Configuring Transaction Logs for a Storage Group

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The most important aspect of a storage group is its transaction logs. Even if you use only the default First Storage Group, you must consider your transaction log configuration to make sure that you can recover data if the stores are damaged.

In the standard transaction logging that Exchange uses, each store transaction (such as creating or modifying a message) in a storage group is written to a log file and then to the store. When it is written to the log file, each transaction is labeled with an identifier that Exchange uses to associate the transaction with a particular store. In this manner, all the stores in a storage group share a single set of transaction logs.

This process ensures that records of transactions exist if a store is damaged between backups. In many cases, recovering a damaged store means restoring the store from a backup, replaying any backed-up log files, and then replaying the most recent log files to recover transactions that were made after the last backup.

Note

For detailed information about how transaction logs work and how to recover store data in a variety of circumstances, see Disaster Recovery for Microsoft Exchange 2000 Server. Although existing functionality has not changed, Exchange Server 2003 has new recovery features. For more information about the new recovery features, see What's New in Exchange Server 2003.

When a log file reaches 5 megabytes (MB), it is renamed and a new log file is started. As the number of transactions grows, a set of log files is created. The set continues to grow until you run a full backup (also named a normal backup) or an incremental backup. As part of the backup process, old transaction logs are removed and the current log file becomes the first file of a new log file set. You can control the size of the log file set by using a regular schedule of backups. Using the Windows 2000 backup utility or a third-party backup product, you can back up any storage group or database whenever you prefer.

You can perform four types of online backups on the Exchange store:

  • Full backup   A full backup (named a normal backup in Windows Backup) backs up the store and transaction log files. After the backup, transaction log files in which all transactions are complete are deleted.

  • Copy backup   A copy backup backs up the store and transaction log files, but leaves the transaction logs in place.

  • Incremental backup   An incremental backup backs up the transaction logs and removes all transaction logs in which all transactions are completed.

  • Differential backup   A differential backup backs up the transaction logs, but leaves them in place.

    Important

    You can perform an incremental or differential backup only if you have previously performed a normal backup. If you must recover a store, you must recover the store itself from the last normal backup, and then you can recover log files from an incremental or differential backup.

For detailed steps about how to configure transaction logs and choose other storage group options, see "How to Configure Transaction Logs and Choose Other Storage Group Options"