On the DNS-343/323, incremental backup adds new files, but does not remove files deleted from the source Volume, so over time the incremental backup grows progressively larger. Not having peronally tried incremental backup on the DNS-345, I suggest you create a test directory and experiment to see how incremental backup behaves before using it on real data. As a general rule, I recommend this appraoch for all forms of backups to ensure they behave the way they are designed to. Please post back if/after you test this functionality.