Administrators like anything that helps reduce cost and complexity while assuring users high-quality service. If you've been running Microsoft Exchange Server for a few years, though, you know that Exchange server consolidation hasn't always fit that bill. Although benchmarks show that today's hardware can comfortably cope with many thousands of mailboxes, you might refuse to host more than 2000 or 3000 per server because of concerns about backup and disaster-recovery times. Or perhaps slow network links have forced you to place servers in remote offices.
Exchange 2000 Server delivers features such as clustering, store partitioning, and increased reliability that make the product increasingly viable on fewer servers. When you correctly deploy and manage Exchange clusters, they certainly help overall system availability. However, memory-fragmentation problems in the Exchange 2000 Store process have made clustering less popular than it might be. Store partitioning can keep databases to a manageable size, but storage group (SG) design is still an evolving science—finding a definitive figure of the optimum number of databases and SGs to use with high end servers is nearly impossible. And although Exchange 2000 is certainly more reliable than earlier versions, its additional feature set also makes management more complex. Exchange Server 2003 improves on several of these factors.
Exchange 2003 (Enterprise Edition) supports four-node and eight-node clusters on Windows Server 2003 and Windows 2003, Enterprise Edition, respectively, compared with Exchange 2000's support for two-node and four-node clusters on Windows 2000 Server and Win2K Datacenter Server. Until now, most companies have deployed Exchange on standard servers, so clustering has appealed to a limited market. The availability of eight-node clusters is unlikely to create a run on clustering, but the availability of four-node clusters on a much less expensive standard server might make system designers reconsider clusters for Exchange. Although you can run eight-node clusters on Windows 2003, Enterprise Edition, I think such implementations will be the exception rather than the norm, at least for the next few years.
Servers that support more mailboxes usually have larger databases. A 250GB private store poses a management challenge of quite a larger proportion than does a 50GB store. Hardware capabilities aren't the problem, but the time necessary to perform regular online backups and restores of such a large database might be. If restoring a database on your server takes longer than 8 hours, you probably don't want to support more mailboxes on that server, regardless of whether it could support them. Although storage vendors such as EMC and Hewlett-Packard (HP) offer fast backup solutions, such products have never been fully compatible with the Store, largely because Microsoft never built the necessary support into Exchange. Windows 2003's Volume Shadow Copy Service (VSS), however, opens new possibilities for how the OS can work with applications such as Exchange and with storage and backup vendors to create hot snapshots and clones. I expect this new technology to help servers support much larger databases, but first you must have a full set of VSS-compliant storage and backup software products.
Microsoft has also enhanced Microsoft Office Outlook 2003 in an effort to reduce the network and server load that clients generate. The idea is to better use existing network links so that Exchange can support more clients across those links. In theory, these enhancements will mean that you can consolidate servers more easily—as long as users don't generate enough additional workload to offset the advantages of an Exchange 2003–and–Outlook 2003 combination.