We currently run local backups to tape at eight manufacturing locations (Arcserv 11). We are contemplating centralizing backups to the corporate office with a SAN. We would like to do nightly backups to a disk array, then a backup to tape at the end of the week. After the initial full backup how do we maintain a full backup of all the data on the disk array without doing another full backup across the WAN from each location at the end of each week.