MobileMe: Perform a Full Backup when backing up to a rewritable disc
Use Backup's Full Backup Plan when backing up to a rewritable disc (CD-RW or DVD±RW) in order to avoid potential data loss.
To perform a full back up, choose Full Backup from the Plan menu in Backup.
Backup 3 performs incremental backups--backing up only files that have changed since your last backup. This also occurs if you are backing up to a CD-RW or DVD±RW. If you perform a backup to a CD-RW or DVD±RW, and later wish to back up changes that have occurred in your backup set to the same disc, you should perform another Full Backup, rather than a normal backup. Performing a normal backup may lead you to replacing the full backup on your disc with only data that has recently changed.