volume has 22% free space, but only 13% is available for use by Disk Defragmenter
I have recently converted a FAT volume to NDIS using the command line utility convert. The volume is a data disk not a system disk. It does not have page files on it. Explorer reports 22% free. So does Disk Defragmenter in the overview. When you analyze the disk, a lot of space is displayed in the colour of System files. I suspect that this is the 9% of the volume that is 'free space, but is not available for use by disk defragmenter'. I award 500 points to the first solution that allows me to make that free space available - without earsing or formatting the disk, without data loss. Perhaps extra for a good explanation.