9% of free HDD space just means that your HDD is almost completely full with data such as documents,pictures,videos,music and what not...
Try deleting ALL temporary data and ALL invalid registry using:
-Ccleaner
-Eusing free registry cleaner
-Windows DISK CLEANUP tool
If that did not make a lot of room on your HDD then obviously you have a LOT of data.So:
1. You can leave it where it is and perform the defragmentation anyway,but it will only partially defragment the partition(s) because at least 15% of free space is neccessary to fully defragment the entire partition(s)
2. Move some data to other storage device to have at least 15% of free space so you can fully defragment entire partition(s)
Cheers!