Safe delete

TechToolPro13 for one App...

If you’re on an SSD or other flash storage device, all deleted files are automatically erased.

That’s fundamentally how SSD and all flash storage works.

The hard disk drive concepts of data remanence or of scrounging free space from deleted files effectively doesn’t exist.

Before any freed storage can be re-used, a. SSD or other flash storage device must first erase that storage.

There is a very short window when that data might be around, but for most of us that’s a negligible risk. A hypothetical attacker would have to power down your storage immediately after the delete and keep it powered down, and they’d have to catch enough “interesting” deleted contents in flight to matter, and they’d need direct access into the SSD or flash storage hardware. All SSD and all flash storage works very quickly to get deleted or “overwritten” storage back into the pool of available free storage; just as fast as the SSD or flash device can internally erase and ready the storage for re-use.

Complicating this whole discussion for those that remember overwriting, it is not possible to overwrite sectors of storage on an SSD or other flash storage. An “overwrite” frees the storage and which then goes through the erasure process, and the new data is written to a new storage location elsewhere on the SSD or flash storage device. This both for performance reasons—erasure is comparatively slow, hence the pool of free storage and the use of what’s called over-provisioning and which is “extra” storage intended to mask failed storage areas, spare sectors—and for wear leveling, to distribute writes and erasures across all available free space and to avoid repeatedly re-using and wearing out specific sections of SSD or flash storage cells.

Hard disk drives also use over-provisioning and spare sectors. This for the same reason as SSDs and flash storage, too; to present a logically perfect device, given the near inevitability that some number of sectors will fail.

I do not recommend cleaner apps, not add-on anti-malware apps.

i do strongly recommend that storage encryption be enabled. This for hard disk storage, as well as SSD and other flash storage devices. This to protect your data when your storage is eventually replaced, or when your storage is retired. This for the then-current contents of your hard disk or SSD or flash storage. Encryption also protects against the exposure of any data remaining in a failed sector. Again, there’s no storage-overwrite function available on SSD and flash, which means you’ll need to write a whole lot of data to erase all storage (including overwriting the over-provisioned storage) by running all storage and all over-provisioned storage through the erasure-and-reuse sequence, and a failing or failed storage device or failed sector of storage may not permit even that across hard disk or SSD or flash.

Some other options, with varying costs...

Upgrade the HDD to an SSD. An Apple authorized repair provider might be willing to swap in an SSD, as some repair providers have done. Vastly faster, too.

If you have enough storage, set up separate encrypted partitions. I don’t like using partitions, but it’ll work.

It’s been a while since I’ve needed this, but secureErase single-pass might be an option prior to logout.

diskutil secureErase freespace 0 “/Volumes/Your Volume Name Here”

Keep the sensitive stuff on your own removal storage, and encrypt that.

Require the other folks to bring their own external storage, and require them to boot and run from that.

...Direct access to a computer opens up a whole pile of other risks beyond mundane disk scavenging, of course.