What's VDI? Is It Right for Your Firm?

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By Jonathan Hull, Xcentric 

Virtual desktop infrastructure (VDI) is a hyped term in the technology market right now. Unfortunately, the term has really become ambiguous, as VDI is more of a concept than a technology. VDI actually encompasses a suite of different technologies; therefore, it's important to distinguish between what's being delivered and how it's set up.

What is VDI from a high-level perspective?

The industry has had a hard time defining terms. VDI is an umbrella term for many technologies put together. As a concept, VDI delivers desktops, applications, operating systems, and data to end users. VDI generally encompasses desktop virtualization, which separates the PC desktop from a physical machine, but you can have desktop virtualization without VDI. For example, a published terminal services desktop is also considered desktop virtualization; however, VDI is generally associated with hosted virtual desktops (HVDs), while a published terminal services desktop is associated with server-based computing (SBC), two very different technologies.

There are companies that perform remote desktop solutions on a one-to-one basis and call it VDI. For instance, if someone were to deploy a 1,500 user device, it would take 1,500 pieces of hardware to deploy. In this case, no virtualization actually takes places because they're accessing a physical desktop. Although, this is technically a form of VDI, it's a very clunky one. VDI can be optimized in a ratio like 1,000 to 1 instead. That is, where you have 1,000 users using thin clients that give them access to a single virtualized desktop. A thin client is when someone is using a computer that relies heavily on another server or computer. In this case, you don't need a physical desktop for each remote desktop.

Who are the main vendors?

A hypervisor is a foundational layer that virtualizes the desktop. There are three main vendors that provide hypervisors to the VDI market: VMware, Citrix, and Microsoft. VMware offers what's called VMware view. VMware view allows you to customize the desktop by virtualizing and delivering a single image model where a gold master is used for a base image of the desktops. The base operating system and applications are the same, so that a single image is rolled out to all users. Citrix has a similar structure called XenDesktop with the HDX protocol, and Microsoft offers Hyper-V with the RDP protocol.

How does a VDI work?

To virtualize a desktop, an enterprise must make its desktop environments configurable, deployable, and manageable from a central location. All VDI deployments start with provisioning a desktop to an end user, whether it's a physical or virtual desktop. The next step is to install a piece of software, called an agent, on top of the desktop, which will enable access to the virtual desktop. Each VDI vendor has a different protocol for how the communication takes place to gain access to the virtual desktop. Once enabled, the thin client desktop connects to a configured user disc image in either a shared or persistent desktop, and a broker determines who gets access to what desktop. The connection broker is similar to a mortgage broker for business loans in that it lies at the heart of any functioning VDI. A broker ties all the pieces of VDI together and makes the decision as to who can access what data and how. How do shared and persistent desktop configurations differ? Let's take a look.

When a shared desktop environment is created, it meets the needs of all end users and an image is shared across the organization. This works best in an enterprise environment where common applications meet the needs of task workers inside the organization. Xcentric uses this concept when provisioning servers, and it can also be applied to shared desktop virtualization.

If you have anything that deviates from the shared desktop environment, where one or more shared images don't meet all the needs of your end user, then you have to introduce what's called application virtualization. This is where applications are streamed, run into an isolated environment, and show up for a single user. Basically, a custom fit or a one-off.

Whether or not a CPA firm is a good fit for VDI depends on the firm's environment. Applications drive all of this, and user environment management is an important aspect to evaluate. If you have a shared desktop and need to personalize it, the question becomes how to persist the data. Persistent data structure is where the previous version of the data is modified while maintaining the previous version. There are companies that specialize in customization of user data, such as RES Software, Unidesk, and App Sense. These companies persist user environments by personalizing desktops and delivering the applications that each user requires to work. This is another technology that fits inside the concept of VDI, called a persistent desktop. In the case of a persistent desktop, there's a one-to-one mapping of a desktop to a user, meaning each user gets a unique desktop image that must be maintained and managed by the broker. With this method, all of the data from every unique desktop must be stored, which necessitates much larger storage requirements. Ultimately, the available options are shared desktop, persistent desktop, or marrying the two with what's called application virtualization.

What are some VDI scenarios?

  • Scenario 1: A business gives each employee a desktop with a VDI agent installed on the desktop so that employees can connect remotely; similar to GoToMyPC.
  • Scenario 2: Start out with a hypervisor (either VMware, Citrix, or Microsoft Hyper-V) and give people remote access to a virtualized desktop. This way, the hardware stays centralized while the desktop becomes virtual.
  • Scenario 3: Using Citrix, the client can install a hypervisor on a laptop, which can react to things like wireless and closing the lid.

If not VDI, then what?

  • Terminal services environment. Functional and mature; we use it here at Xcentric.
  • Traditional desktop. With this option, application virtualization can also be used, and the OS doesn't need to be virtualized.
  • Kaviza. This is more for the SMB market; however, Citrix just bought a Kaviza solution, which is an appliance that users can connect to for their desktops without needing all shared storage or user provisioning; just add more appliances as you grow; you'll need a bunch if you're a really big environment. They use HDX as their remoting protocol.

Xcentric hasn't pursued VDI for a couple of reasons:

  1. There's no Microsoft Service Provider License Agreement (SPLA) for VDI, meaning we would have to purchase perpetual desktop licenses along with a service agreement for each desktop license. This alone would break the bank.
  2. User density with terminal services-based solutions (i.e., Citrix XenApp) is much greater than desktop virtualization. With VDI, we would have to quadruple the amount of hardware we have today to support the same amount of users. Note: This quadruple statement is true for us in a remote disconnected data center environment and may not apply to everyone.

It turns out a lot of companies that have tried to go down the VDI route are putting on the brakes beyond pilots. People have become disillusioned by what VDI will do. For instance, VDI is not always a cost savings. In the case of persistent desktops, there are hidden storage costs because you're creating a unique user profile and storing the data for each end user. Input/output operations per second (IOPS) are used as a performance measurement to find the best storage configuration. Setting expectations on network capabilities and storage costs is a must.

Final say

There's no definite answer on VDI, as the answer is unique to every firm. VDI is not a one-size-fits-all solution. For instance, VDI is an easier fit in the education, manufacturing, and medical arenas because these are more task-driven environments. Similarly, VDI may be a "slam dunk" for a niche function inside a CPA enterprise but may not be across the entire organization. If VDI is something you want to consider, we recommend considering real-life cases that have worked for other CPA firms in the past. The more facts you have, the better you're able to make a decision.

About the author:

Jonathan Hull is an account manager at Xcentric, an IT solutions company that provides hosted and managed technology platforms for the accounting profession.

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By Nate
Jun 26th 2015 01:10

Good article. The first line couldn't be more true. We have a small cpa firm near us that praises his firms move to vdi. Employing only 5-7 people vdi seems to work well for them. He constantly praises and tells our shareholders that we should do it (35-40 employees) Doing some top level research just on file storage for profiles, loses in Outlook functionality and accounting apps that won't play well with vdi requiring persistent disks and application visualization. We'd also need 4 time more server hardware no difference in licensing, and a lot of new expensive software but possible a drop in user satisfaction. I'm having difficulty justifying vdi. I will say if you have pc's that are utilized for 1 thing, look into virtualizing it, not vdi, just hosted on a hypervisor.

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