Wednesday, October 10, 2018

How to Get External USB Drives to Work With Macs

External USB drives are used for a variety of reasons, including:
  • Holding copies of files in case a device were to crash or get lost
  • Storing files because a device is low on space
  • Providing quick access to files when the original device is not portable
  • Transferring large files that can be rejected by mail servers
External USB drives are extremely useful. They are reasonably priced, compact, and easy to transport. Additionally, USB drives are fairly universal, connecting quickly without requiring additional software. However, not all USB drives natively operate with full functionality when connected to Mac devices.

How to Get External USB Drives to Work With Macs


There are three file format types supported by Windows machines. The original, FAT, or File Allocation Table, was followed by FAT32, a 32-bit version of FAT, and finally by NTFS, or New Technology File System. In the simplest of terms, each of these protocols are to digital devices what a table of contents is to a book. This means these protocols know where all the information on a drive exists, and without them, it can be impossible to find files without the use of forensic tools.


Typically when an external USB drive is connected to a computer it is identified and usable within a minute. Unfortunately, when connecting to a Mac, the USB device may have only limited access. Checking the permissions of the drive will show read & write permissions, yet trying to write to the device fails. This happens because of a permissions issue that is most likely caused by the device being using NTFS, which is not compatible with a Mac device.

Typical properties on an external USB drive showing read and write access, though files cannot be created here.

Getting the USB drive to be fully functional when connected to a Mac

To change the permissions on the USB drive so it is fully compatible with a Mac, the drive must be reformatted.
  • Open the Launcher app and search for "Disk Utility".  
  • Click on the external drive to view the properties. This should show NTFS as the file system.

  • Click the "Erase" button at the top to reformat the drive with a different format. Be sure the correct device is selected. NOTE: This should only be done if the information on the drive has already been copied off to another location. Do not format a drive unless absolutely certain there is no information on it, or that the information on it has been copied to another location first.

  • In the erase drive window, select the new format type in the drop down list under the drive name. In the example below "ExFAT", which is compatible with a Mac, is selected.
  • Once the correct file format is selected, click the "Erase" button in the bottom corner of the window.

  • Once clicked, the reformat process will begin.

  • When prompted, chose whether or not to use the drive with Time Machine.

  • When the drive has been reformatted, click "Done".

  • In the disk utility window, the external drive is now listed with the new format.

  • Open the Finder app and click on the external USB drive. The properties now show the permissions as custom access.

  • Create a folder to verify the permissions are working correctly.

There are many reasons to use an external USB drive. Whether wanting to keep copies of files, transfer large files or to create storage on a local device, USB drives are typically quick and easy to use. Unfortunately, the default format style works well with a Windows device but is not fully compatible with Mac devices. To fix this, simply reformat the drive into a format native to Mac devices using the steps above. Reformatting the drive will allows it to be used with a Mac device.

As always, knowing how to use the equipment you already have saves time and money!


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