Volume shadow copy overview
Windows XP allows you to create shadow copy backups of volumes, exact point-in-time copies of files, including all open files. For example, databases that are held open exclusively and files that are open due to operator or system activity are backed up during a volume shadow copy backup. In this way, files that have changed during the backup window are copied correctly.
Shadow copy backups ensure that:
Applications can continue to write data to the volume during a backup.
Files that are open are no longer omitted during a backup.
Backups can be performed at any time, without locking out users.