FileVault vs File Shredding on an SSD
Most secure delete tools quietly stopped working when Macs moved to SSDs. The reason is physical, it applies to every such tool, and the correct answer is encryption rather than overwriting.
The idea behind file shredding is simple. Deleting a file only removes its directory entry, so the data stays on disk until something overwrites it. A shredder overwrites the contents first, often several times, so recovery tools find nothing.
On a mechanical hard drive that logic held. On an SSD it doesn't, and the reason is worth understanding because it affects every product that claims otherwise.
Why overwriting fails on an SSD
SSDs can't rewrite a block in place. To change data, the controller writes to a fresh block and marks the old one invalid. It also spreads writes across the whole drive so no cells wear out early, a process called wear levelling.
When a shredder asks to overwrite a file, the controller doesn't overwrite the original cells. It writes your zeros somewhere else entirely and leaves the original data sitting in a block that's now marked invalid but not erased. The file system reports success. The old data is still physically present until garbage collection gets round to it, and you've no control over when that happens.
There is also over-provisioning. Every SSD reserves capacity the operating system can't see or address. Data can end up there, and no software running on the host can reach it.
What works
Full disk encryption, turned on before you need it
FileVault encrypts the entire volume. Data written to the drive is ciphertext, including data in blocks you can't address and in over-provisioned space. Without the key, leftover fragments are meaningless.
This is the real answer, and the timing matters. FileVault protects data written after it is enabled. Turn it on now, not on the day you sell the machine.
Check whether it is on:
fdesetup statusErase All Content and Settings, for disposal
On Macs with Apple silicon or a T2 chip, this destroys the encryption keys held in the Secure Enclave. Every block on the drive becomes unrecoverable instantly, regardless of where it physically sits. It takes seconds and it is cryptographically sound.
This is the correct way to wipe a Mac before selling it, and it is far stronger than any multi-pass overwrite. We cover the full process in wiping a Mac before you sell it.
Encrypted disk images, for individual secrets
If the concern is a handful of sensitive documents rather than the whole machine, an encrypted sparse image from Disk Utility gives you a container whose contents are ciphertext at rest.
When shredding still makes sense
It isn't useless. Three cases hold up:
- External mechanical drives. Old spinning USB disks behave the way the original model assumed, and overwriting destroys data there.
- Unencrypted volumes you can't encrypt, such as some shared or removable media, where overwriting is better than nothing.
- Compliance requirements that mandate an overwrite procedure regardless of the underlying physics.
Outside those, on an internal SSD, encryption is the stronger control by a wide margin.
Check your actual protection in one place
CleanMachine reports FileVault status alongside eleven other hardening checks, and its File Shredder states the APFS and SSD limits directly instead of implying guarantees it can't make. Free to scan.
↓ Download Free & ScanWhy so many tools claim otherwise
"Military-grade 7-pass shredding" is easier to sell than "turn on FileVault, which is free and built in". The passes are visible, the progress bar is reassuring, and the underlying limitation requires explaining how flash storage works.
A tool that offers shredding isn't necessarily dishonest. One that offers it without mentioning the SSD caveat is selling reassurance rather than security, and you should treat its other claims with the same scepticism.