4 Replies Latest reply: Apr 30, 2015 2:37 PM by Grant Bennet-Alder
Nick Howard Level 2 Level 2

I'm trying to install a Western Digital caviar black 2TB as the fourth internal drive in an early 2009 MacPro running 10.7.5.


I'm using Disk Utility to format it - or trying to.


I click 'erase"


Helpfully, it tells me that this disk is unformatted.


I click "erase"


I get:


"Disk erase failed with the error:

Couldn't open device"


Could anyone tell me how to deal with this?

  • Nick Howard Level 2 Level 2

    I have sorted this, but randomly. I restarted a couple of times and managed to erase the disk. But it only appeare4d greyed-out in the finder. I gave it a single partition, and then erased that, and, lo and behold, I had a disk on my desktop. Dunno how it worked or whether it will continue to do so, but fingers crossed...

  • wham1000 Level 1 Level 1

    Restart pushing shift to safe mode. Then format.

  • Robert Rose1 Level 1 Level 1

    Yes, this worked for me.  Thanks


    This was a drive that had been used as a Time Machine, and I wanted to erase the time machine files and repurpose the drive. 

  • Grant Bennet-Alder Level 9 Level 9

    This information does not pertain to the original Poster's problem, but is being added for folks who get here by searching.


    Internal drives OVER 2.2TB have a different problem with ERASE after 10.8.4.


    Mac OS X wants to create a Logical Volume group on them, but the rest of Disk Utility does not understand how to further partition it, and it becomes "stuck".


    Solutions include:

    • ERASE in an External Enclosure modern enough to deal with drives over 2.2TB

    • Use Disk Utility in any version older than 10.8.4, including the Disk Utility on the 10.6 Installer/Utilities DVD (provided your Mac can boot from the 10.6 DVD)

    • Use command line diskutil to delete the Logical Volume Group and the Logical Volume. This may require two terminal windows open to cut and paste the long UID strings from diskutil list in the other window.