Can persistent and pooled virtual desktops have the same cost? Storage Spaces for Dell Wyse Datacenter for Microsoft VDI and vWorkspace is the answer

In a recent blog post, we discussed how deploying persistent virtual desktops was not out of reach even under current economic conditions. After all, when using a traditional iSCSI Storage Area Network (SAN) on Dell hardware and Microsoft Windows Server 2012 R2 Hyper-V, your users can have all the benefits of a persistent virtual desktop for only about 15% more per user (+$50 per user in most cases) than the cost of deploying pooled (non-persistent) virtual machines (VMs). In that example, 600 Standard users1 can have a persistent VM for as little as $400 per seat2 using a Dell Reference Architecture with an EqualLogic SAN and the Microsoft deduplication features built into Windows Server 2012 R2 (see also Figure 1 “Using as SAN”).

Persistent VMs can cost the same as pooled VMs

In the last three months, Dell has significantly enhanced its Dell Wyse desktop virtualization solution that leverages Microsoft Windows Server 2012 R2 Hyper-V. To improve our Dell Wyse Datacenter for Microsoft VDI and vWorkspace solution, we first qualified better optimized servers (R420, R620) to act as new management host and file servers, further reducing the cost of the overall solution without impacting performance. Next, and more importantly, we enabled our solution to support Microsoft Storage Spaces. This feature allows your IT department to now deploy persistent VMs at the same cost as pooled VMs, starting at under $350 per seat. This price is based on a deployment of 600 Standard users1, assumes three years depreciation and include datacenter hardware, software and licensing excluding only VDA licenses and end points2.

To achieve this, we replaced a SAN with a more affordable Direct Attached Storage (DAS) enclosure such as the Dell PowerVault MD1220 using a JBOD (“Just a bunch of disks”) and commodity hardware architecture and implementing Microsoft Storage Spaces. The full benefit is achieved by adding a Storage Spaces File Server (SS FS), such as the Dell PowerEdge R620. This server, designed for performance, is optimized for managing hot and cold data (read below about Storage Tiering for a definition), along with open VHDs (for post-process deduplication), which is a fairly CPU-intensive job.

The different datacenter elements are shown in figure 1, comparing the cost per seat of VDI solutions implemented with a SAN vs. a DAS with Windows Server 2012 R2 Hyper-V. Even using a less expensive DAS, the storage element remains a critical part of the investment, requiring usage optimization by maximizing the number of virtual desktops it can support, coupled with the server user density. We have determined that one Dell PowerVault MD1220 can support up to 1000 Standard users1 or 700 Enhanced users3 with 15,624 physical IOPS. The technical aspects of this implementation were recently presented at TechEd.

This solution with Storage Spaces on the MD1220 significantly lowers the storage costs associated to a VDI deployment and greatly simplifies decision making in your organization. All you need to ask yourself is:

1)    How many virtual desktops do you want to deploy initially? (regardless of being pooled or persistent).

2)    What “profile” or VDI workload do you need for your users? This determines how many users you can run per compute host server. You can break up your user base into three identifiable workloads: Standard (for task workers), Enhanced (for office worker), Professional or Shared Graphics (for most demanding power users).

You no longer need to factor in potentially complex storage considerations associated with persistent virtual desktops. You can later decide which users get a pooled or a persistent virtual machine. Because they cost the same, you might as well assign persistent VMs to the majority of your users. This will greatly enhance their end user experience and boost the chances that your VDI pilot deployment will succeed within your organization. Indeed, with persistent VMs, your users retain a more traditional physical PC experience with customizable options and settings, the ability to install approved applications, retain their active directory identification and My Documents folders, following reboots, and install their personalized wallpaper.

Our Dell PowerEdge R420 server allows you to start small with a pilot with as little as 50 Enhanced users. Later, as you decide to expand VDI throughout your organization to hundreds or thousands of users, you simply add additional servers and storage arrays as the solution scales almost linearily.

What is Storage Spaces?

Microsoft Storage Spaces is a Software Defined Storage (SDS) technology included with Windows Server 2012 R2. This technology allows you to save money by using a DAS enclosure in place of a SAN within your desktop virtualization deployment. Storage Spaces technology uses SAS HBAs (Host Bus Adapters) and standard disk arrays to provide highly available and resilient storage for hosted and virtualized deployments. Storage Spaces is based on a disk pooling model. Storage pools can be created flexibly, further keeping a ceiling on your initial investment by using affordable commodity hardware, depending on the needs of the deployment. A storage space integrates well with the rest of the feature set available in Windows Server 2012 R2 like failover clustering for high availability. This ensures that Storage Spaces can provide a cost-effective platform for business critical storage across a variety of scenarios. Finally, you can also implement storage tiering, which automatically optimizes the location of the data in the volume so the most frequently accessed data (“hot data”) is on the fastest disks in the solution (e.g. SSD), and the older and less-frequently-accessed data (“cold data”) is moved to slower, cheaper HDDs (e.g. SAS disks).

In its latest reference architecture for Dell Wyse Datacenter for Microsoft VDI and vWorkspace solution, Dell has recently qualified its desktop virtualization infrastructure stack on Microsoft Storage Spaces and deduplication, with the inclusion of an additional Storage Spaces File Server. This file server runs Windows Server 2012 R2 for both the tiering and deduplication activity with the PowerVault MD1220 JBOD array.

As shown on Figure 2, Hyper-V clusters communicate with the SS FS via Microsoft’s SMB 3.0 protocol and the SS FS is attached to the PowerVault DAS.

With Dell Wyse Datacenter for Microsoft VDI and vWorkspace, you can deploy very affordable persistent VMs; you can also implement unified communication with Lync and shared graphics cards for your most demanding users. If you later decide that you want to use the optional Dell vWorkspace virtualization software, you can scale up with ease to hundreds or thousands of users, and enjoy a considerable operational cost savings by using the unique built-in diagnostics and monitoring feature (formerly Foglight for virtual desktops).

For more information, read the reference architecture for Dell Wyse Datacenter for Microsoft VDI and vWorkspace and try the cloud client-computing advisor tool to get a BOM in minutes followed by a quote within a day. Visit or contact us to learn more.


1 Standard user: corresponds to a simple task worker workload in which the user of the VM works typically with a repetitive application. Sample use cases may be a kiosk or call-center which do not require a personalized desktop environment and the application stack is static. The workload requirement for a basic user is the lowest in terms of CPU, memory, network and Disk I/O requirements. You can run up 225 Standard users on one PowerEdge R720 compute server. You can find detailed information here in section 7.1.2.

2 Based on May 2014 Dell US list price for a calculation optimized for 600 Standard users, including PowerEdge R720 servers, EqualLogic PS6100XS SAN (for persistent VMs, in a shared tier 1 mode) or PS6100E (for pooled VMs, in a local tier 1 mode), PowerVault MD1220 DAS enclosure, Dell Networking S55 1GbE switch, 3 years Dell ProSupport, Warranry, Windows Server 2012 R2 licenses and 600 RDS CALs. Amortization is over 3 years. It excludes end points, VDA licenses and vWorkspace software.

3 Enhanced user: corresponds to a knowledge worker with a medium VDI workload in which the user of the VM works with email, typical office productivity applications and web browsing for research/training. The workload requirement for an Enhanced user is moderate and most closely matches the majority of office worker profiles in terms of CPU, memory, network and Disk I/O. It can be considered similar to a physical desktop replacement. You can run up 150 Enhanced users on one PowerEdge R720 compute server. You can find detailed information here in section 7.1.2. 

About the Author: Nicolas Cuendet