How To Assess the Cost of Implementing VDI
Unfortunately, a proof-of-concept rarely reflects the true cost of taking a new solution into production. Given the many moving parts that a VDI implementation can involve, there is strong potential for unexpectedly high infrastructure costs and complexity.
In this post, I will outline how to scope and assess VDI projects, so that initial costs are included, as well as what will be needed to help users scale, provide high availability, and manage the system.
In selecting a VDI solution, make sure to have a detailed, informed conversation with your vendor to fully understand the real costs of the implementation both up-front and over time. The vendor should be able to provide concrete figures based on a TCO or ROI calculator; while these will always be estimates rather than guarantees, they will provide valuable information to help evaluate options and make the best choice.
The cost assessment process should include the following areas:
Virtual Desktop Host Servers
How many servers are necessary to run the virtual desktops for users? This should be a straightforward calculation based on the number of virtual machines than can be run on each host, and the total number of users in any given environment. Ask the VDI vendor for a sizing guide with their recommendations on density based on the types of virtual desktops you plan to run (e.g. for task workers using basic Office applications vs. power users who may need lots of graphics capabilities).
If the solution being evaluated requires shared storage, i.e. a SAN, it will be necessary to estimate the cost of both the SAN and the related high-speed interconnects typically required for their production usage. This can be quite expensive, and also has implications for scalability--as users scale, they will not only need to add more SAN capacity but also increase the interconnect speeds to account for factors such as boot storms. On the other hand, a solution that leverages off-the-shelf, direct-attached storage (DAS) will usually prove much less expensive both initially and over time. If the solution uses DAS, ensure that it will still provide high-availability so end users will have business continuity in the event of a server failure.
Traditional VDI architectures require organizations to install separate connection brokers, provisioning servers, load balancers and sometimes clustered SQL servers as well. Work with the vendor to determine how many servers are required to run these components, and add their cost to your estimate. You also need to consider the cost of any Microsoft and other software licenses needed to run on company servers.
One way to avoid these costs is to base the VDI implementation on a shared-nothing architecture, which eliminates the need for management servers (as well as the need for a SAN). For example, the Citrix VDI-in-a-Box software appliance integrates connection brokering, desktop provisioning, load balancing and user profile management and lets users connect servers so they comprise a highly available grid which balances loads automatically. All that's required are the virtual desktop host servers.
Though often omitted from proofs-of-concept, high availability is a critical element of any VDI implementation designed to increase availability and make sure users don't lose access to their virtual desktops.