Review: Windows Server 2008 R2
Microsoft's initial release of Hyper-V, introduced with Windows Server 2008 in June 2008, was an attractive -- if limited in comparison to VMware -- entrance to the virtualization marketplace. Hyper-V lacked a live migration feature, scalability and some cluster integration features.
Now, with this version, Microsoft is so confident in the robustness of Hyper-V 2.0 that it placed the public Microsoft.com Web site platform on it, serving around 15,000 requests per second, over 40 million hits per day and over 1.2 billion page hits per month.
Arguably the most important inclusion in Hyper-V 2.0 is Live Migration. LM is, of course, Microsoft's response to VMware's popular VMotion technology, which allows you to move a virtual machine from one physical host to another with no down time -- a seamless transition from the perspective of your users. While the existing release of Hyper-V supported quick migration, there were a few seconds of downtime associated with the move; that has been removed. This is great for system maintenance scenarios: If you have a host that needs software updates or hardware maintenance, you can live-migrate VMs from that host to another -- all while keeping user connections and service up -- and then perform whatever changes or fixes are necessary on the now-unloaded host. Then, when done, you can migrate the appropriate VMs back, all without bothering your users.
One unheralded feature of Hyper-V 2.0 is the Cluster Shared Volumes (CSV) feature. Essentially, if you tried to set up a cluster using Hyper-V virtual machines in the original release, for each virtual hard drive (VHD) you had to carve out a LUN on your SAN where that VHD could reside. Since you would likely have 24 or fewer drive letters free, you could end up using Globally Unique Identifiers (GUIDs), those long and clunky alphanumeric identifiers, which could turn into a management disaster.
Enter CSV, which allows you to place multiple VHDs on a single LUN, while the VMs themselves still act as if each VHD is on its own LUN. All CSV volumes are stored in the ClusterStorage root directory, so navigating the different volumes is as easy as clicking through Windows Explorer or navigating directories in the command line.
Hyper-V 2.0 also supports up to 64 logical processors on the host computer and includes the ability to add to a running virtual machine (and remove them) without needing to reboot the OS on that VM. You can also dynamically allocate memory without any interruption of service. Finally, the processor compatibility feature allows live migration across different CPU versions within the same processor family (for example, Intel-to-Intel and AMD-to-AMD), but not across processor families. (VMware has the same limitation.)
Hyper-V 2.0, with all of its improvements, is what some customers have been waiting for before settling on Hyper-V for their virtualization solution. Hyper-V now offers feature parity with VMware's enterprise solutions in some scenarios.