Using Disk Utility to Erase Disk-won't unmount

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.

wow this worked!!!

Option key heaven... thanks Coluch!! This worked first time for me, a total mac newbie!

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!

Every time I have a problem with a mac, you always have the best answers. it's like the 5th time you saved my ***. I'm not even sure if you're real or not. But thank you.

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

This just saved both my drive and my sanity. Thank you SO much!

I have found the easiest solution ever!!!!!

1) Eject disk from desktop

2) Open Disk Utility

3) Erase!

Ps: I've tried all the top comments before but didn't worked.

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. :-(

sadly I received this back 'Forced unmount of disk2 failed: at least one volume could not be unmounted'. Any advice on what to do next would be great appreciated.

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.

I solved this issue in a slightly different way.

1. An external Time Machine backup drive refuses to work, unmount, be reinitialized from Disk Utility.

2. Open Activity Monitor, and select the fsck_hfs process.

3. In Disk Utility, start initilizing the external drive. DU will say that it is trying to unmount the drive.

4. Immediately quit fsck_hfs from Activity Monitor.

5. With the external drive left free from fsck_hfs, DU will reinitialize it.

Paolo