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Technical Question How to be sure one has securely erased a hard disc drive?

Asher Kelman

OPF Owner/Editor-in-Chief
Of course it all depends on why the drive needs to be erased. You may add more categories:

  1. Repurposing for new data
  2. Giving away of selling the computer of excess drives
  3. Cleaning up one's drive of unwisely saved sensitive correspondence or images
  4. Simple privacy concerns
  5. Having a pristine drive for new critical data

I am interested in option #5 because I am helping refine a wonderful Mac file copy utility and need to be certain that any files found "out of place" came from some "leakage" in the software's sorting process and not my previously used hard disk drive.

So what do you think is sufficient?

Numbers of passes writing new data and are zeros sufficient? Would using random ASCII have advantages?


Asher Kelman

OPF Owner/Editor-in-Chief
So here is what I am using:

Do you think just one pass of zeros would suffice?

Last edited:

Asher Kelman

OPF Owner/Editor-in-Chief
Great link, Jerome. You are do damn efficient! Yes, the platters need to be destroyed too!

What I discovered, (and contrary to many web blogs, including Reddit), a string of zeros written across the entire drive, (using Techtool Pro), seemed fine. However, data recovery software Disc Drill, (after 1 hour of no progress) then recovered 1 TB of perfectly good image files! I didn’t keepnit going for the required next 11 hours to recover the remains 9 TB, but just the first 1TB surprised me!

Modern drives are so well made that the data is easily recovered even after one wipe!


Doug Kerr

Active member
One of my former clients (whose three initials I won't mention here) had (a couple of decades ago) lovely machines that took a hard drive that was being "retired" and chopped it all up into tiny pieces.

Best regards,


Asher Kelman

OPF Owner/Editor-in-Chief
Who would even imagine that a scheme for using magnetic change on a microscopic level to not only work so well in storing data but be so hard to erase.

The very notion of the recording system seems so trivially naive. I wonder how many folk laughed at the idea when it was first presented?