Microsoft is poised to improve its standing in the world of virtualization with the much-anticipated update to Windows Server 2008 Hyper-V, Redmond's hypervisor-based server virtualization solution for 64-bit Intel- and AMD-based servers. First released last year, Hyper-V proved a less-than-compelling offering compared to virtualization platforms from VMware, Virtual Iron (now Oracle), Citrix, and other rivals. Hyper-V Release 2, part of Windows Server 2008 R2, delivers some exciting new features that change the game.
Among Hyper-V R2's new features is support for 64 logical processors; Live Migration support, which allows admins to move a VM from one physical server to another without service interruption; VM Chimney, which provides TCP offload support; and a new processor compatibility mode for Live Migration, which enables migrations between different CPUs in the same family.
[ See the InfoWorld Test Center review, "VMware vSphere 4: The once and future virtualization king. "]
On top of these enhancements, Hyper-V will remain free with the purchase of Windows Server 2008, which seems like a great deal. However, to use the new Live Migration capability -- and to centrally manage more than one Hyper-V host -- you also need System Center Virtual Machine Manager (SCVMM), which costs $869 per physical server. Depending on what you're running at your organization, SCVMM may be a welcome addition. Among its features, it can manage both Hyper-V and VMware servers.
Start Your Virtualization Engine
Installing Hyper-V is no different than installing standard Windows Server 2008, although you do need to install the new Hyper-V Manager MMC (or SCVMM). The Hyper-V Manager can be installed on the same server as SCVMM or on a separate machine. It can run on Windows Server 2008 or Windows Vista SP1.
Guest operating system images can be installed from physical media or ISO image files, as well as over the network from a network image server. I had no problems installing any of the supported versions of Windows or Linux that I tried.
Installing SCVMM 2008 R2 is somewhat more complex than installing the usual single application: It depends on SQL Server 2005 or SQL Server 2008 (SCVMM will install SQL Server Express, but you'll need the full SQL Server if you'll have more than 150 hosts), plus PowerShell 1.0, the Windows Automated Installation Kit 1.1, IIS 7.0, and an instance of System Center Operations Manager 2007 for reporting. Installing Operations Manager isn't strictly necessary, but only through the combination of SCVMM and Operations Manager can you monitor and manage virtual servers and their physical hosts together.
Worth the Hype
Hyper-V's spiffy new features worked well; at least, those I was able to try did, which included Live Migration and processor-compatibility mode. My lab was not equipped to test 64-core support, and TCP offload requires a new NIC from Intel or Broadcom. Live Migration is not simple to implement, as it requires adding several roles to each Hyper-V server as well as using SCVMM, but the steps are not onerous and I had no trouble getting everything to work.
Live Migration is far superior to the Quick Migration feature in the previous version of Hyper-V. Using Quick Migration, it generally takes 30 seconds or longer to move a VM from one physical server to another, long enough that most client applications lose their connection to the server and experience some kind of failure. Live Migration moves a VM without any service interruption; even heavily loaded servers can be moved without problems. I saw short delays (one to two seconds) when migrating a VM with 4GB of memory while running load simulation tools, but the server was always reachable and the delay wasn't long enough to cause the application to fail. With smaller VMs (1GB and 2GB of memory) delays were not perceptible.
Hyper-V R2 also includes Cluster Shared Volumes, a new feature that allows two physical servers and multiple VMs to share the same volume or LUN. This not only makes setting up storage much easier, but it's necessary for VMs that may need to migrate from one physical server to another. Cluster Shared Volumes is the storage foundation that makes Live Migration possible.
The processor-compatibility mode for Live Migration eases the task of setting up backup servers or secondary servers for higher loads by negating the requirement that the physical servers have the same model CPU. Rather, the CPUs need only be from the same family, thus opening the opportunity to use older servers with earlier-model CPUs for backups. For instance, I was able to migrate VMs from an HP ML370 G5 with dual Xeon 5400 CPUs to an HP DL360 G4 with dual P4 Xeon 3.6GHz processors.
Enable with Caution
Processor compatibility mode doesn't eliminate all CPU-related obstacles. For starters, migrations between AMD and Intel servers remain impossible (to be fair, no virtualization platform has overcome this hurdle yet). Further, the CPUs require support for either Intel Virtualization Technology or AMD Virtualization, which means you're limited to relatively recent CPU models. You won't be able to use those old Pentium Pro servers. Bear in mind that processor compatibility mode is turned off by default, as it can reduce the functionality of that nice, new processor to its base. In short, you don't want to enable processor compatibility mode if you're not concerned with migration.