Optimize using the Cloning Tool

If the Volume Optimization tool reports that the directory of a volume is too fragmented to optimize, you can achieve the same effect using the Volume Cloning tool and an empty partition on an available drive that is large enough to contain all of the data on the volume to be optimized.

Begin by creating an empty partition that is the same size or slightly smaller than the source drive using a program such as Disk Utility. Next, set the Volume Cloning tool to use the File Sync Clone method, with the volume to be optimized as the source and the new partition as the destination. Click Clone to Volume... This process optimizes the data as it is copied.

After cloning is complete, verify the clone by holding 'option' at startup and verify that the clone starts up the Mac as expected. Then, start up from an eDrive to complete the process.

After starting up from the eDrive, return to the Cloning tool, this time selecting the Duplicate Cloning method. Reverse the source and destination, setting the clone as the source and your original hard drive as the destination. Click Clone to Volume... which will restore the data to the original drive, maintaining its optimized state.