Reformatting Mac with a "7-Pass Erase".

Discussion in 'Mac Basics and Help' started by BFM, May 27, 2009.

  1. BFM macrumors newbie

    Joined:
    May 27, 2009
    #1
    I currently have my internal HD partitioned into two chunks. One runs my OS and the other is an old Windows/storage partition. I'm running a MacBook Pro 2.2 Intel Core 2 Duo.

    I have a plan and I want to check if any one here thinks there will be a problem, or might have another suggestion.

    I want to do the "7-Pass Erase" on the second "storage" partition. Totally clean it up. Then do a complete install of the OS from DVD onto that partition. Using Boot Camp, start the Mac up on that second partition and do the "7-Pass Erase" on the "old' OS number 1 partition. Then I'll be running my OS on the second "old storage" partition.

    Dose any one see a problem with that? Dose it make sense? Is there another way to do a complete "7-Pass Erase" on the entire drive. I have very sensitive information I need to be sure is deleted, and I'm lending on my system for a couple months.

    Also, will 13 GB cover the install of the OS on my second partition?

    Thank-you so much. :)
     
  2. Guiyon macrumors 6502a

    Joined:
    Mar 19, 2008
    Location:
    North Shore, MA
    #2
    It would be much easier just to boot off the install DVD, open the "Tools" menu, launch "Disk Utility" then run the erase, and you can skip over the rather complex plan you currently have.
     
  3. BFM thread starter macrumors newbie

    Joined:
    May 27, 2009
    #3
    Really?

    Really? You can do the "7-Pass Erase" from the install DVD?

    This is totally a better plan and the main reason why I posted this question. I'm new to mac. You saved me many hours. Big Thanks.
     
  4. ortuno2k macrumors 6502a

    Joined:
    Nov 4, 2005
    Location:
    Hollywood, FL
    #4
    Yes, this can be done from the DVD Setup. But unless you're selling or donating your Mac, I'd refrain from doing the 7-pass erase and sit there for hours and hours on end waiting for it to finish.
    You can do fine with the quicker option that doesn't take as long. I've done it many times and never had a problem.
     
  5. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #5
    As said, Disk Utility from the install DVD will do this fine.

    However, why are you set on a 7-pass erase? Unless you work for the CIA a single-pass erase ("write zeros") is more than enough security.

    The idea that data can be retrieved even after being overwritten in a single pass has recently been questioned by a paper I read, and even if it could, you're talking about a procedure that would cost thousands of dollars if not more.

    Note, by the way, that if you're just trying to really clean the drive, and security isn't the issue, then even a single write zeros pass is massive overkill--simply reformatting the partition/drive is just as good for any practical reason.
     
  6. Jethryn Freyman macrumors 68020

    Jethryn Freyman

    Joined:
    Aug 9, 2007
    Location:
    Australia
    #6
    If you're just doing a fresh install, zero the disk.

    I you've got sensitive information and are lending it out, do the 7 pass erase. That way there's absolutely no chance of it being recovered with current technology.
     
  7. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #7
    Just to follow up my previous assertion, I wanted to add some more concrete detail about the whole multi-pass erase thing:

    Note that the notion of multi-pass erases is almost entirely based on a 1996 paper (this is specifically where the 35-pass erase came from, and why it's called Gutmann):
    http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html

    The 7-pass is specifically due to a US Department of Defense security requirement that was created, I believe, based on the assumptions of that paper. (As Apple explains.)

    Importantly, hard drive density has increased by a factor of well over 100 since 1996, and the technology used to store data has changed significantly. To quote the more recent addendum by the author of the above paper:
    In a more recent footnote, he even more explicitly says:
    Point here being that in real life in the modern era, even WITH massive superspy technology the chances of retrieving any usable data from a single-pass wiped drive are near zero, and unless you work for the CIA the practical chance of that kind of technology getting anywhere near your hard drive is even less.

    So while Apple may slap a 7-pass-erase feature in there to deal with old DoD requirements, for any reasonable person a single-pass erase is plenty. Also note, by the way, that if it's top secret data, the only security accepted by the US government is physically grinding the drive into little pieces.
     
  8. Ttownbeast macrumors 65816

    Joined:
    May 10, 2009
    #8
    Ive always thought the 7 pass or 35 pass erase was only neccessary when I was hiding evidence of porn from an ex gf with computer skills LOL
     
  9. Jethryn Freyman macrumors 68020

    Jethryn Freyman

    Joined:
    Aug 9, 2007
    Location:
    Australia
    #9
    To prevent recovery with a software utility, only a single pass is needed.

    The only way to recover an overwritten file is with magnetic force microscopy.

    The longest intact overwritten file recovered with 100% accuracy was 4KB in size.
     
  10. MikhailT macrumors 601

    Joined:
    Nov 12, 2007
    #10
    Even a magnetic force microscopy isn't a sure way, that's the same as using a tweezer to pick up a needle in a haystack.


    7 pass secure erase is just to put your mind at ease, it never hurts to just do it. 1 pass is often enough.
     
  11. MarkMS macrumors 6502a

    Joined:
    Aug 30, 2006
    #11
    Yeah, I just use the 7-pass erase when I sell my computers online. If I'm giving it away to a relative, I just do a single pass. Even if research says one pass is enough, I still feel better running a 7-pass. Old habits die hard.
     

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