I am experiencing huge problems with a harddisk that contains a lot of highly compresses files (on filesystem level). Example: The disk is 350GB, has 280GB free space and contains 400GB of data (as I said, the files are highly compressed). All calculations of Defraggler are totally wrong, speed is extremely poor. It looks like Defraggler is looking for free space for the new file, but BASED ON THE REAL FILESIZE, not based on the COMPRESSED size (i.e. the required space). I do