Traditional backup software is no match for Exchange.
For many years, traditional backup products have tried to address the challenges that come with protecting and recovering e-mail messages. The advent of Microsoft[R] Exchange 2000 and 2003 brought new increases in Message Store size and a scalability challenge for many organizations. Traditional tape backup methods are simply not capable of keeping up the increased size of Message Stores and the limited backup window. Adding new challenges are recent regulations that require organizations to archive e-mail. Traditionally, companies have turned to traditional backup methods for protect Exchange.
For the majority of organizations, tape backup is the preferred solution to protect Exchange. You have the option of using the free backup utility, NTBACKUP.EXE, provided by Microsoft or you can use one of the popular 3rd-party backup products. These tape backup products perform online backup of Exchange and stream data from the Exchange database to tape media at high speeds. Using the Exchange Backup API (ESE--Extensible Storage Engine), these 3rd-party products perform a full backup of Exchange including all databases and log files.
Normal practice is to perform a weekly full Exchange backup. Each day an incremental Exchange backup is performed to copy new log files. After completion the log files are truncated. Optionally a differential backup makes a copy of the new log files since the last full backup, but does not truncate the logs. In the event of a recovery, the full backup tape is restored followed by the incremental backup tapes. Recovery time increases with the number of tapes to restore, so many users prefer a daily full backup of Exchange if their backup window permits.
The traditional tape backup methods allow for a full recovery of the Exchange database(s). In the event of a hardware failure or corrupt database, the entire Exchange database can be restored from tape. The recovery time is dependent on the amount of data contained in the Exchange database. As a general rule of thumb, the recovery time is two to three times the amount of time it takes to perform the backup. For a typical 40 GB Exchange database, the backup time is 1-2 hours and the recovery time is 2-6 hours, depending on the amount of log files.
For most organizations, going without e-mail service for more than 2 hours is unacceptable. One alternative is to use a Recovery Server. A Recovery Server is a complete Exchange Server running in standby, ready to take over e-mail services when the primary Exchange Server fails. New in Exchange 2003 is a Recovery Storage Group. A Recovery Storage Group is a storage group that is available to take over temporary e-mail services when a primary storage group fails.
[FIGURE 1 OMITTED]
It is essential that you protect Exchange from a total system failure and are able to restore a complete Exchange database. However, the most common errors that impact Exchange are not system hardware failures, but human errors. One common system administrator error is to delete a user mailbox. If a large number of mailboxes are active it is easy to confuse mailboxes and delete one by mistake. The Exchange Backup API supports full Exchange database backup only and does not support mailbox restore; therefore, some interesting methods have been developed to recover a lost mailbox.
Using Exchange 5.5, a common method to recovering a mailbox is to restore a full database backup to a Recovery Server. This method requires a dedicated server which is not affordable to all organizations. In Exchange 2000 and 2003 Microsoft added a Mailbox Recovery feature which allows you to configure a period of time for all deleted mailboxes to remain on the Exchange Server. Normally a setting of 30-days allows plenty of time for a mailbox that was deleted by mistake to be recovered.
Third-party backup vendors, beginning with Exchange 5.5, devised a method of mailbox backup by introducing a second backup pass at the mailbox level. This method uses the Microsoft Message API (MAPI) and is commonly referred to as "Brick-level Backup". The drawback of this method is that the second-pass of the Exchange Database places a very large burden on the Exchange Server CPU. The length of time necessary to perform this brick-level backup is four to eight times the time it takes to perform a full backup. In many cases, the brick-level backup alone can take longer than a 24 hour back up window. Due to these penalties, the majority of users do not perform brick-level backups. They rely on the Mailbox Recovery feature to restore deleted mailboxes in Exchange 2000/2003 and use a Recovery Server in Exchange 5.5. (Figure 1.)
It is very common for end users to delete e-mail by mistake. The Outlook client provides a Deleted Items folder for message recovery, but if this folder is emptied, help is required. No practical tape backup method exists for message level recovery. It is not supported by the Exchange Backup API, and the 3rd-party brick-level backup methods are too slow to be practical. General practice is to configure the Exchange Server Deleted Item Folder to 30 days to allow for message recovery. After 30 days messages are simply not recoverable. Backup tapes can be restored to a Recovery Server for message recovery, but this time consuming process is only practical in special situations or for special individuals (e.g. company executives).
The advantage of tape backup is that the technology is mature, performs well and is fully supported by Microsoft for full Exchange backups. If the Exchange database is not too large (< 40GB) the backup can be performed in a reasonable amount of time allowing for daily full backups. For large databases, incremental backups can be used, but this increases the total recovery time. Tape backups can be transported off-site as a precaution for disaster recovery which is an important feature.
A disadvantage of daily full backups or daily incremental backups is that the amount of data that can be lost is potentially 23 hours of data. The period of time where data is not being protected defines your Recovery Point Objective (RPO). Depending on the needs of your organization, this may be unacceptable. A second disadvantage of tape backup is the slow recovery time. Depending on your backup scheme, tape recovery can take hours increasing your Recovery Time Objective (RTO). If brick level backups are not performed, mailbox or message level restores can take many more hours.
For Exchange protection, traditional tape backup methods provide full Exchange database protection; however they are limited by slow recovery time, a 23-hour recovery point and for all practical purposes no mailbox or message level recovery. As an alternative, new 3rd-party products are entering the market that leverage new disk-based backup methods to reduce recovery time and improve recovery points. The next version of Exchange called "E12" due in 2007 will also include new native backup to disk methods for Exchange protection. Taken all together, these new products indicate that Exchange protection is moving away from scheduled capture to real-time capture of Exchange information. Tape-based information protection remains valuable for off-site disaster protection, but for the best possible service new disk-based approaches are the next best thing for Exchange protection.
Bob Spurzem is a senior product marketing manager at Mimosa Systems Inc.
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|Title Annotation:||Disaster Recovery & Backup/Restore|
|Publication:||Computer Technology Review|
|Date:||Sep 1, 2006|
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