Erasing my entire SSD from disk utility - is this normal??

Discussion in 'MacBook Pro' started by mbpkid3393, Aug 12, 2013.

  1. mbpkid3393 macrumors newbie

    Joined:
    Aug 12, 2013
    #1
    Hey everyone. So I'm selling my late 2011 MBP and decided to erase the SSD for security purposes. After booting with Command + R, I opened disk utility and went through the process of erasing the SSD and securely erasing with a 7 pass + erase free space. On the side of disk utility, it shows the drive has 121 gb of memory. The machine is advertised as having 128 gb, and I know it truly has 120 gb of usable space out of the box. So am I truly erasing anything I ever put on the machine? I did make a couple partitions at one point, and just want to make sure those are being deleted as well. This is what my disk utility looks like:
     

    Attached Files:

  2. borgqueens, Aug 13, 2013
    Last edited: Aug 13, 2013

    borgqueens macrumors member

    borgqueens

    Joined:
    Aug 10, 2013
    Location:
    Denmark
    #2
    As my understanding of how computers in general works. (I´m not an pro computer tech dude or anything)
    What you do when erasing, deleting or formatting and HDD and maybe same goes for SSD not sure but it stands to my why not.
    You are overwriting all the binary 1 to 0 when formatting
    when deleting files the file name is altered so the computer do not recognize it anymore and therefore it is still there somehow but you can use the "free space" for another file.

    I belive that the info will always be on the SSD but it will very hard to find and recover it after formatting the SSD.
    But don´t worry about anyone getting your secret files from the disk, they have to be very smart to get it and have to know that it is justefilerabaul to waist time on. I´ll say it not likely to happen if those who get there hands on it don´t know who you are and if they don´t think they will find state secrets on it.

    So to sum up:
    I do not belive it is something you need to worry about to much. If you do think it is a risk you might which to swop the SSD to a new on. However I personal would not worry much.


    If someone for any reason did try to recover anything I don not see how they can get your bank account login after formatting your SSD. It is likely they might find your personal pictures and documents but I can not imagine there being anymore then 10 hackers in the world with the skills to recover your bank account password and even if there is hackers with that skill then I´m sure there are more interested in the governments info. Not sure there even are anyone who knows how to do that kind of recovery sounds to me more like something from a Sci-fi movie.
     
  3. robvas macrumors 68020

    Joined:
    Mar 29, 2009
    Location:
    USA
    #3
    On many file systems (such as Windows), when you format a drive you are simply modifying a table that contains all the file information - you are not actually erasing the drive. When you delete a file, you are just removing the reference to the file, not the file itself. That's how you can delete a 2GB file almost instantly as you can a 2MB file.

    I'm not sure if Mac HFS+ works that way or not.

    You can do things like a secure erase which takes longer, but actually overwrites the data, so it can't be recovered. Note that only one pass is required, not 3, or 7, or 35.
     
  4. CausticPuppy macrumors 65816

    Joined:
    May 1, 2012
    #4

    Unfortunately, secure erasing SSD's isn't as straightforward as old hard disks. In fact there's no standard way to do it, and the "legacy" method of writing zero's won't necessarily delete all data, no matter how many passes you use, due to the way SSD's overprovision their space.

    More reading here:

    http://apple.stackexchange.com/ques...ay-to-securely-erase-an-ssd-on-my-macbook-air


    It sounds like booting into the recovery partition and running diskutil might work, although that still won't touch any data that's in the over-provisioned space on the drive.

    Apparently the BEST option is to enable Filevault2 when the machine is brand new and then throw away the encryption key when you want to sell it.

    This is all news to me too-- I'll be removing any SSD's I installed in machines before I sell them, and for my rMBP I'll trade it back in directly to Apple. I don't have anything super top-secret though.

    I wonder if Filevault will make a dent in the awesome SSD performance of the new PCI-e SSD's coming out in this year's Macs?
     
  5. pmau macrumors 65816

    Joined:
    Nov 9, 2010
    #5
    Secure erase will use random data to write each block of your SSD.
    Doing that several times on each block on the SSD is a really bad idea.

    The internal garbage collector has no way of knowing that this is just junk data, and will totally screw up the automatic wear leveling on the SSD.

    Do not ever do that.
     
  6. hammo123 macrumors newbie

    hammo123

    Joined:
    Jun 9, 2013
    #6
    I always use Parted Magic
    It's a free set of utilities you can burn to an .iso disk & boot from on a 2011 Mbp.
    There's a ATA secure erase function which I've read is most effective for SSDs...
    also it only takes a few seconds ..Blam!! everything is gone
    http://partedmagic.com/doku.php?id=downloads
     
  7. mbpkid3393 thread starter macrumors newbie

    Joined:
    Aug 12, 2013
    #7
    From the links you posted it looks like the way I'm doing it has a good chance of working. Again, my question is, is it normal that on the side of disk utility it shows there's 121 gb instead of 128gb? Even if the secure erase doesn't work I want it to try to get everything I ever put on the machine. I'm thinking that those 7gb is the over provisioned state you mentioned, which would lead me to believe that I never used any of those 7 gb correct?
     
  8. robvas macrumors 68020

    Joined:
    Mar 29, 2009
    Location:
    USA
    #8
    GB to GiB = about 7%

    120/128 = 0.9375
     
  9. borgqueens macrumors member

    borgqueens

    Joined:
    Aug 10, 2013
    Location:
    Denmark
    #9
    Perhaps the mac osx utility fills up the rest of the space in a hidden partition on the SSD.
    I know that if you take the SSD out and insert a new on you have to download osx to install it. That must indicate the install files lies on the SSD and not on a ROM as some windows computers in the past have used.

    My conclusion is that the 7 GB you are missing might be the OS X installation files needed to restore OS X to factory settings. Hope this answers your question.
     
  10. mbpkid3393 thread starter macrumors newbie

    Joined:
    Aug 12, 2013
    #10

    So what accounts for the 7% if I'm trying to erase everything?
     
  11. borgqueens macrumors member

    borgqueens

    Joined:
    Aug 10, 2013
    Location:
    Denmark
    #11
    My conclusion is that the 7 GB you are missing might be the OS X installation files needed to restore OS X to factory settings. Hope this answers your question.
     
  12. CausticPuppy macrumors 65816

    Joined:
    May 1, 2012
    #12
    Mac OS X reports GB, not GiB. It's been that way since Snow Leopard. The conversion is not necessary.

    If you look closely at the screenshot at the bottom, you'll see it's showing 120GB = 120 billion bytes or so.

    The missing GB are due to the overprovisioning. If you install the same drive on a Windows machine, it maybe only report 112GiB, vs. 120GB.

    More info:

    http://www.edn.com/design/systems-design/4404566/Understanding-SSD-over-provisioning
     
  13. mbpkid3393 thread starter macrumors newbie

    Joined:
    Aug 12, 2013
    #13
    Ok. Just to clarify, those 7 gb were being used before I ever first used the machine, and therefore none of my stuff ever took up any of those 7 gb? Also, I did mention in the original post that I made a couple partitions at one point on my computer. Are those being erased as well through this process?
     
  14. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #14
    As CausticPuppy mentioned, you are only seeing 120GB due to over provisioning. See my earlier post here. The space set aside for over provisioning is not seen by the OS.

    Some of your data may or may not have been in that space. Lets say a few NAND cells become unstable and the SSD controller marks them as bad. Then what would happen is the firmware would assign some of that over provisioned space to replace the bad NAND cells marked unusable. This way you still have the full 120GB available to use. Think of it as like a spare tire for your car. :)

    If you selected the drive brand at the top in Disk Util when you erased, you wiped all partitions.
     
  15. mbpkid3393 thread starter macrumors newbie

    Joined:
    Aug 12, 2013
    #15

    Thanks for clarifying. I'm guessing there's a very small to no chance none of my info got on those 7 gbs through the process you mentioned. If you look at my screenshot, I'm erasing the one that says "untitled". If I try erasing the 121 gb option, it'll say it can't unmount the disk. I hope that's how it's supposed to work.
     
  16. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #16
    I'm sorry... I missed that you are on the recovery partition.

    It only shows the one partition, so if you had two, they are gone and wiped.
     
  17. mbpkid3393 thread starter macrumors newbie

    Joined:
    Aug 12, 2013
    #17
    Yeah I booted using Command-R. So choosing the 'untitled' in my case is effectively wiping everything, including any partition I made at any point since I don't see it in the sidebar of disk utility?
     
  18. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #18
    Exactly.
     
  19. mbpkid3393 thread starter macrumors newbie

    Joined:
    Aug 12, 2013
    #19


    Thanks. Just out of curiosity, what is "SuperDrive" "disk1" and "Mac OS X Base System"? I know the dmg at the end is the file being created for the erase process. My best guess is that those other three are what takes up that memory and come with the machine.
     
  20. Ichabod. macrumors regular

    Joined:
    Oct 1, 2012
    #20
    SuperDrive is your optical drive. If you put a CD/DVD in your computer, it shows up there in disk utility.
     
  21. Weaselboy Moderator

    Weaselboy

    Staff Member

    Joined:
    Jan 23, 2005
    Location:
    California
    #21
    That is the net boot volume that is created temporarily when you are in recovery. Once you reboot it will go away.
     

Share This Page