Mac OS Sierra - Disk Utility will not let me partition an external hard drive

Solution 1:

I've just encounter the same problem, where Partition icon is grayed out. I found the solution.

Simply launch this command in terminal and the partition icon will not be grayed out anymore :

diskutil erasedisk hfs+ External GPT /dev/disk2

For clarity, in the above command, the path argument starts from /dev, not "External GPT "

However, this command will erase the disk, make a backup if needed before !

Source : Apple Discussion - Alberto Ravasio

Solution 2:

The sample screenshot in the question is only showing "Volumes", not "Devices".

In Disk Utility, select "View" and "Show All Devices" to also show the device hierarchy.

Then, erase the device - doing which will reset the MBR.

(Click "Show All Devices" will allow other formatting options thus enabling the partition button)

Solution 3:

• In the disk utility, select 'View' and 'Show Devices'.
• Select the drive (out-dented entry with the mfgr.'s ID and size) from the side list.
• Click on the Erase tab in the Disk Utility toolbar. A panel should drop down.
• In the drop down panel set the partition scheme to GUID. Set the Format type to Mac OS Extended (Journaled.)
• Click on the Apply button and click on the Done button when it is activated.
• You can now create partitions.

Solution 4:

TMWP: Yes, that's what I did. Here's the procedure:

• Go to System Preferences > Time Machine, and turn Time Machine off
• Make sure that TM disk and your temporary storage disk are both plugged into your computer's USB ports
• Launch Disk Utility
• Click on 'Restore'
• Set the source to your old TM disk
• Set the destination to your temporary storage disk
• then start the process

This will copy your TM backups onto your temporary storage disk. Make sure the copy is complete before going further, as the subsequent partitioning of the original TM disk will erase all data on that disk.

Then reformat your original TM disk to create multiple partitions. When the partitioning is complete, you can restore the TM backups from the temporary storage disk onto the new partition where you want TM to reside.

Finally, in System Preferences > Time Machine > Select Disk, select the new partition as TM's target. TM can then be turned back on.