http://ssd.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/zh-hans/module/how-delete-your-data-securely-macos
These instructions apply only to traditional disk drives, and not to Solid State Drives (SSDs), which are standard in modern computers, USB keys/USB thumb drives, or SD cards/flash memory cards. Secure deletion on SSDs, USB flash drives, and SD cards is very hard! This is because these types of drives use a technique called wear leveling and do not provide low-level access to the bits as stored on the drive.