Probably the biggest challenge for a virtual desktop infrastructure (VDI) to succeed is its infrastructure impact and cost. With desktop and laptop prices starting at $500, plus intangible management costs, any ROI for VDI needs to weigh the obvious benefits against the cost and effort it takes to acquire and maintain a data center infrastructure that can support hundreds and possibly thousands of virtual desktops.
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VDI comprises several joined components that enable clients to run their desktops remotely from within the data center:
- A hypervisor, such as Citrix Systems Inc.'s XenServer, Microsoft Corp.'s Hyper-V or VMware Inc.'s ESX Server, which runs on a server and executes the desktop virtual machines.
- A management platform offered by the hypervisor vendors for their respective products. This manages the hypervisor servers as well as the pool of virtual machines (VMs) used by existing connections and requested by new connections, and facilitates provisioning desktop virtual machines to VDI clients.
- A session broker that's responsible for distributing sessions from clients to VMs and redirecting users of disconnected sessions back to their original virtual machines.
Data storage requirements
To start, VDI requires servers to run the desktop VMs. With one CPU core able to support about five users, according to Brian Gammage, a vice president/Gartner fellow who covers client computing, a typical eight-core server can support approximately 40 users. VDI requires network storage for desktop virtual machine images and user data. By simply moving desktop images from clients to servers, and with the average desktop image requiring approximately 10 GB of storage, 100 virtual desktop images consume 1 TB of relatively expensive network storage vs. the low-cost disks used in contemporary desktops and laptops.
Even with offline support, VDI depends on a reliable network and sufficient bandwidth on both the local-area network (LAN) and wide-area network (WAN), and the larger the VDI deployment the more likely network upgrades will be required. Add to that the cost of cooling, electricity and data center space, and it adds up to a significant IT infrastructure investment. On top of that infrastructure investment, there's the cost of the virtual desktop software, typically licensed by concurrent desktop (VMware View) or concurrent user (Citrix Systems XenDesktop), OS licenses, as well as the Microsoft Vista Enterprise Centralized Desktops (VECD) add-on license Microsoft demands for each VDI client in addition to the OS license.
Vendors working to minimize hardware requirements
The cost of getting a virtual desktop infrastructure off the ground is truly staggering, and VDI software vendors have been working feverishly to minimize hardware requirements, especially those related to storage. They're also partnering with server, storage and networking vendors to maximize the number of virtualized desktops their devices can support by adding features like data deduplication and thin provisioning to storage arrays, and enhancing servers to increase the number of concurrent VDI sessions the servers can support. One example is Cisco Systems Inc.'s Unified Computing System (UCS) server platform.
"While a normal server blade can support about 40 to 60 VDI clients, UCS more than doubles that number, effectively reducing the cost per user by more than a factor of two," noted Chad Sakac, vice president of the VMware Technology Alliance.