How to format an external hard drive for your Mac

We’ve run into a couple of instances recently where clients didn’t realize they were using external hard drives that had been formatted for Windows.  The drives they purchased were formatted MS-DOS by default and Disk Utility didn’t pop up.  Thinking all was well, they began copying data to the drives.  The process was slow, laborious, glitchy and they didn’t understand why.

It’s not difficult at all to format a drive for use with your Apple computer.  If you attach an unformatted drive, your Mac will prompt you to open Disk Utility.  If you have a drive that is already formatted (MS-DOS, as in the case above), however, you may not be alerted to open Disk Utility.

Now, if you’re going to be using this drive to move data between Mac and PC computers, then you’ll want the drive formatted for MS-DOS.  It is not advisable to use an MS-DOS formatted drive to store data for your Macintosh computer, as you won’t be able to use the drive to start up your Mac.

If you’re only using the external drive for your Macintosh computer, however, then the ideal is to format the drive for Mac OS X.

**If you have any data on the drive, be sure to copy it to your machine or another device before following the steps below.  Formatting your external drive will erase any data contained on that drive.

1.  Connect the external hard drive that you want to format to your Mac and then go to Finder/Applications/Utilities/Disk Utility

2.  In Disk Utility, you will see on the left a list of hard drives.  Select the drive that you want to format.  The size, brand and model number will typically be listed as the name of the drive.  If a drive has any volumes, they will be indented and listed directly below the name of the drive.  Be sure to select the drive and not the volume in order to reformat the entire drive.

3.  In the right hand section of the window, you will see five tabs — First Aid, Erase, Partition, RAID and Restore.  Click the Partition tab.

  • Alternatively, if you are not going to create partitions, you can just use the Erase function.  This will format the entire drive as well.

4.  Select the Volume Scheme menu on the left and choose the number of partitions you would like to make on your drive.  You have to select at least one partition.

5.  After choosing the number of partitions you want, click the Options button at the bottom of the partition diagram (located under the Volume Scheme pop up menu), which will allow you to select the appropriate partition scheme.

  • Select GUID Partition Table if you want to use the hard drive to start up an Intel-based Mac, or use the drive as a non-startup drive with a machine using OS X version 10.4 or later.
  • Select Apple Partition Map if you want to use the hard drive to start up a PowerPC-based Mac, or use the drive as a non-startup drive with any Mac.

6.  Choose a name and volume format for each partition under Volume Information in the right side of the window.

  • Select Mac OS Extended (Journaled), the default volume format for Mac OS X.

7.  Click the Apply button after you have reviewed your selections.  Another dialog box will appear, confirming that you want to partition your drive.  Select the Partition button and you are finished!

**Big thanks to our brilliant tech Gene for suggesting this post.

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