A normal erase doesn’t remove your files. When you erase a hard drive, SD card or USB stick in Disk Utility, or format it in a camera, macOS writes a new, empty file list and leaves everything else where it was. Anyone with a free recovery app can find most of the old photos and documents. To wipe a drive before you sell it or give it away, the old data has to be written over, every part of the drive, at least once.
How you do that depends on the kind of drive. Hard drives, SD cards and USB sticks can be written over in full. SSDs can’t be wiped reliably that way, because they move data around inside, so they need a different approach.
What works for each kind of drive
| Drive | Normal erase | What to do |
|---|---|---|
| External hard drive | Old data stays | Write zeros over the whole drive once |
| SD or microSD card | Old data stays | Write over the whole card, then format it in the camera |
| USB stick | Old data stays | Write over the whole stick |
| External SSD | Varies | Erase, then check; encrypt from the start next time |
| Your Mac’s built-in disk | Handled by macOS | Use Erase All Content and Settings |
With Disk Utility (built in)
- Back up anything you want to keep. This deletes everything on the drive.
- Open Applications ▸ Utilities ▸ Disk Utility and choose View ▸ Show All Devices.
- Select the drive itself (the top line, not the volume indented under it) and click Erase.
- Choose a name, a format (ExFAT for a card or stick used with other devices) and GUID Partition Map as the scheme.
- If a Security Options button appears, click it and move the slider to write over the data at least once. Then click Erase.
Apple notes that Security Options are available only for some storage devices, and never for SSDs. On recent versions of macOS the button often doesn’t appear even for hard drives. Without it, Disk Utility’s erase is a quick erase, and the old data is still on the drive.
In Terminal, for a hard drive
The diskutil command can still write over a whole drive. Run diskutil list to find the drive’s identifier (for example disk4), check it twice, then run diskutil secureErase 0 disk4. Level 0 writes one pass of zeros, which is enough for a modern hard drive. Picking the wrong disk erases it, so be certain before you press Return. Afterwards the drive has no format at all; erase it in Disk Utility to use it again. Apple’s diskutil manual warns that this kind of erase can’t fully reach drives with wear leveling, such as flash storage, and recommends encryption instead.
For an SD card
The SD Association’s free SD Memory Card Formatter for Mac has an Overwrite format option that writes over the whole card. Afterwards, format the card again in the camera it’ll be used in. Cards are flash memory, so blocks the card has retired from use can keep old data, but no app can read them through a card reader; only a lab taking the card apart could.
With Reco’s Forget for Good
Reco, a free Mac app, includes Forget for Good. Drop a whole drive, card or USB stick on it and Reco writes zeros over every byte, including the empty space where deleted files were, then formats it again with the same name.
- Open Reco and choose Forget for Good from More ways Reco can help or the Tools menu.
- Drag the drive onto it. Reco says plainly that every file on it will be deleted, and asks you to confirm.
- Enter your password once when macOS asks. Reco shows progress and the time left, and keeps your Mac awake. Keep the drive plugged in.
A 1 TB hard drive takes a few hours; a small card takes minutes. In our test on a 1 TB drive, a full deep scan afterwards found 0 files. Stopping part-way still formats the drive, and what was written over by then is gone. It works on drives formatted as ExFAT, MS-DOS (FAT32) or Mac OS Extended. For an APFS drive, Reco asks you to erase it in Disk Utility instead; it doesn’t clear NTFS drives or your Mac’s startup disk.
External SSDs
SSDs spread writes across spare memory the computer can’t reach, so writing over an SSD can’t promise to reach every old copy. Reco says so rather than claim otherwise. What you can do:
- Erase it in Disk Utility. Many SSDs then clear the freed space themselves (TRIM), but not every external SSD gets TRIM from macOS.
- See whether the maker offers a secure-erase or sanitize tool for that model.
- Check the result with a recovery scan (below).
- Next time, follow Apple’s advice and use the drive encrypted from the start. Erasing an encrypted drive leaves nothing readable without the password.
Your Mac’s own disk
To sell or give away a Mac with Apple silicon or a T2 chip, use System Settings ▸ General ▸ Transfer or Reset ▸ Erase All Content and Settings. The built-in disk is always encrypted, and this destroys the keys, so nothing on it can be read afterwards.
Check that it worked
The only way to be sure is to look the way a buyer could. Reco’s Before You Pass It On uses a quick scan to show how many deleted files a stranger could still recover, writes over the drive’s empty space (where those deleted files were) while leaving the files you can see alone, then looks again, so you see the before and after yourself. It’s for drives you want to keep using as they are; on an SSD it warns that writing over empty space can’t reach every old copy. You can also run a full deep scan from Reco’s main screen, which reads every part of the drive.
Questions
Does erasing a drive in Disk Utility delete the data permanently?
Not on hard drives, SD cards and USB sticks. A normal erase writes a new, empty file list and leaves the old data in place, so a recovery app can find most of it. It has to be written over to be gone.
Where are Security Options in Disk Utility?
In the Erase window, when the drive supports it. Apple says they are available only for some storage devices and never for SSDs, and on recent versions of macOS the button often doesn’t appear at all. Terminal’s diskutil secureErase still writes over a whole hard drive.
How do I securely erase an external SSD on a Mac?
Writing over an SSD can’t be guaranteed to reach every old copy, because the drive moves data around inside. Erase it in Disk Utility, then check with a recovery app. For the future, Apple suggests encrypting an SSD from the start, so erasing it later leaves nothing readable.
How many passes do I need to wipe a hard drive?
One pass of zeros is enough for a modern hard drive: no software can read data that has been written over once. Extra passes take much longer and add little.
How can I check that a drive is really empty?
Scan it with a data recovery app, the way a buyer could. Reco’s Before You Pass It On counts what a stranger could recover before and after clearing, so you see the difference yourself.