O&O Defrag 17 Product manual

O&O Defrag 17 
Free space needed for defragmentation

The following limitations are valid for O&O Defrag. These are caused by Windows and cannot be circumvented.

Size of Drive

All drive sizes supported by Windows are supported by O&O Defrag.

O&O Defrag was optimized for use on file systems having an especially large number of files. The storage capacity of a drive is therefore irrelevant.


Any number of folders can be defragmented. O&O Defrag has an optimized memory management which allows it to record all file and folder information.

Free hard disk space

Drives without any free disk space cannot be defragmented. For the best possible results, at least 5% of the whole hard disk capacity should be free. Files larger than the maximum free and connected storage space, may not be possible to defragment, and if so only with several runs.

To accelerate defragmentation, we recommend reserving at least 10-15% free hard disk space, however, this percentage decreases the higher the hard disk size is. What really matters is the size of the largest file that needs to be defragmented or moved around. For an optimal defragmentation, the file should have enough connected storage space available.