SnapManager uses Eseutil, a Microsoft Exchange utility, to verify the Exchange database files in a backup set. This utility is installed automatically with Microsoft Exchange in the \Exchsrvr\bin directory. SnapManager uses Eseutil to verify the page-level integrity of the databases in a backup and to verify that the databases in a backup and the transaction logs associated with that backup have not incurred physical-level corruption. For more information about physical and logical level corruption, see your Microsoft Exchange documentation.
For more information about how SnapManager checks database integrity in backup sets, see the following topics for more information:
Attention
You are strongly advised to restore only from backups whose databases have been verified. By default SnapManager Restore requires that you restore only from verified backups. However, you can override this requirement. For details, see Overriding database verification during restore.
When you verify the databases in a backup set, Microsoft Eseutil requires that all of the databases files are mounted at the same time. At a more granular level this means that SnapManager, using SnapDrive commands, mounts all the LUNs that contain the backup sets selected for database verification. Each LUN that will be mounted requires one available drive letter or mount point.
To run the Eseutil command, the verification server (whether local or remote) must have a sufficient number of drive letters or mount points available to mount all the LUNs that store the database backup sets you are verifying.
To run database verification against backup sets that are stored on a single LUN or across multiple LUNs, the Exchange server that is used as the verification server must have at least one drive letter or mount point available for every LUN so that the LUNs can be mounted.
To run SnapManager remote verification for more than one backup set in a single job, two unassigned drive letters or mount points must be available. In all other situations, only one unassigned drive letter or mount point is required.
The extra drive letter or mount point is for mounting the LUN in a Snapshot copy that stores the SnapInfo directory for the purpose of transaction log verification (a feature introduced in SnapManager 3.1 for Microsoft Exchange). After SnapManager verifies the transaction logs for the first backup set, it does not dismount LUN or release the assigned drive letter for this LUN. This saves an extra, unnecessary LUN mounting operation for the verification of the transaction log for the second backup set.
Before you perform remote verification for more than one storage group in a single job, check that a second drive letter or mount point is available. If this is not possible, you must schedule the backup or verification jobs to verify one backup set at a time.
Running database verification on a production Exchange server (the Windows host system running the Exchange virtual server used to create the databases) can place a significant load on both the Exchange server and the Data ONTAP storage system. For this reason, verification can degrade Exchange response, particularly during peak work hours.
There are three ways to manage database verification load. The first two methods involve separating the database verification and database backup operations, thereby distributing the load; you can defer database verification, or you can run database verification from another Exchange server. A third method, available only if you are running SnapManager 3.2 with Microsoft Exchange 2003 SP2, is to slow down the database integrity verification process to decrease the load on the Windows host and the storage system.
The following paragraphs describe all three methods of managing database verification load.
By default, a SnapManager full database backup operation runs Eseutil immediately after the backup is finished. Instead of allowing a database backup to automatically verify the databases when the operation is finished, you can disable that feature. You can then run a separate database verification operation any time after the full database backup operation is finished. To perform a deferred verification, select the "Verify databases and transaction logs in the most recent unverified backups" operation in the SnapManager Backup Wizard or the Backup and Verification tab. For details, see Backing up databases.
To prevent database verification from affecting the performance of your production Exchange server, you can run verification on another Exchange server. For details, see Requirements for a remote verification server and Selecting the database verification server.
SnapManager 3.2 introduces a third option for managing database verification, that you can combine with either or both of the existing options, to reduce the load even further. When installed with Microsoft Exchange 2003 Service Pack 2, SnapManager 3.2 supports the ability to throttle Eseutil (the Microsoft Exchange consistency checker utility) in database checksum verification mode so that database verification takes longer to finish. For details, see Configuring Eseutil throttling for database verification.
You can verify the databases in your SnapManager backup sets at various times.
By default, SnapManager verifies the databases in a backup set at the time the backup is created. This is simple and ensures that each database in the backup set is verified. However, this method significantly increases the time required to complete the backup. For a description of how to start or schedule database backup with automatic database verification, see Backing up databases.
With this method, a single operation can be initiated to verify the databases contained in one or more backup sets that have already been created. You can start the verification immediately, or you can schedule the verification to occur later, when it does not affect performance or delay later backups. For a description of how to start or schedule database verification, see Verifying backup databases.
If you attempt to restore from a backup set on which a database consistency check has not been run successfully, SnapManager prompts (but does not require) you to first verify the databases in that backup set. See Importance of verifying databases to be restored.
Note
Database verification is performed on a LUN backed by Snapshot copy. If you take a Snapshot copy of a volume while a LUN backed by Snapshot copy exists, you create a "busy Snapshot copy," which might cause problems when you attempt to delete Snapshot copies. To avoid this, do not schedule backups while a verification is in progress.
Regardless of when you verify the databases in a backup set, the verification can be done on the production Exchange server or on a remote verification system.
In the simplest SnapManager configuration, verification is run from the production Exchange server. However, because the Microsoft Eseutil command used for the verification is CPU-intensive, performing the verification on the production Exchange server host system during peak usage could affect Exchange performance.
Performing the verification on a remote system minimizes the impact of verification on Exchange system resources and backup schedule. To prevent verification from affecting the performance of your production Exchange server, you can run verification on another computer.
SnapManager Restore shows you a list of the backups that have been taken. For each backup, the date and time of the backup is displayed, as well as one of these symbols:
The databases in backups shown with this symbol are verified.
The databases in backups shown with this symbol are not verified.
The databases in backups shown with this symbol failed verification and cannot be restored.
The databases in backups shown with this symbol are verified, but the transaction logs for the backup failed verification. If you need to restore from backups with this symbol, contact technical support.
Note
You can also determine whether the transaction logs for a specific backup have been verified by opening the Restore tab and selecting that backup. The transaction log verification status is displayed as part of the backup information in the right pane.
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Last updated: 28-Mar-2006 11:30:59