relatively small, I would plan for 512 MB to 1 GB in size for the delta.
Infrastructure ResiliencyIf a host, drive, power supply or similar component fails; the high-level design provides the redundancy necessary to provide a user with a new desktop. A stateless design has different requirements for high availability compared to traditional virtual desktop deployments. In the past, redundancy designs would be based on advanced virtualization features within vSphere like High Availability (HA), Distributed Resource Scheduling (DRS), and live migration with vMotion. With stateless usage of the local datastores, these features are no longer needed.
Why aren’t they required? The reason they aren’t required is because the failure of a host is seen by the VMware View Connection Servers. In the case of a server failure, the broker will simply allocate a new desktop for the user after successful authentication. View Persona Management will facilitate moving the user settings to the new session.
Careful planning of the pools needs to be considered. You need to make certain you have enough overhead the pool to ensure there is capacity for a host failure. If you are deploying 300 virtual desktops over 4 physical hosts, you need to add 25 additional desktops per host pool to support the resiliency necessary to ensure all the desktops are active after a node failure.
A successful server-host virtual desktop deployment enables businesses to deliver virtual desktops to multiple devices while securing company data in the data center. Storage is a critical component to the success of any VDI deployment. From a user’s perspective, good performance of a virtual desktop is a lossless experience as they transition from a physical device to a virtual desktop. Therefore, the correct way to implement a storage design is through careful planning that maximizes performance and balance out cost.
VMware’s reference architecture to implement a stateless VDI environment with local solid-state disk is a great solution for call centers and kiosk environments, but a more robust solution is needed for environments that are using their server-hosted virtual desktop infrastructure for knowledge workers and power users.