Microsoft's Hyper-V R2 is hot on VMware's heels
The much-improved Hyper-V R2 and System Center Virtual Machine Manager 2008 R2 combo smooths the bumps to Windows server virtualization
Virtual Machine Queue allows a NIC to use DMA (Direct Memory Access) to route network traffic directly into a VM's memory, which eliminates both packet copies in the virtual network and route lookups in the virtual switch, thus improving performance significantly. Currently, only a few Intel and Broadcom NICs support VMQ.
Robust management not included
The Hyper-V Manager plug-in for the ubiquitous Microsoft Management Console (MMC) is perfectly adequate for monitoring and managing a few Hyper-V servers. It can be used to manage any Hyper-V feature, including Quick Migrations and Live Migrations. But for more sophisticated management of larger environments, you'll need SCVMM.
SCVMM offers substantial benefits for the price. In addition to allowing both manual and automatic Live Migration, it supports physical-to-virtual and virtual-to-virtual migration from VMware hosts to Hyper-V hosts. Further, it allows the same management of ESX hosts that you get through VMware vCenter (because it works through vCenter), enabling management of a mixed Hyper-V and ESX environment from one console. Moreover, SCVMM supports libraries of VM templates, hardware profiles, and ISO images to simplify the deployment of multiple VMs.
SCVMM also provides a fault tolerance feature similar to VMware's High Availability. You can monitor a server, and if that server stops responding, the VM will automatically restart on another server. Configuring this is not quite as simple as a drop-down menu selection; you need to script it, but it isn't difficult and certainly doesn't require research to figure out.
Finally, SCVMM also includes some nice monitoring and reporting tools. It can send e-mail notifications if utilization exceeds a given threshold, for example, and it provide reports that show that the Hyper-V server is earning its keep, and that help identify potential bottlenecks before they become problems. Performance and Resource Optimization (PRO) -- a new SCVMM tool that requires Operations Manager -- is useful for optimizing and troubleshooting a Hyper-V server. It provides application-aware advice on getting a Hyper-V server to run better. The advice can be basic, but it can produce useful information on making specific applications, such as SQL Server 2005, run in a VM.
Hyper-V vs. VMware
Given all the improvements Microsoft has poured into Hyper-V, one might wonder how it stands up to the offerings from the reigning virtualization champ, VMware. Though Hyper-V has made some dramatic strides, it needs to put on more muscle before it can go toe-to-toe with VMware vSphere 4 (or its predecessor, VMware Infrastructure 3).