It keeps one backup file of each time you build your directory. It backs up the Links, Users, and Category tables. Change the '1' to whatever number you want to use as a backup. 7 is good, 14 is probably over kill -- especially if you put your backups on the same device, or even same computer or controller card.

http://www.postcards.com
FAQ: http://www.postcards.com/FAQ/LinkSQL/