Cant unmount disk mac external hard drive

The user often experiences a problem, while handling some of the Macs, when they are not allowed to repair permissions or directory in Disk Utility. They are unable to erase or partition the drive. The error, which is thrown, is the: The error occurs in such situations like formatting Mac as well as partitioning and verification and repairing of Mac disk.

The reason for this error is the modification of the boot drive, or it is being used by some other process or application. If the internal drive is causing the issue because the OS X Recovery exists as a partition on the physical disk, unable to modify or unmount the internal drive, then the preference must be given to a network drive or an external drive. Disk Utility can be run from the external drive. The version of the OS X does not matter, by at least must be The one and only requirement are that Disk Utility must reside on the drive.

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Formatting the hard drive or partition scheme will recreate new HFS file structure on the hard drive, which will be free from cryptic errors. This is the most recommended method to repair the error. Any OS X boot drive is needed to complete the task. But, the important point to remember is that the installer or the recovery drive must reside in the drive, separate from the primary boot disk with the installed OS on it. The above steps offer a resolution of the problem. The errors could have been unresolvable without a boot drive. Therefore, a bootable thumb drive was a good option.

For the older Mac OS X like The above error may also be triggered due to first Aid or while formatting a non-boot partition. In this case, a resolution of the problem occurs with the Recovery Partition, which comes with all the newer versions of the Mac OS X. However, this is not applicable for the modification of the boot disk with the help of partitions or formatting. Then the resolution lies in the previous method. Otherwise, we follow the steps: This will not work with the disk that is throwing the error is the same as the primary boot partition.

The solution lies only in using a separate USB drive for fixing the error. Vishal is a data recovery expert Stellar addressing several data loss scenarios on a macOS system. He loves to read autobiographies and his personal favourite is of Steve Jobs.

Helpful answers

View More. Please help me recover as the SSD contains important projects and documents. I suggest you to install Stellar Data Recovery Professional for Mac to recover your important documents and to avoid any data loss risk. Get data off the volume before erasing it? Great piece of advice! Worked at first attempt, I was running out of hope after trying several solutions from other forums. Thanks for the post. Forced unmount of disk2 failed: Yeah, unfortunately, no idea on that. Honestly, since that appears to be an external drive, I would shut down the computer and then just unplug the drive.

I have tried all the methods listed in previous comments. I used to have a boot camp windows 7 that was deleted a year ago If that would effect it. I am not using any external drives. After trying for several hours, came across this solution and it worked perfectly, thanks much for posting this!

Fix for disk erase failed couldn’t unmount disk – St. Ignatius College Prep Tech Blog

Either way, glad this worked. How do you know which one to choose to unmount? Disk erase failed. Type df -h and hit Enter to see free disk space but this will also show the mounted paths. I also tried it in a different command on the other page you referenced: Why are you trying to unmount Macintosh HD?

Are you booting from an external drive? The Apple instructions https: Boot into recovery mode hold down Cmd-R while rebooting and then you should be able to unmount and erase Macintosh HD. Hence this series if inquiries.


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If you really want to erase the entire disk, including the recovery partition, you must boot from an external drive. Anyway, it sounds like I should be good to go. Thanks for the help, I really appreciate it. Thank you so much! It took me an hour to find your page and I am glad that I did. You have made my day! Wanted to format it but then it still says it needs an unmounted disk.

Linux This operation requires an unmounted disk. Hi Ronald, I ran across your post and see you had the same issue im having now with no luck in finding a solution.

This was a year ago I realize but do you happen to remember how you fixed your SDcard? HUGE help! Simple solution that worked perfectly, and all the other solutions I found were very complex and would have been time consuming.

What to do when a hard drive won’t unmount in OS X El Capitan

Hello, I have the same problem and I ran into you website. I was trying to erase an external hard drive, and got this error. Following your directions, the disk was unmounted successfully in terminal. At Disk Utility, I saw the partitions of the external hard drive being greyed out. So I clicked at the hard drive and clicked Erase, but still got the same error. After ejecting it and reconnecting the drive, it seemed that nothing has been erased.

What would you suggest? Wiping volume data to prevent future accidental probing failed.


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  • When I Googled your error, this came up as a solution: Permission denied sudo: This resolve my case. Thanks a lot! It worked! I had a Mac Mini that I needed to reformat and could not get the disk to unmount.

    Erase process has failed. Click done to continue. Disk Utility Error FIX - Mac

    So I found this page and tried everything. No joy. I was able to force an unmount and could wipe the disk. Same troubles here, just trying to wipe and do a fresh install at this point. Doing the list command shows up to 15 disk images? I recovered the data via Target Disk Mode, then got stuck with the above error.

    Found this page and it was persistence that got me past the problem. It took 5 repeated attempts with a Restart after 3 goes, but eventually worked. I used this link to join them back together — http: Your email address will not be published. Subscribe Sign up for news, views and offers and more from our expert team. Posted on 7th May by Amsys. Then select the desired external drive from the startup manager screen and press the enter key.

    Also perform a permissions repair if required. Still not playing ball? At the unix prompt enter: This should unmount all volumes of the physical drive: Still unable to work on the disk? Still getting those pesky disk errors? Bit more drastic, but you can attempt to force a volume or the entire physical disk to unmount: This should force unmount the volume: This should force unmount the entire physical disk and all its related volumes: