Product review: Windows Server 2008 is the host with the most, and the perfect guest
Microsoft's slimmer and stronger server OS, bolstered by virtualization, networking, and security advances, is an upgrade that IT can't refuse, a 200-pound gorilla that eats commercial Linux
Relaxed licensing is a huge win for shops that deploy Windows Server 2008. Buy a big, fat, fast x64 server, and you can use one Windows Server license to host as many virtual guest instances as you like on that one server. Each physical server requires its own license, and Microsoft seat licenses still apply across the board, but I can see an eight-socket Opteron server easily pulling the workload of a half rack of very busy two-socket rack servers, or a full rack of similar servers with typical utilization.
Of course, Microsoft virtualization works on Intel Xeon as well, albeit with lower single-server consolidation capacity. (Lest anyone think I'm harping, I'll write about the enormous advantages that Opteron brings to Windows Server 2008 virtualization elsewhere.) Hyper-V leverages AMD and Intel hardware-accelerated virtualization to reduce the overhead of software virtualization to a minimum. I say "reduce" to cover edge cases, but for most uses, Hyper-V makes the overhead of trapping privileged instructions and swapping guest OS instance contexts in software disappear. Plus, Hyper-V is very flexible in its resource allocation, permitting guest instances the privilege of "owning" a peripheral. When you can afford this, the layers devoted to arbitrating access to a single device by multiple virtual guests are bypassed. I/O bandwidth for each virtual machine can approach native performance. This feature favors servers with lots of expansion slots. For existing servers, you can buy a PCI-Express bus extension chassis to create a bank of, say, LAN adapters to give each virtual instance its own card.
Devoting devices to guests takes away the I/O bottleneck, but it also aids availability through redundancy. A dead LAN card or host bus adapter, or a downed route, won't be felt by users or applications as long as you've done the network and peripheral redundancy you'd build into any enterprise plan. However, you may opt to skip some of that homework because all but catastrophic contingencies short of a whole server going up in smoke are adequately covered by Hyper-V. Continuity and load distribution architecture and management are addressed by Hyper-V's snapshot, guest instance migration, and direct access to virtual disk images for offline virtual machines.
A whole new level of manageability is enabled by what I consider to be an essential add-on to Windows Server 2008. Microsoft's System Center Virtual Machine Manager adds intelligent monitoring, provisioning, and placement of virtual machine images and workloads across your network. System Center Virtual Machine Manager is fantastic once you make the effort to wrap your mind around its concepts and the shortcomings in its user interface. I lived in System Center Virtual Machine Manager's Workgroup Edition during my testing, a $499 package that runs up to five physical servers, and I can't imagine being without it. The full System Center suite, which is scaled and licensed for enterprise use, includes Virtual Machine Manager.
Big services for small clients
Windows Server 2008 covers another flavor of virtualization in the form of Terminal Services. A mainstay of Windows Server, the big news in this release is its HTTPS tunnel, or Terminal Services Gateway. Edge security often blocks inbound access to the TCP ports needed by Terminal Services. The Terminal Services Gateway allows remote clients normally blocked by firewalls to access Terminal Services, without the hassle of VPN, but with full security and auditing.