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Last week, I gave you an overview of Microsoft Exchange components—how the Exchange database is designed, the file types it contains, and how it needs to be protected. This week, we'll take a look at common ways to perform the backup and restore of that data. Generally speaking, there are a few standard ways to back up your Exchange systems: offline backups, online backups, and mailbox-level backups.
Offline backups are performed, as you may suspect, by taking the Exchange systems offline and backing up the database and related files to tape as if they were flat files. This is perfectly safe, so long as the databases are put into a consistent state before the backups take place, but it has a few drawbacks. First and foremost, the databases have to be shut down into a consistent state before you take the snapshot. While you can possibly recover from a dataset that hasn't been properly shut down, there is a very high likelihood that you won't get the data back in its entirety.
Secondly, other backup systems can allow you to automatically manage your log file maintenance—the process of removing logs that are committed and therefore no longer needed. Offline backups do not perform that function without additional tools, so they may not be the best option for a time-starved IT staff.
Online backups utilize either the included extensions to Microsoft's NTBackup system, or specialized tools that work with other manufacturers' backup tools. These tools allow the backup systems to dynamically back up the Exchange database and other files while they are being used. Granted, your performance will not be as impressive as it is when the backup isn't running, and the Exchange system may seem less-than-responsive from a client-side perspective, but for the most part, it will continue to function.
Online backups don't eliminate your need for a backup window, but it does minimize that window's impact on your end users. These tools also manage your log files and clean up those that are no longer required to be housed on the servers. This saves you a decent amount of disk space, and eliminates files you no longer need.
Mailbox-level (often called brix- or brick-level backups) are performed by Exchange-specific backup agents or tools, much like online backups. The difference here is that you back up each mailbox as an individual unit that can be restored independently from the rest of the database. This makes restoration incredibly easy if you only need to bring back a single user's files, and can speed up the overall process dramatically.
The main drawback is that this type of backup is generally done at the same time as a database backup, adding to the overall time the process takes. Also, keep in mind that the mailbox-level backup has fallen out of favor with Microsoft, which now recommends using the Recovery Storage Group system in Exchange Server 2003 to merge out a single mailbox when required.
Testing your backup system
Whichever system you use, you will want to perform test restorations at least once a month. If you are using mailbox-level backups, you will want to restore one or two boxes and check to ensure that it's working. Database-level backups (online or offline) will, of course, require restoration of an entire database unit. Both types of testing will require another Exchange server to test with, unless you are using Exchange 2003. In this last case, you can use a Recovery Storage Group to do a test restore, but it is advised even to do this on another server, as you will still have downtime on the production databases during this process. Many large-scale Exchange shops will keep one additional server that can be used for test restores. As a minimum, smaller shops will perform integrity checks on the data on tape using the tape tools that come with the backup systems.
Backing up and testing your Exchange system is mandatory. No other system will allow you to get away with not performing point-in-time backup. While you may be able to do any/all of these types of backup to disk, you need some form of point-in-time copy (disk, tape, or both) in case of a virus attack, malicious employees, or other unexpected file-level corruption that can occur. Now, this is not to say you shouldn't use real-time protection schemes. If you can afford them, they will allow for much faster recovery in many cases. But you cannot eliminate the point-in-time process and hope to properly protect your Exchange data.