Using 'Erase Free Space' on iMac with Fusion Drive in CCleaner for Mac Posted March 11, 2019 9 hours ago, nukecad said: I don't think that it's possible with a fusion drive. Presumably you want to erase the drive because you are selling the Mac? I think that your only option would be to split the fusion drive into a SSD and a HDD. That can be done, (and they can be merged again), but that means reformatting the drives each as a seperate drive, so you would wipe everything on there (including the OS) not just the free space. Of course you would need to re-install the OS again. This recent (Feb 2019) article walks you through the process, read the comments as well:https://www.tech-otaku.com/mac/secure-erasing-mac-fusion-drive/ Ok thank you for taking the time to reply.