All external USB disks can be formatted to work on Mac OSX, but not always straight out of the box.
In this tutorial we look at formatting disks via the GUI app called Disk Utility and its equivalent command line tool diskutil. This will work in all modern versions of Apple Mac OSX including 10.9 Mavericks, 10.8, 10.7 and 10.6.
Initially external disks may be formatted for Windows and after you connect it to your Mac it appears in the device list in the Finder, but is a read only disk meaning that you can’t write to it in its current format.
There may be other ways to resolve this issue but the easiest way is to erase the disk and set it up with a GUID scheme. This will allow Apple's Disk Utility to create its own volumes. Remember if GUID is not an available option then Show All Devices in the upper left is not selected as shown in the beginning of the article. Disk Utility’s left pane shows the storage devices connected to your Mac. Underneath each device are the drive’s partitions. There’s a third selection you need to make called Scheme. Once you’ve copied your data, go to /Applications/Utilities and open Disk Utility. If you are using the Mac OS X Installation disc as the startup disk, click on the Utilities menu and select Disk.
![Scheme Scheme](https://help.apple.com/assets/5A71F63F680CE218781BBA2A/5A71F641680CE218781BBA32/en_US/77f9b077f3eb799c3e4559180c73e75b.png)
After you determine the volume you need to repair, all you have to do is simply write this command (make sure you replace drive name with the actual name of your volume): diskutil repairvolume /Volumes/drive name Furthermore, if you want to repair your Mac's hard drive, then you can type. Diskutil repairvolume /. Sadly, Disk Utility has been made progressively worse in recent versions of the Mac OS (macOS or OS X or whatever). Usually, as mentioned already, the correct scheme is GUID. You only need MBR if you will be talking to the drive using older versions of Windows (XP and earlier if I remember correctly), and only need the old Apple scheme when using early versions of Mac OS (pre-OS X?).
The when the disk is selected in the finder bottom left symbol with the crossed out pencil means that the disk can only be read not written to. Why this is, is because they come formatted as Windows NTFS drive which OSX can only read, so we need to reformat them so we can read and write – thats where a handy utility called Disk Utility comes to the rescue.
Disk Utility
Disk Utility is found in /Applications/Utilities/Disk Utility.app, open it and select your external disk in the list on the left.
There are 2 items (or more) for each disk, you have the actual disk and the volume of the disk, the example below has the Disk Named 2 TB WD Elements and the Volume is named Elements, this example uses the Volume which will in turn also format the Disk.
Then below you will see the Format type which will be NTFS or possibly MS-DOS (FAT), we need to reformat the volume and make the format Mac OS Extended (Journaled).
Reformatting the Disk
Still with the external disk selected in Disk Utility go to the Erase tab, select Mac OS Extended (Journaled) from the format dropdown, choose to name the disk and then click Erase.
And there you have it one read and writable disk ready for OSX.
The Security Options option next to erase can control how the disk is erased by zeroing out all the blocks on the disk, this then make it impossible to salvage any previous data, with new disks this is not necessary.
Also the other format option Mac OS Extended (Case-sensitive, Journaled) in the dropdown would allow you have same name files or folders in the same location with a mix of case like ‘red’ and ‘RED’, this is popular in the Linux disk format and also possible on OSX but not the default on OSX shipped disks.
Doing it on the line
You can also do this using the command line using the tool diskutil which is the command line interface to Disk Utility, launch Terminal, Applications/Utilities/Terminal – to see a list of your disks:
and the results are similar to:
This gives us a lot of information including the disk identifiers, size of disk and partitioning scheme. So in this example we will reformat the actual disk, disk2 using the command:
Here the command diskutil eraseDisk does the erasing, format is expressed as JHFS+ which is the Mac OS Extended (Journaled) and disk is named BackupMaster and the actual target disk is defined by its identifier disk2. The Terminal will result in this output:
And there you have it one formatted disk ready to go.
WARNING: Formatting will erase all data on the device. Back up all your data before proceeding.
Instructions below are for 10.11.x (El Capitan) and 10.12.x (Sierra)
1. Double-click on Macintosh HD - or in the Finder menu clickFile > New Finder Window
2. Click the Applications folder - if using a Finder Window Applicationswill be in the left side menu.
3. Click the Utilities folder.
4. Double-click Disk Utility.
5. On the left side of the window are the drives connected to the computer. Select the capacity of the drive respective to the one containing the device you wish to format then click the Erase tab.
Example: If the drive is called 'NO NAME', directly above that, you should see the drive capacity of 'XXXX'. Select this capacity.
6. Verify Volume Format is set to MS-DOS file system or exFAT, Scheme is set to “Master Boot Record” (Do NOT select GUID Partition Map) then click Erase.
2. Click the Applications folder - if using a Finder Window Applicationswill be in the left side menu.
3. Click the Utilities folder.
4. Double-click Disk Utility.
5. On the left side of the window are the drives connected to the computer. Select the capacity of the drive respective to the one containing the device you wish to format then click the Erase tab.
Example: If the drive is called 'NO NAME', directly above that, you should see the drive capacity of 'XXXX'. Select this capacity.
6. Verify Volume Format is set to MS-DOS file system or exFAT, Scheme is set to “Master Boot Record” (Do NOT select GUID Partition Map) then click Erase.
Instructions below are for 10.13.x (High Sierra)
1. Open Disk Utility. Please See Answer 20985: How to access Disk Utility macOS
2. In the top menu bar, go to View, and choose Show All Devices
2. In the top menu bar, go to View, and choose Show All Devices
3. Select the upper level of the drive you would like to format and click the Erase button
Disk Utility Erase Scheme
4. Choose how you would like to format the drive
- Enter a Name for your drive
- Choose exFAT or MS-DOS (FAT) for the format
- Choose Master Boot Record for the Scheme
- Click Erase
5. When finished, the drive will be formatted and repartitioned successfully. Click the Done button
NOTE: exFAT is used on SDXC card (64GB and higher).
NOTE: exFAT can be used on flash drives or memory cards to transfer files larger than 4GB.
Mac Format Utility
NOTE: MacOS 10.6.2 or higher is required for exFAT file system. Some older operating systems must have a patch installed before they can use the exFAT file system.
NOTE: If the above steps do NOT resolve the problem or if the lock switch is missing or broken, please back up your data and request a replacement using our online web form.
Mac Os Disk Utility Download
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