The Exchange Message Store

Exchange Server 2003 supports the use of two types of stores: mailbox stores and public folder stores. Each store is a logical database that includes two database files. The first file is the streaming database file (.stm) which stores Internet-formatted messages, such as native Multipurpose Internet Mail Extensions (MIME) content. Any messages in Internet format that are submitted to the store by any client, other than MAPI clients, are stored in this file. The second file is the MAPI database file (.edb), which contains all messages submitted to the store through MAPI, as well as the database tables that define mailboxes, messages, folders, and attachments. Properties of Internet-formatted messages are promoted to the MAPI database so that the messages are listed in the Inbox of MAPI-based clients. In other words, the .stm file contains the content of e-mail messages in Internet format, such as UUENCODE or MIME, which is referenced by the corresponding .edb file. This means that the streaming database and MAPI database files that comprise a particular database cannot be separated.

Exchange Server 2003 Database Technology

Exchange uses Extensible Storage Engine (ESE) to maintain transaction-based databases, and uses write-ahead transaction log files to ensure that Exchange data is efficiently processed. The transaction-oriented Exchange store provides for maximum recoverability. A transaction can include multiple actions, but for the transaction to be committed, all actions must complete successfully. If one part of the transaction cannot be completed, the entire transaction is rolled back and not committed to the database. For more information about transaction handling in Exchange Server 2003, see Exchange Information Store Service Architecture.

Stores and Storage Groups

You can split the Exchange store into multiple storage groups and stores. A storage group is a group of databases that share a single transaction log. A store is a single database than contains the mailbox or public folder contents. In Exchange Server 2003, you can configure up to four storage groups on each server running Exchange Server. Each storage group can contain up to five stores. Exchange Server 2003 also includes an additional, dedicated Recovery Storage Group. The Recovery Storage Group can be used to restore mailboxes or stores while the other stores remain online. For more information about storage groups and the Recovery Storage Group, see Exchange Information Store Service Architecture.

The following figure shows one possible storage group and store configuration on a server running Exchange Server.

Stores and storage groups on a server running Exchange Server

The primary reason for deploying multiple storage groups and stores is to reduce the size of each individual database while still supporting many users on one server. Having multiple smaller stores enhances Exchange Server backup and recovery. Because all of the stores in a storage group share a transaction log, each storage group should be backed up as a whole. If your backup infrastructure supports multiple backup streams, you can back up multiple storage groups at the same time. If you must restore data on the server running Exchange Server, you restore each store individually. When you restore each store, you can mount it and make it available to users.