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Without an effective VDI hypervisor, IT may encounter performance, availability, scalability and management issues.
The hypervisor, which abstracts physical resources and delivers them to users through one or more VMs, is at the heart of any VDI deployment. When IT considers hypervisors, it should evaluate what platforms the hypervisor supports, how IT can secure and manage the hypervisor, how the hypervisor delivers desktops, and the total cost of ownership (TCO). Only then can IT ensure that the hypervisor it selects will meet its requirements now and in the foreseeable future.
An important consideration with any hypervisor is the platform it will run on. For example, the Xen and KVM hypervisors both use the Linux kernel, so they're limited to Linux hosts. Microsoft Hyper-V is available only with Windows Server and Hyper-V Server, which means committing to Windows desktops.
The hardware that hosts the VDI hypervisor is also important. Xen can run on x86, x86-64, Itanium and advanced RISC machine architectures, while VMware ESXi has stricter hardware requirements that limit it to 64-bit x86 servers. Organizations that have already invested in potentially incompatible platforms must take their existing systems into account when evaluating hypervisors.
Another important consideration is which guest OSes the hypervisor supports. Hyper-V can run Windows Server 2008 through 2016, Windows 7 through 10, several Linux distributions and FreeBSD. ESXi supports all of these OSes, plus older Windows versions, additional Linux distributions, MS-DOS 6.x, Novell NetWare Server and Oracle Solaris.
IT teams should also consider any other platform-related factors that might play a role in delivering virtual desktops, such as dependence on a cloud infrastructure or hyper-converged infrastructure (HCI). Xen and KVM, for example, support multiple cloud platforms, including OpenStack. Nutanix built its Acropolis hypervisor for HCI and scale-out enterprise cloud deployments.
Security and management
When comparing hypervisors, one of the most important considerations is the security mechanisms. Hyper-V, for example, enforces security policies through Active Directory and includes shielded VMs to protect virtual deployments. ESXi, on the other hand, comes with the NSX network virtualization and security platform, which supports microsegmentation and workload-specific security.
IT should also consider VDI hypervisor management. For instance, the Xen hypervisor is part of the open source Xen Project, which provides users with a choice of management tools. IT can compare this to Hyper-V, which only uses Hyper-V Manager, a tool for administering local or remote hosts.
Unfortunately, Hyper-V Manager is suited only for VDI configurations with a small number of hosts. For larger setups, IT teams need management software, such as System Center Virtual Machine Manager, which requires additional licensing fees.
Another important factor is the ability to customize or extend the VDI hypervisor. Xen and KVM are open source hypervisors, so the source code is available to IT to build interfaces or add capabilities. In addition, Citrix now offers XenServer as a free, open source virtualization platform based on the Xen hypervisor.
ESXi is not open source, but VMware still provides APIs to automate VM-related operations, facilitate communication and more.
IT should evaluate a hypervisor's ability to deliver desktops that meet performance requirements. For example, Hyper-V and KVM support disk I/O throttling for controlling disk operations and helping optimize desktop delivery. Organizations should also look to qualified benchmarking data that compares overall hypervisor performance under different workloads.
Desktop availability and reliability are just as important as delivery. When deciding between hypervisors, buyers should account for load balancing, replication, disaster recovery and backup capabilities. For instance, KVM supports VM replication and live migration, as well as hot-plugging, which consists of adding back-end components to bolster virtual resources while the VDI deployment is still running. Xen supports Coarse Grain Lock Stepping, a high-availability software program built on the Remus VM backup technology.
For many IT teams, a hypervisor's scalability is also important. IT should identify metrics, such as the number of nodes a cluster can support, the maximum number of active VMs per node, the total number of VMs and more.
Total cost of ownership
One of the most challenging steps buyers face when comparing hypervisors is calculating an accurate TCO. Although many hypervisors are free, there are other important costs to consider.
For example, organizations must still license the OSes running on the virtual desktops, and they might need to license enterprise-scale management tools. They might also need to purchase equipment or hire more IT personnel to implement and maintain the systems.
In some cases, a free hypervisor might not be adequate for an organization's needs. For example, VMware offers ESXi for free, but IT cannot use vCenter Server to manage the hypervisor or use the vSphere API to back up the deployment. As a result, an organization might need to go with one of the commercial vSphere editions, which include ESXi, vCenter Server and other components.
VMware is not the only product that organizations can turn to when they want a feature-rich VDI hypervisor. For instance, XenServer offers three editions: Enterprise, Standard and Free. The free edition comes with a reduced set of features and is not eligible for Citrix support and maintenance. Hyper-V Server is also free, but it likely requires additional licensing for System Center Virtual Machine Manager or other management software.