2012 MBP no "35-Pass Erase" option?

Discussion in 'Mac OS X Lion (10.7)' started by MacCrank, Jun 11, 2012.

  1. MacCrank, Jun 11, 2012
    Last edited: Jun 11, 2012

    MacCrank macrumors member

    Nov 22, 2011
    just performed the 35pass on my old macbook before thinking of selling and out of curiosity looked at my new MBP settings and noticed it only has 1, 3 or 7. Does this seems right? Why would they not give you the gutmann 35 pass erase as before? How can I get the 35?

  2. Bear macrumors G3

    Jul 23, 2002
    Sol III - Terra
    As I explained in your other thread, it's not needed. One pass is enough.

    If you use FileVault2 full disk encryption, a 1 pass erase is definitely all that's needed. And I use disk encryption in case a drive fails and I can't erase it.
  3. Mr. Retrofire macrumors 603

    Mr. Retrofire

    Mar 2, 2010
    I see two errors:
    1. SSDs only need one pass of random data (to avoid the SSD-controller data compression) and one pass of zeroes (to make your first pass "invisible"). Anything more is a waste of time. They do not work like HDDs. And even for HDDs, one pass of zeroes is enough.
    2. You overwrite only the free space. You should erase the entire disk (boot from your boot-DVD or USB flash drive with Snow Leopard or Lion), not only the free space.

    The 35-Gutmann option is not appropriate for modern (after the year 2000) high density HDDs and SSDs. And do not believe everything what you read about DoD-standards. Many are obsolete.


    You can use encrypted disk images, if you do not need the full disk encryption.
  4. Riemann Zeta macrumors 6502a

    Feb 12, 2008
    As has been mentioned above, if you have a physical spinning disc HDD, there is absolutely no reason why 35-passes would ever be needed. The whole "Gutmann" algorithm and the risk of "ghost magnetic signatures" that remain associated with an HDD sector after a rewrite operation is an urban myth.

    On an SSD, however, there is no way of securely erasing a single file, as: (1) flash cells are never overwritten until every single cell on the array has been used at least once (so using the "Secure Erase Trash" command wouldn't overwrite the file, but instead would write zeros to random cells on the SSD and relink the file LBA to those zeros) and (2) there could be hundreds of copies of that one file on the SSD, including ones in user- and OS-inaccessible slack space, due to write amplification. For an SSD, I'm not sure how to securely erase the whole disc, but most manufactures have a LiveCD boot utility that can perform a "factory reinitialize" of the SSD.

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