Previous 1 2 Next 16 Replies Latest reply: Nov 19, 2012 6:19 PM by Munas
12oz Mouse Level 1 (0 points)

i have lion installed on my macbook and i am about to install mountain lion. im going to do a clean install, i have made a bootable usb and am ready to go. my question is this. if i use disk utility (ran from the USB drive) erase the HD will it remove all the partitions that lion made (the main system partitions and the recovery partition). i want all the data and partitions gone and for the HD to be a "true" blank slate before i install mountain lion (im ocd that way lol)


any info would help, thanks

Mac OS X (10.7.5)
  • Munas Level 4 (1,260 points)

    Disk Utility will not display “Recovery HD” on it’s own because it’s a hidden partition, meaning you can’t just go into the app and delete it. What you can do though is format the entire drive though. This is sort of the nuclear approach but it works to delete the recovery partition too.



    Boot the Mac from a recovery DVD, USB key, or an attached drive

    Launch Disk Utility

    Right-click on the Disk (not the partitions) and select “Erase”

    Select the default Mac OS Extended (Journaled) as the file system, and give the drive a name

    Click on “Erase” to completely format the drive – you will lose all data on the drive and all partitions.This formats the drive giving you a clean slate to start from.


    to make sure you may use terminal command before and after format

    diskutil list

    this will display all the partitions on your disk

  • 12oz Mouse Level 1 (0 points)

    Thanks for the help Munas, i knew that you could not see the hidden partitions from disk utility, what i wanted to know was what was the best way to wipe all those partitions out (hidden or not) and you helped with that.



  • 12oz Mouse Level 1 (0 points)

    follow up question, after i do an erase per instructions diskutil list is showing i have 10 "identifier" partitions, is that normal.

  • Munas Level 4 (1,260 points)

    10 ??? !!!

    just checked my macbook pro runing ML

    it has 5 (I have two patitions) if you use single partition your results should contain 4 after the installation



    Apple_HFS whatever you call it

    Apple_boot Recovery HD

    so since you have nothing on that disk I think it should be 1 or two at most...


    what are the sizes of these partitions and are you sure you are looking to the computer disk partitions and not USB or what you have booted from...?

    How many /dev/diskX you have ?

  • 12oz Mouse Level 1 (0 points)

    ok so



    (Hard drive 250GB)




    Apple_HFS Mac


    (USB Drive 8.1GB)




    Apple_HFS Mac OS X install ESD


    (Dont Know 1.3GB)




    Apple_HFS Mac OS X Base System


    now from this point on

    /dev/disk3 - /dev/disk13    are all untitled partitons rangeing from 524K to 6.3MB

  • Munas Level 4 (1,260 points)

    I think that /dev/disk0 is the disk on your Mac

    all the rest is on your boot device, USB probably...

    check the size of GUID_partition_scheme on /dev/disk0 it should be the size of your Mac disk

    if yes, than your are fine and it is time to start installation

  • 12oz Mouse Level 1 (0 points)

    i editied the info post with the sizes

  • 12oz Mouse Level 1 (0 points)

    i just dont know if those untitled partitions are on that USB drive or on my HD

  • Munas Level 4 (1,260 points)

    is your hard drive size 250GB ?

  • 12oz Mouse Level 1 (0 points)

    i have my orginal snow leopard DVD i guess i could boot from it do an erase and then do a diskutl list and see if those partitions are still there

  • 12oz Mouse Level 1 (0 points)

    yes my HD in my macbook is 250GB

  • Munas Level 4 (1,260 points)

    you may do it as well, however if your mac disk size is 250GB you are good to start installation.

    or you may run disk utility once again and check the sizes and partitions

  • 12oz Mouse Level 1 (0 points)

    ok, thanks for your time Munas i should have it sorted now


    have a good one

  • Munas Level 4 (1,260 points)

    good luck

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