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How Microsoft Exchange Server Organization Hierarchy Works

A Microsoft Exchange Server messaging system comprises several administrative units, the largest of which is the organization. The organization hierarchy varies depending on the version of Exchange Server you are using:

• Exchange Server 2003--In Exchange Server 2003, the organization hierarchy includes organizations, administrative groups, servers, and storage groups. The organization is the highest level in the hierarchy and includes the entire enterprise. An administrative group is a set of servers that share an administrative security context. Each server in the administrative group can have up to four storage groups. Each storage group includes up to five database stores that can be mounted and dismounted independently. For more information on the Exchange Server 2003 organization hierarchy, see your Microsoft Exchange Server documentation.

  Note: If you are using Exchange Server 2003 and want information on performing Volume Shadow Copy Service backups, see the Microsoft Volume Shadow Copy Service Guide.

• Exchange Server 2007--In Exchange Server 2007, there are four organization models:
  • Simple Exchange organization
  • Standard Exchange organization
  • Large Exchange organization
  • Complex Exchange organization

  Note: For more information about Exchange Server 2007 organization models, see the Microsoft TechNet web site.

  Each Exchange mailbox server in the organization can have up to 50 storage groups. In a non-replicated environment, each storage group can have up to five database stores. In a replicated environment, each storage group can have one database. Each database can be mounted and dismounted independently.

• Exchange Server 2010--In Exchange 2010, storage groups are no longer supported. A Database Availability Group (DAG) is a collection of up to 16 mailbox servers, where each server stores up to 100 mailbox databases. A copy of a database can be stored on any server in a DAG. Some additional changes in this version:
  • Recovery Storage Groups have been replaced with Recovery Database
  • Database names must now be unique across your organization
  • All copies are located at the same paths
  • Active Manager is required to mount a database and determines which database is mounted
  • All high availability configuration is performed post-setup
  • Exchange Server 2010 server roles are supported by Windows Server 2008 with SP2 or later and Windows Server 2008 R2.
  • Exchange Server 2010 and prior versions can be installed in the same organization.

  The concept of a Database Availability Group provides failover at database level, rather than server level, and is transparent to end users. In a DAG, only one copy of a database is active at any one time. CA ARCserve Backup lets you choose to back up from active databases or replicas. DAGs can include mailbox servers in separate physical locations, as well.

  In this example, five members comprise the DAG with a sixth one off-site. Databases are spread across the DAG so that no two members have the same database configuration. This configuration is Microsoft's suggestion for providing database availability in the event of hardware failure. Users access the Exchange Server and are routed to the active database. Supose DB1 hosted on Mailbox Server 1 is active. If Mailbox Server 1 fails, users can be routed to the copy of DB1 on Mailbox Server 2. If Mailbox Server 2 fails, users are routed to the copy of DB1 on Mailbox Server 4. For more information on how DAGs work, see the Microsoft website.