In this tutorial, the process to restore corrupt Exchange 2003 database from backup without downtime is explained. It also explains why it is a good plan to collaborate dial-tone database and Recovery Storage Group when restoring backup for any corrupt mailbox store.
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If a large sized Exchange database is corrupt, then restoring from backup depends upon number of factors like network speed, hardware, the backup restoration application used etc. Meanwhile this happens, a DBA has to handle annoyed users and most probably the corporate executive head.
So, basically the target is to recover Exchange mailboxes while the work-flow stays unaffected. For this to happen, the idea is to create a dial-tone database that will help to maintain the messaging service while the old messages and DB can be accessed through OST file (Discussed in later part).
Exchange Dial-Tone Recovery means when the backup is restored, email send-receive process will remain active through an empty mailbox store. Although dial-tone restore technique has been introduced in older versions of Exchange Server but has become more effective in edition 2003 because of Recovery Storage Group.
It is strictly recommended not to delete the database files but move them to different location (if possible on same logical drive) as these files might be needed at some point of recovery. Also, copy transaction logs as they will surely be needed after backup restoration to RSG to bring database to clean shutdown state through soft recovery (which is a process of log file replay).
Soon after this, a message will be prompted on screen. This is because the database files are moved from their original location. Click YES.
Once the dial–tone database is created, it is very important that all users are informed about it as the mailboxes will be empty. The information can be passed through e–mail.
Now, if Outlook 2003 is configured with Exchange Server enabled with Cached Mode option, then if anyone would try to login, they would find following message on screen:
Here, there are two options to choose from:
Click on "Database" tab and enable the check box for "This database can be overwritten by a restore".
Meanwhile, ensure that location of RSG is added according to your requirement.
Note: You cannot select the Public Store option as RSG is not meant for public store recovery.
The State of database should be Clean Shutdown.
If it is Dirty State, then perform soft recovery against the restored DB. For this, LOG files will be needed.
Now, it's the time to swap the RSG with recovered mailbox store with Dial Tone Database. However, we could directly merge both the databases but this practice has certain disadvantages:
Before starting, it is recommended to dismount both the databases from Server using Exchange System Manager (ESM).
Note: This task of swapping DB can be accomplished by changing the logical paths of databases in System Manager. However, that method is not recommended to be used and thus is not shared in this tutorial.
Meanwhile, if the database file names in RSG and Dial-tone DB are not same, it is recommended to rename them (Ensure that no log files has to replayed against both the database after renaming).
In the folders where database files for RSG and Dial Tone DB are stored, create a folder named "UPDATED".
Open ESM, right click on Mailbox Store, and select Properties. In the Database tab, enable the check box for "This database can be overwritten by a restore". Once this is done, mount both the databases on Server.
Before launch of Exchange 2003 SP1, the process of merging two databases was accomplished using Exmerge tool. Nevertheless, with release of this edition, this task was simplified through the feature "Recover Mailbox Data" that can be accessed through Exchange System Manager.
Since we have less in Recovery Storage Group Mailboxes after swapping, we will merge mailboxes from it to Dial-Tone mailbox now.
Thus, through the following steps, restoring the mailboxes data from the crash Mailbox Store is completed as well as the messaged can be easily merged which was received while the user was connected to dial-tone database. Hence, it is called to be as Successful Disaster Recovery. As a better and fast alternative user can use Exchange Recovery Tool for their database files
