TABLE OF CONTENTS Early Exchange servers used systems built around slow processors, limited memory, and slow disks. The system configuration imposed natural limits for mailbox support, and most deployments did not worry about the 16-GB limit that Microsoft then imposed on a Store database. After all, if you only allocated a 10-MB or 20-MB quota per mailbox, you would not hit the 16-GB limit unless the server had to support thousands of mailboxes, and no server was able to handle the load. There were notable exceptions to the rule especially enterprise customers who scaled using the extra power of the Alpha processor to handle thousands of mailboxes. Enterprise deployments ran into the 16-GB limit and demanded change.
Over time, improvements in hardware and software faster CPUs, better disk controllers, Windows NT 4.0, and especially the vastly superior multithreaded capability of the Exchange 5.5 Store meant that the 16-GB limit became a scalability bottleneck faster than Microsoft could imagine. The initial response was to remove the limit and allow databases to grow to a theoretical 16-TB size in the Exchange 5.5 Enterprise Edition. However, no one could even think about approaching the 16-TB limit, because of storage costs and (more importantly) the issue of how to handle backup and restore operations for huge email databases. Everyone s mailbox was held in a single database, so if it failed, the administrator had to work out how to get the database back online as quickly as possible. With backup rates running at up to 40...
