Software as a Service vs. desktop virtualization solutions

Learn the pros and cons of Software as a Service and desktop virtualization as application delivery solutions. Find out which technology requires more maintenance and compare their costs.

By Stephen J. Bigelow, Senior Technology Writer

Software as a Service (SaaS) or desktop virtualization: Which solution is better for your customers?

These technologies are clearly different, but they both involve the delivery of applications to end users, which affects the way customers handle their everyday business. Solutions providers must weigh the pros and cons of SaaS and desktop virtualization solutions and select the technology that best meets customers' business goals. This article compares the two approaches and outlines the factors to consider when preparing a recommendation.

Understanding SaaS and desktop virtualization

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The virtual desktop infrastructure (VDI) approach to desktop virtualization consolidates processing workloads. A virtual desktop running on a server in the data center handles the workload that's traditionally processed on PCs.The server, in addition to handling SAN storage, provides all of the resources needed to execute applications. This approach reduces the role of the endpoint to that of a dumb terminal.

With a desktop virtualization solution, application delivery still follows the single-PC paradigm. Programs -- along with their patches and upgrades -- still need to be purchased, installed, stored and supported for each virtual desktop.

By comparison, Software as a Service solutions deliver applications to users from a central location. There are two typical approaches to SaaS. In the hosted application model, which is similar to the concept of application virtualization, a provider hosts the application on a server and allows users to access the application across a network. The on-demand SaaS model gives users access to an application as needed, and users pay for the time they use it. Regardless of the approach, a SaaS application represents a single deployment that administrators can patch and upgrade at a single point.

SaaS vs. desktop virtualization

It's important to point out that Software as a Service and desktop virtualization are not mutually exclusive solutions. Either or both technologies can be appropriate depending on each customer's particular needs and capabilities. The trick for solutions providers is to choose the most suitable approach for each customer by focusing on three factors: complexity and cost, endpoint requirements and maintenance, and reliability.


Complexity and cost


Desktop virtualization is more complex than Software as a Service. It adds another layer of abstraction -- the virtualization operating system or hypervisor -- and increases requirements for server CPU, memory, and I/O, as well as storage. The move to desktop virtualization can reduce desktop support and endpoint replacement costs over time, but many small and medium-sized businesses simply can't afford the new servers and storage, network upgrades and other startup costs of a desktop virtualization deployment.

Third-party application service providers (ASPs) typically implement SaaS, but it is possible for customers to host their own applications in-house. Either way, users access SaaS applications through a Web browser, which introduces no complexity or overhead costs. The ASP is responsible for the costs of hardware infrastructure, software licensing and maintenance, and the customer only rents these services. In addition, customers can easily adjust the number of applications they need delivered and the number of users who need access to those programs.

The downside is that SaaS uses a subscription payment model, and customers can find themselves locked into service agreements with ASPs for fixed periods of time. The total cost of SaaS can eventually become substantial.

Desktop endpoint requirements and maintenance

The endpoint hardware requirements for desktop virtualization and Software as a Service solutions are extremely low and not a substantial concern in most situations. Desktop virtualization needs only a dumb terminal at each endpoint, and SaaS generally requires an endpoint capable of running a Web browser. Almost any current PC or thin client is suitable for either approach.

Solutions providers should consider endpoint maintenance before recommending either SaaS or desktop virtualization. With desktop virtualization, all virtual machines are on servers in the data center, and administrators can update software or make changes to all virtual desktops from a central point. When a hardware fault occurs, admins can replace the endpoint device with another PC or thin client without having to reload or restore user settings.

When running SaaS solutions, however, endpoint maintenance is more demanding. Each endpoint needs repair in the event of a failure. And when a PC is replaced, admins must recover and restore all user data to the new PC.

Reliability of SaaS and desktop virtualization


Consider the effects of service disruptions on customers' business operations. With desktop virtualization solutions, data center servers determine reliability, and a server fault will disrupt the endpoints running on that server. Many solutions providers opt to spread desktop virtualization out across multiple servers, such as blade servers, or to deploy server clusters to improve resilience. When trouble does strike, corrective action is typically handled by in-house IT staff or solutions providers responsible for maintenance.

The reliability of SaaS solutions can be a bit more problematic. Unless customers host the applications themselves, they must rely on the ASP's infrastructure and the WAN or Internet to connect everything. A failure by the ASP or the customer's Internet service provider can render SaaS applications inaccessible, and it's something that solutions providers and their customers have no direct control over. Customers that rely on SaaS for mission-critical business applications will need to tolerate this higher level of risk.

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