Please help: Question about reformatting external HD

Discussion in 'Mac Accessories' started by smallthintiny, Feb 17, 2009.

  1. smallthintiny macrumors newbie

    Feb 17, 2009
    Hi, I have a Lacie 500 GB external HD.

    I just switched from PC to mac and I wan tot reformat my HD so that it is compatible with mac. I went to disk utilities and followed the instructions but when I go to erase it (I choose Mac OS extended journaled) it says:

    Volume Erase failed

    volume erase failed with error:
    could not unmount disk.

    I can't delete things off my HD and I want to so I can make more space!

    How the heck do I fix this?

  2. fawlty macrumors regular

    Jun 17, 2003
    New Zealand
  3. sickmacdoc macrumors 68020


    Jun 14, 2008
    New Hampshire
    Your reformat of a previously PC formatted disk is most likely failing because you need to establish the correct Apple partition map- in spite of the unmounting error noted. This has come up several times and the fix is usually simple.

    To prepare a PC disk for Mac, just do this (takes longer to type out than to do!;)):

    • Restart your system with the external powered up.
    • Start Disk Utility
    • Select your disk in the left column (the whole disk, not a partition which is listed below it)
    • Click the "Partition" tab at the top- not "Erase". "Erase" only clear the data and does not establish the right partition table map.
    • In the partition section, change the "Volume Scheme:" from "Current" to "1 partition" (or however many you want)
    • NOW the important part- click the "Options" button at the bottom. In the window that appears, select "GUID" if you have an Intel based Mac or "Apple Partition Map" if you have an earlier PowerPC based Mac. Click continue.
    • Name the partition or partitions as desired, picking Mac OS Extended (Journaled) in the "Format:" selection of each.
    • Click "Apply" and then "Continue" and sit back. In a short time you will see your HD icon or icons appear on your desktop.

    That should take care of the error, but if not post back and we will come up with something!:)
  4. sickmacdoc macrumors 68020


    Jun 14, 2008
    New Hampshire

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