The larger the SQL Server backup set, the more likely you are to have some kind of error. This isn't to say that
errors are inevitable, but they are more likely to occur during a large backup (1 GB or more). Since restore operations for big backup sets are not trivial (and take a long time), it helps to know if you're dealing with a damaged backup set before investing hours of your time trying to perform the restore. This goes double when trying to restore a database that's already in place and operational.
One way to determine if the backup set is readable without attempting to restore data into a working form -- and without expending a great deal of time -- is to use the RESTORE FILELISTONLY command. When issued through Query Analyzer or a similar tool, it can be used to scan the backup set and return a list of database and log files contained in the backup. SQL Server also has to perform basic integrity checks on the file when it does this, so if there's an error retrieving the file list in the backup set, then the set itself may be damaged. It's best to find out about that sooner rather than later.
The command syntax for this would be something like: RESTORE FILELISTONLY FROM DISK='C:\BACKUPS\DATABASE.BAK'
The name of the file and its location will vary, of course. Note: You may have multiple backup sets in one file. While some may not be recoverable, others may still work. To specify a certain backup set, use the WITH FILE=x parameter at the end of the above command, where x is the number of the backup set in question.
About the author: Serdar Yegulalp is editor of the Windows Power Users Newsletter. Check it out for the latest advice and musings on the world of Windows network administrators -- and please share your thoughts as well!
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