Drive Genius 3’s Repartition is an easy to use tool that allows you to resize and manage partitions on your Mac hard drives without having to erase the entire drive or lose data already on the drive. Today I helped a customer that wanted to shrink one of his partitions using Drive Genius 3 so that he could add another partition. When he went to resize the partition in Drive Genius 3 he received an error that there was not enough contiguous free space and was asked to Defrag the partition first.