Storage group

A collection of Exchange databases on a server running Exchange 2000 that share the same Extensible Storage Engine (ESE) instance and transaction log. Individual databases within a storage group can be mounted and dismounted. Each server running Exchange 2000 can architecturally host up to 16 storage groups, although only four can be defined through the Exchange System Manager. [Exchange 2000]

A collection of mailbox stores and public folder stores that share a set of transaction log files. Exchange manages each storage group with a separate server process. [Exchange 2003]