I'm currently involved in a project to test Exchange 2000 Enterprise Server on Windows 2000 Datacenter Server. Because Datacenter offers some new capabilities for Win2K and applications, I thought it might be important to spend some time discussing how Datacenter could benefit Exchange 2000.
Datacenter has at least six unique features that aren't available with Win2K Server or Win2K Advanced Server. The first is large memory support: A Datacenter server can address up to 64GB of physical RAM. This is accomplished via an API, which consists of a mere four system calls, called Physical Address Extension (PAE) and is only available on Intel processors later than the Pentium Pro. PAE works by windowing in segments of memory for application use (reminding me of the Lotus Intel Microsoft—LIM—specification of the 1980s). Datacenter also supports up to 32 processors compared to AS's 8-way limit.
Process Control is another Datacenter feature tied to 32-way and large memory support. Process Control is a Microsoft Management Console (MMC)-based tool and command-line utility that gives administrators the ability to finely tune and control resources so that they can assign specific resources on the server to particular applications. Datacenter also supports a feature called hardware partitioning, which lets you run multiple Datacenter copies on the same physical server (e.g., divide a 32-way system into four 8-way servers).
Winsock Direct (also known as InfiniBand), an extension to the Winsock API, is another important Datacenter feature that lets applications take advantage of high-speed networking architectures without needing to understand the underlying transport technology. And last on the list of Datacenter's unique features is four-node Win2K cluster support, which extends support beyond AS's two-node support.
So, how does Exchange 2000 take advantage of these Datacenter features? The answer isn't as exciting as it could be. Unfortunately, design decisions during Exchange 2000's development process prevent it from leveraging all Datacenter's new features. Most notable is Exchange 2000 support for four-node clusters. At Release to Manufacturing (RTM), Exchange 2000 supports only two-node clusters. However, expect Datacenter OEMs to support four-node clusters for Exchange 2000 in the months to come.
Also important is support for large memory configurations. Unfortunately, Exchange 2000's architecture made it difficult for developers to leverage PAE because it would have required major architectural changes that aren't planned until later releases of Exchange Server. For now, Exchange 2000's best use of memory is with servers configured with 4GB of RAM or less leveraging PAE's 4GB Tuning (4GT) feature that has been available since 1997 in Windows NT 4.0 Enterprise Edition.
Processor scalability to 32-way for Exchange 2000 would have been nice, but we'll have to wait until a later release for this functionality as well. Exchange 2000 does scale extremely well to eight CPUs, however. Exchange 2000 deployments should either take more of a "scale-out" approach (i.e., more servers versus bigger servers) or use hardware partitioning because Datacenter supports this feature independent of the application. Partitioning lets you leverage 32-way systems for Exchange deployments.
Process Control and Winsock direct are last on the list, and Exchange 2000 might benefit from them, but little testing data is available to show how much. Process Control might benefit Exchange in the same way that processor affinity tuning has helped some of the high-end MAPI Messaging Benchmark (MMB) benchmarks. Winsock direct might be of greatest benefit for front-end/back-end Exchange 2000 scenarios where message passing between tiers can use the additional bandwidth.
Overall, Exchange 2000 doesn't take advantage of as many Datacenter features as we'd like. Stay tuned, however, because Exchange developers will be working diligently to provide support for more features over time and subsequent releases of Exchange. Official support for Exchange 2000 on Datacenter will be available with Service Pack 1 (SP1), due in First Quarter 2001. After that, either the forthcoming Mercury release or later Exchange versions will fully embrace Datacenter's feature set.