SQL Server 2000 has the capability to do snapshot backups, which allows backing up a file or a database with minimal impact on the main system's resources. This is useful not only for making backups, but also for creating a copy of the production database for reporting or testing.
The snapshot feature needs a third-party backup application that supports split-mirror or copy-on-write operations to an appropriate storage device with split mirroring or copy-on-write features. To use the snapshot, either for backup or to copy the database, the backup application typically breaks off one of the mirrors and the data is copied from it while the main storage system and its mirror continue to serve the production database. With copy on write, each block is copied as it is written. In either case, backups kept on disk can be recreated in a matter of seconds. Because SQL Server maintains the history of these snapshot databases, the snapshots can be rolled forward using conventional differential and log backups to keep them synchronized with the main database.
Microsoft discusses the uses of snapshot backups in "Administering SQL Server," a document available from Microsoft at msdn.microsoft.com.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.