In this short review we're going to make comparison between such software hypervisors as Hyper-V developed by Microsoft, ESXi created by VMware and XenServer from Citrix. Of course, there are other hypervisors, but these three are the biggest players in the current server virtualization market.
ESX(i) is a component of a VMware vSphere which offers many advanced features for management and administration, such as vMotion (live migration), High Availability, Fault Tolerance, Storage Motion. VMware has a powerful infrastructure because of multiple third-party vendors developing wide variety of tools. However, it is very pricey, compared to other server virtualization platforms. Though it is worth investing and according to statistics 76% of organizations choose VMware hypervisor. It is targeted mostly at the large enterprises.
Hyper-V is the server virtualization platform developed by Microsoft. It is mostly used by the SMB companies. It has such features as Live Migration, Quick Migration, and Dynamic Memory. Microsoft offers its hypervisor in two versions: stand-alone software and a component included in the Windows Server 2008 OS.
Hyper-V is free but you should buy Windows Server that costs. Moreover, you can purchase Microsoft System Center software suite and System Center Virtual Machine Manager for management of Hyper-V and VMware environments, but for this you need to pay additional money. According to the survey, Microsoft Hyper-V controls 13% of the server virtualization segment in IT industry.
Usually, Hyper-V is selected as a hypervisor by the users who don't have exceptional performance and functionality requirements. This virtualization tool supports limited number of applications and utilities.
Xen is not as user-friendly as Windows-based hypervisors. Because it is based on Linux, while the most widely-used operating system is Microsoft Windows, this hypervisor isn't as popular as Hyper-V or VMware hypervisors. But if your organization already uses Citrix products, you should think of Xen because you already have expertise with this vendor. The market share of Citrix XenServer is about 3%.
Xen proved to be a stable product, but it doesn't have as many Enterprise features as Hyper-V or ESXi do. XenServer can be managed through the command line interface (CLI). To help administrators used to the other hypervisors, there is a GUI management client - XenClient - that allows easy management of the Xen virtual infrastructure.
Choice of a hypervisor very much depends on your requirements. If you need a simple virtualization platform then you could just get a free version of Hyper-V or ESXi. These two are the most popular hypervisor platforms that have really professional support and are constantly extended by the new features. XenServer also has its advantages for those experienced in the Linux operating system.