If you need to recover a database because a drive failure made your database unusable, you'll probably want to restore as many transactions as possible that finished before the failure. SQL Server Books Online (BOL) says that if the log file is still available (i.e., the disk containing the log wasn't the one that was damaged), you should be able to back up the log records recorded since the last regular log backup. However, SQL Server 7.0 requires that the primary data file also be available. The primary data file contains the information about where the log file is, and if the primary data file was on one of the damaged drives, the log won't be available for backup. In SQL Server 2000, Microsoft has corrected this problem. The information about the physical log file's location is now stored redundantly in the master database, so even if a database's primary data file is unavailable, an administrator can back up the portion of the log that contains the record of transactions right up to the moment of database failure. This final log backup is the last backup you restore to bring the database back to its previous state.
