Macbook does not read an external WD hard drive

macOS Mac does not recognize hard drive - what to do?

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Everyone who uses a computer fears this problem: A hard drive with important data is connected and nothing happens. The Mac just doesn't want to find or address the drive. There could be a number of causes that should be investigated in turn. If you are unlucky, the data is gone - but that is only the very last consequence. We help with troubleshooting. But first you should see what happens when you connect the hard drive to your Mac:

What happens when you connect?

First, connect the hard drive to your Mac. Hard disks and USB sticks usually have small LEDs that indicate the operating status. With mechanical hard drives, you can also hear whether the device is running. Notice whether the LED is lit or blinking. If nothing happens, i.e. no lighting or blinking and no sound, there are four possible causes:

  1. The power supply is too weak.
  2. The Mac USB port is bad.
  3. The cable is broken.
  4. The hard disk is defective.

Hard drive is not recognized: hardware troubleshooting

In order to check what the problem is, you should first carry out the following steps to diagnose the problem:

  1. First disconnect all other USB and Thunderbolt devices from your Mac in order to rule out sources of error.
  2. If you have a Macbook (Pro), you should also ensure that there is sufficient power at the USB port: Connect the notebook to the power supply unit.
  3. Now restart the Mac once.
  4. If the hard drive has its own power supply unit, connect it to the power supply as well.
  5. Check that the cable is properly seated on the hard drive.
  6. Then connect the hard drive to your Mac.
  7. If that doesn't change anything, you'll need to plug the hard drive into a different USB port on the Mac. Avoid hubs or adapters in order to reduce possible sources of error.
  8. If still nothing happens, you should connect the hard drive to another PC or Mac. If it goes here, it is due to your Mac: There may be an error in the USB controller.
  9. If the LED does not light up on the other PC either, there are two possibilities: Either the cable is defective - or the hard disk.
  10. Try a different cable. If nothing happens, the hard drive is probably broken.

Hard drive is not recognized on the Mac: software troubleshooting

If the LED on the hard drive or USB stick lights up and a hardware defect can be ruled out, the power supply has stopped. If it flashes briefly, the Mac has spoken to you. If it is still not displayed, there may be a software error:

  1. Restart the Mac and see if the drive mounts afterwards.
  2. To do this, open a Finder window. The disk should be displayed here.
  3. If it doesn't, open Disk Utility from / Applications / Utilities / and see if the disk shows up here.
  4. Click the hard drive. It may not be formatted correctly. MacOS can read many hard disk formats, but not all of them (e.g. from Linux).
  5. Format the hard disk with the "Erase" button. Danger: All data on the data carrier will be lost!
  6. Use the following settings for hard drives that you only use for macOS: Format: Mac OS Extendet (journaled) and Scheme: GUID.
  7. Use the format: ExFAT and the scheme: Master Boot Record for hard disks that you want to use for exchange with Windows.
  8. Then click on "Delete". The hard drive should then be usable.
  9. If an error message occurs while formatting, there is probably a defect on the hard disk. Exchange them.