Using Disk Utility to Erase Disk-won't unmount

Thanks to Dana for the pkill tip and to everyone else for their suggestions here. I couldn't find fsck_hfs in the Activity Monitor. Booting into recovery mode wouldn't work for me either.

The process that sorted it for me was:

- Disable spotlight indexing in terminal using sudo mdutil -a -i off

- Stop fsck_hfs process in terminal using sudo pkill fsck_hfs

- Immediately open Disk Utility and Erase the volume

- Re-enable spotlight indexing in terminal using sudo mdutil -a -i on

Cheers,

Chris

I am having similar issues and it's really frustrating, restarted command R, erase disk failed, restarted went to disk utility

tried to erase the disk from there but it's all greyed out. Repaired disk permissions, disabled spotline via terminal, still greyed

out. I used several commands listed on here in terminal

diskutil eraseDisk JHFS+ My\ HD disk0

diskutil eraseDisk JHFS+ UntitledUFS disk2

But it won't unmount the disk, I'm using Yosemite and no matter what I do it won't let me erase

the disk on here, help?

Thank you for your suggestion! So far, it appears to have addressed the issue on my mid-2010 MBP (running 10.10.2), and my (USB) WD 500G EHD Time Machine back-up is once again visible/available in the Finder (and in the process of backing-up ~200G). The only real downside of doing this AFAIC was losing all of the previous back-ups on the EHD, but it's worth it (to me) if this proves to be a permanent fix.

FWIW, A Potential Source of the Issue:
While the EHD was engaged in its Time Machine back-up yesterday, I was simultaneously backing-up some of my files onto multiple thumb drives. This reinforces my suspicion that there exists some type of "simultaneous, multiple back-ups" conflict with Time Machine. On multiple occasions I've experienced similar issues with simultaneous Time Machine and thumb drive back-ups, and, except for this time, the disastrous result reported by Disk Utility was always the same: a damaged HDD (_not_ the EHD) that could only be repaired by erasing it. (As I recall, the Disk Utility error citation--paraphrased--indicated that the # of files were not identical as they should have been.). Based on my research in other Apple forums, Time Machine has been notorious for causing all kinds of strange problems. Has anyone else been able to pinpoint what may have been done to cause the EHD damage/corruption that caused it to malfunction and its Finder icon to vanish? I'm keeping my fingers crossed that all will still be well once the back-up is complete and I re-boot, and I'll report back if I experience any issues, so, hopefully, you won't hear from me again on this topic. ;-)

Nothing worked in my case. No matter what, the disk would not unmount or reformat. What did work was bootcamp. Since my Windows volume was on another drive, I was still able to mount and reformat the drive as NTFS. After the bootcamp reformat, I was able to restart and format the disk to Mac OS from the recovery menu.

This was the technique that solved it for me. The other solutions above might have worked for me if I knew anything at all about Unix code and Terminal, but for a novice the easy way was: sudo diskutil unmountDisk force /dev/disk<number> Thank you eplt@odw

This was perfect for me. After the 10.10.3 update, my backup stopped working. Time Machine couldn't access the hard drive. I could not get it to unmount so I could just reformat and start Time Machine fresh. This solution finally resolved and allowed me to unmount and erase the drive. Thanks

Unfortunately absolutely none of the solutions discussed in the various responses have worked for me with a WD My Book Studio which worked fine with my old MacBook Pro but never with my mid 2014 MacBook Pro running 10.10.4. I also tried WD so-called solutions and apps, none of which worked and in fact the installation of their apps seemed to go OK but these just disappeared and could not be found.

I did not try the bootcamp advice since I have no idea what that is.

Really fed up. Will stick to LaCie drives from now on!

This helped me, I was searching around for ages trying to find the answer. I could tell the disk was doing 'something', turn out to be a fsck.

Made we wonder if there was a way to understand what processes were working with a particular device, you can use something like:

sudo lsof | grep '/Volumes/Macintosh HD'

This shows the open files on the device which could indicate to a rogue process?

None of the above suggestions worked for me. For instance,

sudo diskutil erasedisk JHFS+ Untitled /dev/disk4

Password:

Started erase on disk4

Unmounting disk

Error: -69888: Couldn't unmount disk

This is a LaCie XtremKey USB 3.0 that does not mount and cannot be formatted after the Mac Finder showed "Disk not ejected properly” (yet nobody ejected if, of course; it did it spontaneously) while saving a file to the pendrive. Any idea? Thanks.

Huge thanks to Holmes321 and Dana 刀!!!!

My laptop is early 2008 MBP (runs 10.10.5) , and I use LaCie 2TB external hard drive as my time machine. I only do back up once a month. But 3 days ago, when I wanted to do back up, I found out there is no icon of my time machine disk on the screen, but I could see it in Disk utilities.

After I read some discussions here, I tried everything here mentioned. But for the people like me, who have a very little knowledge about computer, some words which people said here, I am difficult to understand and follow. (I did ask a friend to help me to understand how to follow these steps).

Finally, after all of tryings failed, (really I did try everything here the people mentioned), which always give me the same info "couldn't unmount disk". I found out "Holmes321" who wrote every step very clear. I followed what he said, wow, it finally worked! Now I have reformatted my external drive!

Massive thanks!

Thank you very much! I tried killing spotlight, but that didn't do anything. Following your instructions is what did it. I would've never known how to force unmount a disk through Terminal otherwise!

HI to all, i have the sampe problem here. It's so frustated. My basic is not an it, i'm just a normal user doesnt understantd any programing language. Can anybody please help to guide me? 😟

ps : i already tried what you guys tell in here, go to terminal.. But i dont get it, which one is process number (sorry this is not my expertise) 😟 i'm just a noob

thank youu

E R

Thanks.... but I doesn't wish to work for me. I'm in Target Mode, my other macs sees the affect drive. I have Terminal open drop in the lines, head back to DU, hit erase and I get the same "Couldn't unmount disk" issue. :-(

Thank you 🙂 .. those were the terminal commands I was looking for (similar "unable to unmount partition" problem (not Spotlight-related though). Once the disk was unmounted, I was able to use Disk Utility to Repair the disk (reported as ok though 😕 ), and, from there, Disk Warrior to rebuild the directory (again, nothing serious found, but, what the heck.. the combination of all that worked for me 😉 )

Thank you for helping solve this. I too was trying to resize partitions on a backup drive (so not working with the booted drive). Turned off Spotlight but problem persisted until i discovered a process called distnote that was listed in Activity Monitor, right under the diskutility process (if sorted on process name). Force quit on distnote and Woohoo! my un-demountable drive is free to play. Thank you, I was beginning to think I'd have to call for professional help.