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Securely erasing all data from a hard drive

I (full) formatted my external hard drive. Now, before giving it to someone else is there anyway to make sure there is no way to retrieve data using some of these recovery software's?

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marked as duplicate by nhinkle Feb 12 '12 at 4:15

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

Which operating system ? –  Karolos Feb 11 '12 at 21:25
If it wasn't being given away, I woulda said to get a shotgun for it... –  Canadian Luke Feb 11 '12 at 21:27
Do we not already have a question on this somewhere? –  Iszi Feb 12 '12 at 4:01
Yup, here it is: superuser.com/questions/4678/… And more: superuser.com/search?q=erase+hard+drive –  Iszi Feb 12 '12 at 4:03

5 Answers 5

up vote 4 down vote accepted

Use Eraser - this free utility will overwrite your entire drive with your choice of patterns - up to and including the 35 pass Guttmann.

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Use Darik's boot and nuke: www.dban.org/ - It's a bootable disk that will run on any system and totally delete selected hard drives in/attached to the system. Just make sure you are deleting the right drive if you have more than one.

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+1. Simple and quick, especially if you have lots of computers to do ALL the data on –  Canadian Luke Feb 11 '12 at 22:24

Reformatting the drive will effectively mean that a typical user who just wants to use the drive won't be able to access the files.

However, there is software available that can recover data from such drives. How much data they get back depends on what's been done to the drive since it was formatted. Overwriting the drive with new meaningless data achieves this.

This article goes into more details and lists some of the software you can use to achieve this. As it says you need to overwrite the data several times to ensure it's completely irrecoverable:

The Gutmann Method

Based on Peter Gutmann's paper "Secure Deletion of Data from Magnetic and Solid-State Memory", this method provides the best security. Data is overwritten 35 times with carefully selected patterns, which makes it unrecoverable. Unfortunately, it also makes it time consuming.

US DoD 5220-22.M

Based on the United States Department of Defense recommendation 5220-22.M, this method overwrites the data seven times. While less secure than the Gutmann method, it is faster.

However, other evidence shows that this might well be overkill and that a single pass of pseudo random data is enough.

The article ends with a technique to ensure that your data remains deleted forever:

  1. Remove the hard disk from the computer
  2. Unscrew the casing, exposing the disks
  3. Smash them to smithereens
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35 passes are not needed (even Gutmann himself states so). In fact, you very likely are okay with just one psuedorandom pass. See also this question. –  Andrew Marshall Feb 11 '12 at 21:54
@AndrewMarshall - That's a quote from the article, not my words :) –  ChrisF Feb 11 '12 at 21:57
And that article is somehow infallible? Gutmann himself states, as I referenced above, "it will have no more effect than a simple scrubbing with random data". –  Andrew Marshall Feb 11 '12 at 22:03
+1 for SMASH THEM –  goblinbox Feb 11 '12 at 22:30
Smash them -> pieces could be reconstructed. Much better to melt them. –  thefinn93 Feb 11 '12 at 22:52

Data may be recoverable if you simply formatted or 0'd the drive.

In linux use srm, included in the secure-delete package.
In OS X, cli srm is available, but disk utility may be more convenient and has the same effect.

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On Windows, you can run diskpart and use the clean all command. This will zero out the drive.

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