Just to clarify (ignore this if tech bores you), Full reads every byte from alpha to omega in 2MB chunks. If it happens to stumble across a chunk that's all zeroes it makes a 4 byte note in the header and moves on. That's all. It will happily backup a garbage drive, a Windows drive, or anything else. Think dd with some compression. Modified and Truncated backups depend on my ability to read all of the the Ext2 and MFS partitions, then decide which sectors to back up and which ones to ignore. A Full backup of a "dirty" drive will probably be bigger than the source. If you delete all your recordings or even run C&DE it won't help. On the other hand, the drives that TiVo's using right now come from the factory with all zeroes and they only overwrite parts of it or their build process gives the same result. Either way you get giant chunks of naughts that result in a small image. End of the Mythbusters "science" lecture.