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Overview of Exchange Server Backup Methods


Letztes Änderungsdatum des Themas: 2006-09-06

By Nino Bilic

Several backup methods are written that do not use the Microsoft backup API. The following is an overview of backup methods that you can use.

This article divides backups into two categories: what Microsoft supports and does not directly support.

The following are the Microsoft® Exchange backups that Microsoft supports:

  • Online backups
  • Offline backups

Online backups are backups done while Exchange services are running. None of the Exchange services have to be stopped for this backup to complete.

Online backup does not mean that you try to back up Exchange database files and Exchange folder structure while Exchange services are running. Online backup means backing up a separate Microsoft Exchange or Microsoft Exchange Server object that is available in backup software. You can do an online backup using Backup if you install Exchange administrator or Exchange System Manager in Exchange 2000 Server on a server that will do a backup. If you use third-party backup software, you have to install the Exchange Agent or Exchange-aware backup software. Agents are popular because they extend the functionality of third-party backup software. You will be backing up Exchange Directory (Exchange Server version 5.5) or Microsoft Exchange Information Store service objects. You will not be able to select individual files to back up or select individual mailboxes that need to be backed up.

If you try to back up actual Exchange Server files and folders while services are running, backup will complete but with files that are skipped. Database files are skipped because the Exchange database engine has opened them, and only one program can have exclusive access to a single file on the disk. If disaster strikes and this is the only type of backup available, it is possible that Exchange information will not be recoverable.

When backing up Exchange Server databases, there are four backup types available:

  • Normal (or Full)   The normal backup process backs up the directory or Exchange store in its entirety, as well as the log files. To restore from a normal backup, only one normal backup is needed. A normal backup marks the objects it has backed up so that incremental and differential backups have context. This is accomplished by backing up the entire database and all the log files, and then purging the log files.
  • Copy   The copy backup is the same as a normal backup except no marking takes place to give incremental and differential context. This means that performing an incremental backup after a copy backup is equivalent to performing it before a copy backup. Use a copy backup to get a full backup of the directory or Exchange store without disturbing the state of ongoing incremental or differential backups.
  • Incremental   An incremental backup backs up the subset of the component that has changed since the last normal or incremental backup. Then it marks these objects as backed up. To restore from incremental backups, each incremental backup since the last normal backup and the normal backup are needed. An incremental backup backs up only the log files, and then purges them.
  • Differential   A differential backup backs up changes in the directory or Exchange store that have occurred since the last normal backup. To restore from differential backups, one differential backup and one normal backup is required. A differential backup backs up only the log files but does not purge them.
    In few cases, performing a differential or incremental backup is disabled, for example, immediately after an offline defragmentation or while circular logging is enabled.

To restore an online backup in Exchange 2000 Server, you need the Microsoft Exchange Information Store service running, and the stores that are being restored need to be dismounted. To restore an online backup in Exchange Server 5.5, you need to have the Microsoft Exchange System Attendant service running.

Offline backups are backups of Exchange files and folders when Exchange services are not running. If services are not running, backup software can have exclusive access to database files and can back them up.

Planned offline backups will result in consistent database files. When Exchange services are being gracefully shut down, all transactions are being committed to the database. Resulting databases will be consistent, marked consistent or clean shutdown, depending on what version of Exchange you are running.

Unplanned offline backups are backups that are taken when the server fails. Database files are copied to some location because that is the only type of backup available. If Exchange Server fails before this backup, databases do not have to be consistent, so they might need repair after the restore procedure. Make sure to check if the backup was before or after the failure or Exchange Server problem.

For backup methods that are not supported, there is no guarantee that the methods will work. You should contact your third-party backup software or hardware vendor in case of problems with backup. The backup vendor should be the primary source of support in the case that any of the following backups are used. Microsoft will work with any customer that has any backup type. However, if the backup was created by one of the following methods, the only help that Microsoft might be able to provide is disaster recovery, which might involve data loss.

There are third-party backup programs that use special ways to do a file-level backup of files that are already opened by some other application, such as Exchange Server. This might or might not work. In most cases, it will not work for Exchange. There is no guarantee that this type of backup will back up all mailbox and public folder data, and that you will be able to recover from disasters such as this. Open file agent backups, in most cases, back up inconsistent databases.

There are several third-party backup programs that can back up and restore individual mailboxes, rather than whole databases. Because those backup solutions do not follow Microsoft backup guidelines and technology, they are not directly supported.

There are known problems with some versions of mailbox-level backup programs including loss of free/busy data and incomplete restores. Every effort is made to help, and to look at the errors and issues that you are having with this type of backup and restore, to determine if there are Exchange problems documented that could cause this error.

This type backup provides benefits somewhat in between offline and open file agent backups. These backups are typically done on a hard disk instead of tape devices, which allows much faster transfer rates.

Traditionally, the snapshot backup is done when databases are stopped. Because they are consistent, the restore procedure is similar to offline restore procedures. Those types of snapshot backups require downtime when backing up.

There are some backups that perform what is called a Hot Split backup. This can be thought of as a snapshot backup with an open file agent running. The result is a fast backup that does not require downtime, but the backed up databases are inconsistent. Because of that, the backup vendor might need to be contacted to make sure that data is restored without any loss.

A server running Microsoft Windows Server™ 2003 will support snapshot backups, and they are supported in Exchange Server 2003. They will utilize the Volume Snapshot service of Windows Server 2003, and they will require both the Exchange snapshot DLL and the special storage hardware.

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