Past options for backing up Microsoft Exchange Server were to perform either an online backup or an offline backup. Other technologies, such as continuous data protection and continuous
replication, have been added to the mix. While there are several different ways to back up Exchange Server; no single method is perfect. In many cases, the best approach is to use a combination of different backup strategies. This tip explains various available backup methods for Exchange Server, and the pros and cons of each.
Online Exchange Server backups
Online backups have been the preferred way to back up Exchange Server, with the primary advantage being that it's a mature and stable backup method. The downside is that your backup software must be Exchange Server-aware. When you install Exchange Server, the Setup program modifies NTBACKUP to become Exchange-aware. If you're using a third-party backup application, you must purchase an extension for Exchange Server. This tends to be expensive.
The biggest con to online backups is the potential for data loss. For example, if you perform your backups daily at 11:00 p.m., what happens if a catastrophic database failure occurs at 4:00 p.m.? You could restore the backup from the night before, but unless transaction logs are still intact, you'll be missing any data that was written to the server since the last backup.
Traditional backups are also very slow. Many organizations are trying to back up a data set that grows exponentially within a finite backup window. In many cases, the backup window isn't expansible, because the backup process consumes network resources that must be available when users first sign on.
Offline Exchange Server backups
In my opinion, offline backups are the most reliable; however, they're not practical for day-to-day use. With offline backups, the Exchange Server database is offline while backups take place. This means that the database is in a known state.
Offline Exchange Server backups are perfect if you're migrating to a different server, because no additional messages can be sent or received until the database is brought back online. Additionally, your backup software doesn't need to be Exchange-aware, because the backup is occurring at the file level.
The downside to this type of backup is that you have to take the database offline, making it completely inaccessible to users until you bring it back online.
Continuous data protection
One of the newer types of backups that can be used for Exchange Server is continuous data protection. The concept behind continuous data protection is that small backups are made throughout the day, rather than running a single monolithic backup at night. This greatly reduces the amount of data that would be lost if a catastrophic failure occurred since backups happen frequently.
For example, Microsoft's Data Protection Manager (DPM) can create backups as often as once every 15 minutes. Because small backups are made so frequently, the need for a dedicated backup window is usually eliminated.
Typically, continuous data protection solutions first make volume shadow copies of the Exchange server. After that, periodic backups typically copy transaction logs to the server, although occasional full backups can be scheduled. There are several different continuous data protection solutions available for Exchange, and they all work a little bit differently.
Continuous data protection is expensive, though. Typically, you need a dedicated server to act as a backup server. Since continuous data protection uses hard disks as its primary backup media, the server will either need a lot of available disk space -- usually in the form of a high-performance array -- or be connected to a storage area network (SAN).
You also must consider the cost of the software license. Additionally, it's important to back up the continuous data protection server to tape regularly. Therefore, you'll need a tape drive and possibly some traditional backup software.
Similar to continuous data protection, continuous replication uses log shipping to copy log files to an alternate location for safekeeping. One benefit of this method is that log files are shipped as soon as they are filled up, which means that backups can occur even more frequently than they would with continuous data protection.
Continuous replication is native to Exchange, so there's no additional software to purchase. You can configure continuous replication to copy your transaction logs to another volume on the mailbox server (local continuous replication) or to copy the log files to another Exchange server (cluster continuous replication and standby continuous replication).
Keep in mind: This type of replication solution isn't appropriate as your only form of backup. While it will protect you against a hard drive failure, it won't protect against corruption. A corrupt log file would be copied to the backup destination.
Continuous replication augments a traditional backup, since you can run your backups against a copy of the database, rather than backing up the primary database. This means that you can run a backup without affecting your Exchange server's performance.
This type of backup has some disadvantages, though. Unlike other backup strategies, continuous replication only works with Exchange Server 2007. Additionally, as a standalone solution, it doesn't offer the ability to restore a database to a previous state or granularly restore individual mailboxes.
About the author: Brien M. Posey, MCSE, is a five-time recipient of Microsoft's Most Valuable Professional award for his work with Exchange Server, Windows Server, Internet Information Server (IIS), and File Systems and Storage. Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal website at www.brienposey.com.
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This was first published in August 2008