How To Format An External Harddrive in Mac OS

The end of the year is a great time to tie up loose ends that accumulated through the year. In the modern era, a big loose end for many of us involves computer data.

External harddrives are more affordable than ever, so there’s really no excuse for not having a physical backup of your information. Even if you have cloud storage, there’s something reassuring about a physical object that you can pick up and put somewhere safe.

Seagate and Western Digital dominate the external harddrive market. I often buy drives from these two manufacturers at Costco, which has great prices, but never offers drives that are formatted for Mac OS.

This is important, because these drives generally come out of the box formatted either with “FAT32” (which has a 4GB filesize limit – an unacceptable limitation for folks working with video files), or “NTFS” (which can be read by Mac machines, but not written to). There is something called the “exFAT” file system, which is supposed to work perfectly with both Windows and Mac, but there have been numerous reports of exFAT drives becoming corrupted by Mac OS, so I would not recommend it at this point.

The safest approach is to use the Mac OS Disk Utility to quickly format your external harddrive to work perfectly with your Apple machine. If you’ve done this once or twice, it’s easy, but the first time through, there are a lot of options to sift through. Here’s the way to do it.

1) When you open up Disk Utility, you’ll see the screen below. First, select your external drive from the list of drives on the left, and click on the “Partition” tab near the top.

disk utility screenshot 1

2) Select “1 Partition” from the “Partition Layout” drop-down menu on the left.

3) Choose “Mac OS Extended (Journaled) in the “Format” box.

4) Click the “Options” button. This will open a pop-up window like this one.

disk utility screenshot 2

5) The middle option: “Apple Partition Map” is the safest one, if you might need to access your files on older machines. Otherwise, you can click on GUID. Either one will work fine. Just make sure that it’s NOT set to “Master Boot Record,” and click “Ok.”

6) Back on the main screen, double check to make sure you’ve selected a new external drive, and not a drive with anything on it.  This is critical, because the partitioning process will wipe all data from the drive. Once you’re sure you’re working with the correct drive, click “Apply.”

That’s it! You can name your new drive either within Disk Utility, or in the Finder, once the drive has been formatted.

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