Performing an Exchange Server 2003 backup

Performing an Exchange Server 2003 backup

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There are two types of data that need to be backed up: static and dynamic. The static data seldom or never changes. This data can be a Windows Server 2003 operating system along with service packs, packaged application software, third-party backup utilities, user application software, or management scripts. On the other hand, the dynamic data changes frequently. It can be Exchange Server 2003 database and log files, Active Directory data, Site Replication Service databases, cluster quorum, etc. Exchange Server 2003 uses database files and transaction log files to store user data. Each database file consists of two files: the rich text file and the streaming file. Both are managed by the Microsoft Exchange Information Store service. Exchange Server 2003 uses the transaction log files to record day-to-day transactions. These files are the primary storage areas for new transactions. They contain all Exchange data and are required to be backed up at regular intervals. When a user creates a new message, it is not written directly to an Exchange database file. Instead, it is written to a log file before being finally written to the database file.

Administrators can perform a backup by using the Windows Server 2003 backup utility. They can choose different backup strategies depending upon the requirements and situation. They can choose the full backup, copy backup, incremental backup, or differential backup. A full backup copies the database files and the transaction log files. When a full backup finishes, all the transaction log files that have been committed to the database are deleted from the server.

As Exchange Server 2003 database could be very large, and a full backup copies both the database and transaction log files, it is improper to take a full backup every day. However, after completion of the full backup, the transaction log files are deleted from the server. As a result, it takes longer to complete. Therefore, it is not recommended to take a full backup on a regular basis. Instead, administrators should use another method called the incremental backup for taking daily backups.

An incremental backup does not back up database files. It backs up only those transaction log files that were not backed up earlier. However, before taking an incremental backup, circular logging must be disabled on the server. Another method called the differential backup does not distinguish between backed-up and non-backed up transaction log data. It just backs up all transaction log files each time. The copy backup is similar to a full backup, except that no file marking is performed after the backup. This backup method is generally used to create archived data that can be stored off-site.

Although any of the backup methods can be used to back up the Exchange Server 2003 databases, an administrator should choose a method according to the requirements and after considering the amount of data to be backed up. As an incremental backup takes the backup of only the uncommitted transaction logs, it completes in less time. Therefore, it is the most recommended method for taking daily backups. However, administrators should take a full backup periodically in order to control the size of the Exchange transaction log files, which a full back up deletes after the backup completes.

An administrator can perform the backup either online or offline. During an online backup of Exchange Server 2003 databases, all services, including Exchange stores, run normally throughout the backup process, and users can use their mailboxes without any interruption. During an offline backup, the .edb, .stm, and .log files that comprise the Exchange store are backed up and checked for corruption. This check verifies the checksums on each 4KB block or page in the database. In the event of a checksum failure, the backup aborts. Therefore, when an online backup completes, the administrator should always check the Event Viewer to ensure the integrity of the Exchange store that has been backed up.

Contrary to an online backup, the mailbox and public folder stores must be dismounted before performing an offline backup of Exchange databases. In an offline backup, the transaction log files containing transactions committed to the database are not purged, and databases are not checked for corruption. It increases the chances of data loss. Therefore, the offline backup method is not recommended. It needs to be performed only if an online backup fails.

Volume Shadow Copy Service (VSS) : It is an efficient backup method, which can reduce the time consumed in taking a backup. It is a Windows Server 2003 service that enables a backup software or utility to create a shadow or snapshot of Exchange Server 2003 databases at a specific point in time, and take a backup from that shadow copy. Using the VSS service, backup software can take an instantaneous backup of Exchange Server 2003 data. Exchange Server 2003 supports VSS for full and copy backups only. An incremental or differential backup cannot use the VSS service.

After performing a backup, an administrator needs to verify whether or not it has been performed successfully. To accomplish this, he needs to examine the Windows Server 2003 event log. By examining the event log, he can be sure that the backup was completed successfully and as scheduled.

Therefore, performing backup and restore operations is a very critical task performed by an administrator. In order to successfully take the backup of Exchange databases, he should carefully choose from among the available backup strategies.

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