I added a 160Gig internal HDD to the server for the Server Backup feature and only backup the OS to that drive (relying on DrivePool duplication to preserve client data). Initial backup of the OS took about 16 gig, and subsequent backups are very minute. So I'm assuming that the Server backup works the same as client backups, adding only what has changed since last backup.
I can't find any info on how to manage that backup disk, or what will happen when it fills up. Is there a way to specify how long to keep the backups, etc?