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Desktop hosting basics: Defining VDI and DaaS

Desktop hosting might mean deploying VDI in your data center, or it might mean throwing those desktops to the winds of the cloud.

Desktop hosting strategies such as VDI and DaaS have come to the forefront of enterprise desktop management, and each shop has to decide for itself whether to host desktops in the cloud or on-premises.

From analyst blogs, it seems clear that all of IT is moving to cloud and mobile computing. This is also the marketing position we see from Amazon, Google and even Microsoft. The business reality, however, is that most organizations do not run solely on Apple iPads and cloud services -- Windows applications are a fact of life for the majority of businesses.

For more than 20 years, developers have written apps for Windows, which means IT needs to provide staffers with Windows computers. From beige boxes to laptops and now tablets, most Windows apps run on computers that their users can touch.

At the same time, it is possible to separate software execution from the user interface. Products from Citrix, Microsoft, VMware and a host of other vendors allow Windows applications to run on one computer and display on another.

VDI and desktop as a service (DaaS) put programs in the data center and let workers choose which endpoint devices they use to run them. Similar to the way workers can use a browser to accesses a Web server over a network, they use VDI clients to access desktops over a network.

IT shops must decide whether to host desktops in their own data centers through VDI or in a service provider's data center through DaaS. To make that decision, it's important to know how VDI and DaaS are different, as well as how they are similar. It is also worth knowing why organizations choose one desktop hosting method over the other.

What are VDI and DaaS?

In VDI, a screen and keyboard remain on the user's desk, connected to a client, but his or her applications run in the data center. Most often, user desktops each run in their own virtual machines (VMs) on a hypervisor, allowing many users to share a single physical host. Other options include a dedicated physical workstation in the data center for each user, and Windows Remote Desktop Session Host servers that multiple users can share.

Once users' virtual desktops run in the data center, they may use a VDI client on nearly any other device to access them. Note that VDI usually requires its own access infrastructure and a virtualization platform.

VDI deployments have been described as an iceberg of complexity. Poking up above the water are the connection broker, the VDI client and a few desktop VMs. Hiding below the surface are the many layers, such as the hypervisor, storage array, network, user accounts, user persona, file sharing, application deployment, VM provisioning and patching. This long list is a combination of the entire virtualization infrastructure and all the components necessary for well-managed physical desktops.

At anything but the very smallest scale, VDI requires specialized skills to design, deploy and operate well; poor management isn't an option. A storage array that doesn't deliver the required performance, for instance, could result in multiple staff complaints about how long it takes to log in. Connection brokers that are unexpectedly offline for patching will prevent anyone from logging on. VDI may only deliver a desktop, but it's mission-critical because it involves every desktop.

DaaS, on the other hand, is a desktop hosting method that moves the user's desktop onto virtualization hosts in a service provider's data center. Essentially, a DaaS provider builds a huge VDI environment and rents virtual desktops out to customers.

Some people also think of DaaS as a desktop in the cloud, where the National Institute of Standards and Technology cloud definitions apply: self-service, elastic, pooled and customers only pay for usage, not necessarily potential processing capacity. Customers choose how many desktops they want in a particular month, and they are only billed for that number of desktops.

For example, a company can decide that it wants an extra thousand desktops for a month, and at the end of the month, it hands them back to the service provider. The customer only pays for the month's use of the extra desktops.

Providers have a large pool of processing capacity to run desktops for multiple customers, gaining economies of scale for purchasing, deployment and management. This allows for more instant scalability, or elasticity than a dedicated VDI platform. Providers also benefit from averaging the demand over their customers.

Achieving an agile desktop

Desktop hosting methods such as DaaS and VDI allow much more flexibility and agility than the standalone laptops and desktops that they usually replace. Employees can access virtual desktops from different locations, while a desktop sits on a desk and can only be used from there. Staffers can access the same desktop environment with the same applications and data access as they go about their day.

Workers can use thin clients at their desks, move to tablets in a meeting and access the same desktop from their home PCs to finish off a report after the kids have gone to bed. A new virtual desktop can usually be provisioned in minutes, rather than the days it takes to get a new PC.

In addition, a virtual desktop is very connected; it is in the same data center as all the servers, unlike a laptop, which must access a lot of data and services remotely. VDI and DaaS also help make a user's client device expendable because it has no data and needs minimal configuration. If a user's primary access device fails, gets lost, or if they leave it at home, there are a few other devices they can use instead.

A VDI or DaaS desktop lets staff members work in different ways and from different places, potentially making the staff more productive and valuable.

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