Microsoft Exchange Server 2003 – Backup Methods


Introduction to Exchange 2003 Backup Methods

Microsoft Exchange server has the usual range of backup methods, full, incremental and differential.  What’s new is Windows Server 2003 supplying the Volume Shadow Copy Service, which speeds up online Exchange 2003 backups.

Topics for Microsoft Exchange 2003 Backup Planning


Volume Shadow Copy Service (VSS)

Windows Server 2003 provides a new Volume Shadow Copy (VSS) service, which produces a mirror of the file system.  The purpose of this VSS* is to allow the operating system to carry on working with the live data, while backup locks onto a shadow copy of the files.

Microsoft even provide a VSS API (Volume Shadow Service Application Program Interface) specifically for backup to hook into these Exchange 2003 databases.  Now here is the strange part, the Windows Server 2003 Backup utility itself, does not make full use of this VSS API; instead it uses the streaming API.  It is claimed that if Windows 2003 Backup did maximise this VSS API, then it would put out of business the companies who have made their reputation on backup software.  See more about Volume Shadow Service.

* Volume Shadow Copy Service uses the VSS API.  Not to be confused with the VSAPI which is the new Exchange 2003 Virus Scanning API.

Types of Exchange Server 2003 Backup

Full Backup
Make it your reflex to make a full backup of Exchange.  Here are two killer reasons why a full backup is so much better than the alternatives; you only need one tape for a restore and a full backup purges the transaction logs.

Only resort to differential or incremental if the time taken by the full backup is unacceptable.  If the duration seems too long for a full backup, try work-arounds like faster tapes, backup to disk then to tape.  Anything to avoid having to use incremental or differential backups.

Differential Backup
If you have tried every trick in the book, and a full backup still takes too much time, then choose a differential rather than incremental backup.  Remember that when you restore differential tapes, there must be a full backup as a reference point.  Traditionally, the full backup is made at weekends, complimented by a differential backup on each weekday night.  Times may vary but the guideline would be the hours of lowest user activity. 

Unfortunately, differential backups do not purge or truncate the transaction logs, so not only does the differential backup get slightly bigger each day, but the logs are using up more and more disk space until you perform the next full backup.

Incremental Backup
Avoid this method.  To prove my point try a test restore on a Friday.  Calculate how many tapes you need and how long it will take.  Realize that there is a five times greater chance of a slip up before the data is recovered, than with a full backup.  Another clue that this is a poor method is that SQL and other relational databases do not allow incremental backups.  Two tiny pieces of good news, incremental backups are quick and they do delete old portions of the transaction logs.

Copy Backup
This is a specialist method which is useful if you need to take a snapshot of the system without altering the archive bit.  Differential and Incremental backups take their cue from the archive property of the files, so my point is that a copy backup doesn’t affect other backup schedules that you have in place.

Daily Backup
This method surprised me, I thought that it would backup any file within the last 24hrs.  Not so.  It only backed up files that had changed since midnight, time stamp 0:00.  I cannot recommend this method for Exchange 2003.

See how to backup outlook with PowerShell »

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Online v Offline Backup

An online backup means that email is not interrupted.  New in Windows 2003 is the Volume Shadow Copy (VSS) service which makes it possible to backup without dismounting the Exchange stores.  Most proprietary programs like Backup Exec, Legato or ArcServe have agents or add-ons which specifically hook into the Windows 2003’s VSS APIs.

Offline backup.  Dismount the Store, then backup.  Not your first choice.  The main reason that I can think of for choosing an offline backup, is if the online backup failed.  The disadvantages are that the logs are not purged and that unlike an online backup, the database cannot be verified.

Another possible scenario is that you are about to undertake risky restore.  So you create a rollback position by backing up what you have already, before you try a restore.

ASR (Automated System Recovery)

I wanted to give you a timely reminder that Exchange 2003 relies on the underling Windows Server 2003 operating system.  In a worst case scenario you will have to rebuild the operating system before you restore the Exchange .edb databases.  An ASR backup and recovery disk is the fastest way of building a base from which you can restore those .edb files.  Before you tackle an ASR recovery, I assume you have tried Last Known Good, Safe Mode and the Recovery Console.

In NT 4.0 days this process was known as RDISK. Both RDISK and ASR suffer from a fatal flaw, that is they are no good unless the disk information is up-to-date.  So, if you going to make ASR diskettes, make sure you repeat the procedure every time the hardware changes in any significant way.

Backup Media Tactics

It is usually fastest to backup to disk.  So, your tactics could be initially backup to disk, followed by a backup to a central server or to a local tape drive.  Perhaps the best strategy would be to employ a tape library on a SAN.

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Summary of Backup Methods in Microsoft Exchange Server 2003

If you want to successfully restore your Exchange 2003 server, then spend time and plan your backup strategy carefully.  Make a full backup your first choice, and wherever possible, avoid incremental backups since they take too long to restore.

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See Also