External Harddrive says: Read Only

Discussion in 'Mac Basics and Help' started by chewsa, Apr 7, 2009.

  1. chewsa macrumors newbie

    Apr 7, 2009
    I plugged my Cosmos Mobile storage USB external harddrive into my computer. When reading the installation instructions it says that MacOS 9.0 or higher will simply recognize it. I have 10.4 and it recognizes it but wont let me put anything on it...it says read only. I need to back up my files. I am a junior college student and cannot afford to loose ANYTHING!

    Please Help!
  2. kastenbrust macrumors 68030


    Dec 26, 2008
    North Korea
    How is the external hard drive formatted? HFS+? NTFS? FAT? FAT32?

    (if you dont know, tell me, has it been used with a Windows machine before?)
  3. Seyyerin macrumors newbie


    Mar 16, 2009
    about the above

    IF it does read NTFS you can easily make it so you can read/write. Go to applications, then to utilities, then to disk utility, then once there click on the HD. Once there, go to the Erase tab, and click volume format and change it to MS-DOS(FAT), the name doesn't matter. Windows will be able to write and read to that format as well but the size of individual files that can be copied onto fat32 i think is somewhere around like 4.5 gigs.
  4. BlueRevolution macrumors 603


    Jul 26, 2004
    Montreal, QC
    Of course, formatting the drive to FAT32 will also erase all data already on there.

    The file size limit with FAT32 is 4.00 GB.

    If you want read/write access to NTFS-formatted drives, you can do so by installing MacFUSE and NTFS-3G.
  5. Cave Man macrumors 604

    Cave Man

    Feb 12, 2007
    Neander Valley, Germany; just outside Duesseldorf
    The drive is NTFS initialized at the factory. If you want to use it as a Mac volume, you need to open Disk Utility, select the drive (and not the partition indented and below it) and initialize it. Use the Partition tab if you want more options.

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