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.
Also for performance reasons, VM Chimney and Virtual Machine Queue are both disabled by default. VM Chimney allows TCP/IP to be offloaded to a physical NIC, which reduces CPU loads substantially. However, it's not compatible with every NIC. Also, it's not suited for all types of traffic. You may not see improvement among applications with small packets and interactive traffic, though SQL traffic, backups, Live Migration, and other applications that make use of larger packets and streaming traffic will benefit greatly.
Windows Server 2008 Hyper-V R2 and System Center Virtual Machine Manager 2008 R2
|Pros||Support for up to 64 cores in Hyper-V. Live Migration allows failover (due to unresponsive server or agent or threshold-based automation) from one physical server to another without interrupting client access. Cluster Shared Volumes makes setting up storage for failover much easier. SCVMM can manage both Hyper-V and VMware servers.|
|Cons||P2V and V2V migration is one direction only; you can’t migrate VMs from a Hyper-V server to a VMware server.|
|Cost||Live Migration and other advanced Hyper-V features are available only in Windows Server 2008 R2 Enterprise and Datacenter editions, and in the free stand-alone Hyper-V Server 2008 R2. Windows Server 2008 R2 Enterprise starts at $3,999 with 25 CALs; Datacenter edition starts at $2,999 with no CALs. System Center Virtual Machine Manager 2008 R2 license costs $869 per managed physical server.|
|Platforms||Hyper-V requires a 64-bit Intel- or AMD-based server that supports hardware-assisted virtualization (Intel VT or AMD-V) technology, and it supports Windows Server 2008, Windows Server 2003, Windows 2000 Server, Windows Vista, Windows XP, Suse Linux Enterprise Server, and Red Hat Enterprise Linux guests. System Center Virtual Machine Manager 2008 R2 requires a Windows Server 2008 host and a SQL Server 2005 or SQL Server 2008 database.|
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