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How long to securely erase (7 pass) 500GB HDD?

S

Steven Jackson

macrumors 6502
Original poster
Dec 8, 2006
387
7
Lincoln, U.K.
Hi,

I have an iMac that I'm about to list for sale. I want to securely erase the HDD and then reinstall OS X from the restore discs.

If I opt for the 7-Pass option (should be enough, there's nothing particularly sensitive on there), how long can I expect the whole procedure to take? Are we measuring in hours or days?

The HDD is 500GB in size.

Thanks for any help you may be able to offer.

Steve.
 
It will be in hours, but I would imagine it getting on 5/6 hours. Basically you are writing 500Gb of data to your hard drive 7 times. I would set it going over night and let it do its thing.
 
A 7-pass wipe is completely unnecessary. It is a myth that you need to overwrite data more than once to make it un-recoverable.

A one pass is enough. There isn't anyone on the planet who could recover any meaningfull data off a hard drive after a one pass wipe. Not even the FBI/CIA/NSA/Military/aliens. No one. It is impossible.

Once is enough.
 
Maximus434 said:
A 7-pass wipe is completely unnecessary. It is a myth that you need to overwrite data more than once to make it un-recoverable.

A one pass is enough. There isn't anyone on the planet who could recover any meaningfull data off a hard drive after a one pass wipe. Not even the FBI/CIA/NSA/Military/aliens. No one. It is impossible.

Once is enough.
Click to expand...

Is this true? Has Disk Utility lied to me? Shocking!

Steve.
 
One pass is enough to prevent even high-end government recovery. 7-pass is insane overkill.

If somebody REALLY wanted your data that badly, they would have taken it by now.
 
Maximus434 said:
A 7-pass wipe is completely unnecessary. It is a myth that you need to overwrite data more than once to make it un-recoverable.

A one pass is enough. There isn't anyone on the planet who could recover any meaningfull data off a hard drive after a one pass wipe. Not even the FBI/CIA/NSA/Military/aliens. No one. It is impossible.

Once is enough.
Click to expand...

300D said:
One pass is enough to prevent even high-end government recovery. 7-pass is insane overkill.

If somebody REALLY wanted your data that badly, they would have taken it by now.
Click to expand...

I don't doubt what either of you are saying, but why do the options for 7-pass and even 33-pass exist if they do nothing? If writing data completely replaces what was there before, why repeat the process 33 times? There must, surely, be some reason for this option...

On a related note, if I follow your advice, would the following be good enough? Boot from install CD, run Disk Utility and erase partition, install OS X, use disk utility to zero-out free space?

Thanks,

Steve.
 
Steven Jackson said:
I don't doubt what either of you are saying, but why do the options for 7-pass and even 33-pass exist if they do nothing? If writing data completely replaces what was there before, why repeat the process 33 times? There must, surely, be some reason for this option...
Click to expand...

Because somehow the idea got around that electron tunneling microscopes/magical beam weapons could theoretically uncover tiny amounts of overwritten data on older harddrives (I'm talking 1980s/1990s) given enough time and money. I say theoretically because no-one has actually done it. This has since been proven impossible anyway. But not before the american dept. of defence got wind of it and decided to overwrite all old hard drives 35 times "just in case". On top of degaussing them, shredding them and then melting them.

It's been the norm ever since (in all over writing software).
 
Steven Jackson said:
but why do the options for 7-pass and even 33-pass exist if they do nothing
Click to expand...
User request, so the insecure paranoid freaks of the world can prevent ANYONE from recovering their checking account records, e-mail password or kiddie porn.

On a related note, if I follow your advice, would the following be good enough? Boot from install CD, run Disk Utility and erase partition, install OS X, use disk utility to zero-out free space?
Click to expand...
Yep. The "Erase and Install" option is the same thing.

Basically, if you need 7+ pass overwrites you're either working on a government project (in which case you wouldn't even be on here asking the question) or you've got some pretty nasty stuff that probably needs to be found by someone...

For Average Joe Blow wanting to protect their accounting records, e-mails and misc. private data on a computer being sold or discarded, a single pass will stop anyone from recovering it. Many people now aren't even including the hard drive with the computer.
 
Maximus434 said:
Because somehow the idea got around that electron tunneling microscopes/magical beam weapons could theoretically uncover tiny amounts of overwritten data on older harddrives (I'm talking 1980s/1990s) given enough time and money. I say theoretically because no-one has actually done it. This has since been proven impossible anyway. But not before the american dept. of defence got wind of it and decided to overwrite all old hard drives 35 times "just in case". On top of degaussing them, shredding them and then melting them.

It's been the norm ever since (in all over writing software).
Click to expand...

Apparently American Intelligence agencies grind down the platters and use them as filler in their new buildings...
 
It is reportedly theoretically possible after a single pass of zeros to recover the old data with laboratory equipment. See http://www.grc.com/sn/sn-134.htm - search for erase.

Leo: Right. Now, practically speaking, who has machinery that even can read it if it's overwritten once?

Steve: Oh, we're not talking some guy in his garage. We're at the NSA sort of level.

Leo: But you are sure such a thing exists?

Steve: Oh, absolutely. It absolutely does.
Click to expand...

Standard DoD 5220.22-M requires a three pass wipe.
 
Agreed, 7 pass is the only way to go. Took about 1 day and 2 hours to get it down on a 500GB HDD under SL.

Just personal bank accounts here, however call me paranoid or not it give me the peace of mind. :D
 
Steven Jackson said:
On a related note, if I follow your advice, would the following be good enough? Boot from install CD, run Disk Utility and erase partition, install OS X, use disk utility to zero-out free space?

Thanks,

Steve.
Click to expand...

Once I get my new iMac, I'll do the same procedure above on my current iMac G5 before selling/donating it away, but after re-installing the 5-year old OS X, should I run the software update for OS X, Safari, etc.?
 
I'm really not sure what the emphasis on multiple wipes is. A single pass is more than sufficient to ensure that your data cannot be recovered. That 7 (or more) passes is required to destroy data so it can't be recovered is nothing more than a myth and it's a pity to see it propagated.

http://www.anti-forensics.com/disk-wiping-one-pass-is-enough
http://www.anti-forensics.com/disk-wiping-one-pass-is-enough-part-2-this-time-with-screenshots

While you wont hurt anything by overwriting more times, your certainly going to waste a lot more of your time as well.
 
NotAHater said:
I'm really not sure what the emphasis on multiple wipes is. A single pass is more than sufficient to ensure that your data cannot be recovered. That 7 (or more) passes is required to destroy data so it can't be recovered is nothing more than a myth and it's a pity to see it propagated.

http://www.anti-forensics.com/disk-wiping-one-pass-is-enough
http://www.anti-forensics.com/disk-wiping-one-pass-is-enough-part-2-this-time-with-screenshots

While you wont hurt anything by overwriting more times, your certainly going to waste a lot more of your time as well.
Click to expand...

Sorry to bring this thread up again, but how do you do a single pass on Mac? Is it just the "Zero Out Data" option? If so, is that really sufficient to wipe your data off of the hard drive (at least with the 7-pass option it writes data all over your hard drive 7 times rather than just zeros once)?

I recall accidentally reformatting my entire hard drive and I was able to recover all of my data perfectly fine with the Data Rescue 3 application.
 
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