Problem Summary. In attempting to format (initialize) a Western Digital large capacity drive on an Apple computer, you may get an unknown error.

Problem Solution. The instructions below will resolve the problem. However, any data on the drive will be lost, including the original software that came with the drive, so you may want to copy that before continuing.

  1. Run the Apple Disk Utility found in Macintosh HD > Applications > Utilities.
  2. Click to select the drive you would like to format (initialize). The drives are listed on the left.
  3. Click on the Partition tab.
  4. Click on the Volume Scheme drop down selection menu and choose the number of partitions you want (this is usually 1, unless you would like separate drives listed for storage when you plug this drive in).
  5. The Options button will become available. The default setting for the Western Digital drive will be Master Boot Record. Change this to Apple Partition Map (for greatest compatibility with older Apple computers) or use the GUID Partition Table (which works with more recent Apple computers).
  6. Provide a name for your drive (partition) and then click on the Apply button.
  7. Your drive will be formatted (initialized).

Time Machine Backup. The above process is performed automatically when the drive is first installed if you indicate that you would like to use the drive with the Time Machine backup software.

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