The following is tip #13 from "20 tips on protecting and recovering Exchange data in 20 minutes," excerpted from the book, "Mission Critical Microsoft Exchange 2003" (Digital Press, a division of Elsevier, Copyright 2004). For more information about this book and other computing titles, please click here. Return to the main page for more tips on this topic.
By reading the beginning of the backup set, the backup application gets a list of databases that are available. Once the administrator selects the correct database to be recovered, the backup application begins by making ESE API calls to start the restore.
First, the backup application asks the administrator for inputs, such as the server to restore to, the location and a temporary directory for the log, patch (if applicable) and restore.env files.
The backup application makes the HrESERestoreOpen call to gather this information and then the HrESERestoreAddDatabase call once for each database that is going to be restored. At this point, ESE leaves it to the backup application to restore the needed database files to the proper locations. ESE does not get involved much in copying the database files to disk from the backup set. ESE allows the backup application to make Win32 file system calls directly to the operating system and copy the files.
The reason for ESE's lack of involvement is based on the reasoning that the database files have already been checksummed when they were backed up, and if the backup set is complete, the databases should be intact. There is no reason for ESE to check the database integrity when it is being restored. Since the databases being restored are dismounted (i.e., not open files), it is much simpler and faster to have the backup application copy these files directly to disk.
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About the author: Jerry Cochran is a contributing editor for Windows IT Pro and Exchange & Outlook Administrator and a group program manager for Microsoft. He is the author of Mission-Critical Microsoft Exchange 2000 (Digital Press).