High Sierra install fails - "unable to unmount volume for repair"

I have the exact same issue with a late 2016 27-inch iMac with 1TB SSD. I've tried disk utility repairs both in Sierra, while in the High Sierra installer, and by booting into recovery mode. I've also re-downloaded the installer several times. I had no issues upgrading on my older iMac, 15-inch Macbook pro with touchbar, or VMs.

Relevant snippet from the logs:

Sep 27 15:32:48 Hostname OSInstaller[560]: The volume 3AC2B122-F459-4D4D-9D57-6FD3735A61C8 appears to be OK

Sep 27 15:32:48 Hostname diskmanagementd[562]: diskmanagement: rawLaunch_block_invoke: waitpid(2) pid=586 ret/errno=586/35 status=0x00000000 exit=0

Sep 27 15:32:48 Hostname OSInstaller[560]: Storage system check exit code is 0.

Sep 27 15:32:48 Hostname OSInstaller[560]: Repairing file system.

Sep 27 15:32:48 Hostname diskmanagementd[562]: diskmanagement: [DMToolMountMisc _DAOperation_performsync_:disk:options:mountpoint:arguments:asEUID:asEGID:timeo utSec:dissenter:dissenterPID:]: [un]mount failed: err=-69888 un0mt1=0 timeout=0 dissenter=1 dissenterpid=0 dissenterstatus=49168=0xc010

Sep 27 15:32:48 Hostname OSInstaller[560]: Volume could not be unmounted.

Sep 27 15:32:48 Hostname OSInstaller[560]: Restoring the original state found as mounted.

Sep 27 15:32:48 Hostname OSInstaller[560]: Disk repair retry failed too many times. Will hard fail.

Sep 27 15:32:48 Hostname OSInstaller[560]: Clearing automation and attempting to rebless. source volume: SKCSDisk { CSLV UUID: F9058AC2-96C9-44DA-8889-926055B945FF CSLVG UUID: 3AC2B122-F459-4D4D-9D57-6FD3735A61C8 BSD Name: disk1 Mount point: /Volumes/Macintosh HD Role: kSKDiskRoleMacSystem Type: kSKDiskTypeCSLV } rebless: 8B9F5F16-6CFA-3E48-ACAA-4EF7ADC213B5

Sep 27 15:32:48 Hostname OSInstaller[560]: OSIInstallElement <OSIRepairDiskElement: 0x7f9e55ba1300> errored out:Error Domain=com.apple.DiskManagement Code=-69673 "Unable to unmount volume for repair." UserInfo={NSLocalizedDescription=Unable to unmount volume for repair.}

Sep 27 15:32:48 Hostname storagekitd[561]: storagekitd: copyDiskForPath returned nil, error: -69808

Sep 27 15:32:48 Hostname storagekitd[561]: storagekitd: copyDiskForPath returned nil, error: -69878

Sep 27 15:32:48 Hostname OSInstaller[560]: ------- Install Failed -------

Sep 27 15:32:48 Hostname OSInstaller[560]: Operation: Verify and repair disk failed, Failure Reason: Error Domain=com.apple.DiskManagement Code=-69673 "Unable to unmount volume for repair." UserInfo={NSLocalizedDescription=Unable to unmount volume for repair.}

Ditto on my 2015 Macbook Pro. Created a USB stick with High Sierra, booted off that, ran Diskutil against the SSD on the laptop, no errors reported, but can't unmount the disk there too. Entered the terminal, did a diskutil unmount /dev/disk21, failed with a UID=0 voted no (or something like that) error and didn't unmount the disk.

Next I tried a diskkutil unmount force /dev/diskk21 command, that got the device unmounted. Ran disktuiil volumerepair on it now, no errors.

Rebooted back to the ssd, tried the install again. Same error. ARGHH.

Next step is to take a fresh time machine backup, wipe the disk, install High Sierra on it, then restore from the backup. What a PITA.

I've tried everything short of booting off of a linux thumb drive and zeroing the hard drive on my 2012 Mac mini. I can't even get it to let me force an unmount of the hard drive in order to check the disk for errors.

For the record I'm booting off a USB installer I created for High Sierra

I had "success" by doing the following:

1. Boot into internet recovery mode Option-Command-R

2. Open Terminal and force unmount the drive

•diskutil list

•diskutil unmountDisk force /dev/disk<number>

3. Open Diskutil and reformat the drive to APFS ****Note that you will lose any data stored on the drive****

4. Install High Sierra

I tried disabling time machine, running disk recovery, re-installing Sierra through recovery mode (failed / file unavailable), re-installing High Sierra via recovery mode (installer failed), installing Sierra via a USB drive (hold down option, select USB drive with image on it), and probably something else I'm forgetting to mention.

I had intended on further testing/troubleshooting how to get this to work without blowing away my install but my TimeMachine backup (took 12+ hours to restore) somehow prompted me for the wrong Apple ID (I had changed mine about a year ago) and wouldn't let me progress with the restore past that.

Given the time I've spent trying to fix this it is ultimately faster to just flatten and re-install.

Interesting I tried to do the force unmount and I got an error saying that the force failed...

I'm trying to zero out the drive. I imagine I'll have luck because I will be able to repartition/reformat the drive to APFS

First Aid from a booted drive cannot fix all problems. You must be booted from an external drive in order to fully repair a drive.

Something is running on that drive that is not allowing you to unmount. First disconnect any external drives then try booting into Recovery Drive and see if you can run First Aid now.

If you still have problems, how comfortable are you using the Terminal? See this link for help unmounting.

http://osxdaily.com/2013/05/13/mount-unmount-drives-from-the-command-line-in-mac -os-x/

So, did the same thing. Loaded from backup external drive... it failed also. Chatting with Apple Support, they told me to me to either 1) do a full reinstall from a clean disk or 2) wait for a software update to fix the problem. They know there is a software (i.e. not a hardware) problem.

Tks Bill

I also have the same issue with a Late 2012 Mac Mini i7 Server that I have installed an Intel 540s 1TB SSD as the boot drive.

Something else to note is that when you quit the High Sierra install and restart to Sierra, TRIM is disabled on the SSD and needs to be re-enabled with "sudo trimforce enable" from terminal.

I have just tried the new release of the High Sierra installer 13.0.66 and still have the same issue.

So, I did this, as well (reformat drive in Disk Utility to APFS and install High Sierra from scratch). However, when I went to restore user data and applications from my Time Machine backup, it said it couldn't find a usable volume. Have you seen this message, too?

Joe

I also have a 2012 (late) Mac Mini, with stock Apple SSD, running 10.12.6, and FileVault off. Same issue.

Disk Util reports no drive issues. Have tried a couple times from normal reboot and safe reboot. Reaches the same point (only a couple minutes into install) and reports message "Unable to unmount ... please quit installer and try again".

Also deleted and downloaded the installer on the chance from the time I originally tried Apple updated the installer. Last version of 'Install macOS High Sierra' I tried was 13.0.66.

Turn off Time Machine in System Preferences.

Remove all external devices.

Restart in safe boot mode.

Try running the installer now.

Follow these steps to start up into safe mode.

1. Start or restart your Mac.

2. Immediately after you hear the startup sound, press and hold the Shift key.

3. Release the Shift key when you see the Apple logo appear on the screen.

Have 2 Mac Minis.

Update worked well on a

- MacMini, 8GB, 500GB HDD, middle 2011,

but not on a

- MacMiniSercer, 16 GB, 1TB SSD + 1 TB HDD, late 2012

Of course, hard disks are error free.

Hope that Apple will solve the problem soon. Seems to be a MacMini related problem ?

Same config here. Same error. Tried Apple Support - no luck. They suggested taking my iMac into an Apple Store (I'm lucky enough to have one within 20 miles). Not exactly the most portable of machines.

Building upon previous answers, I have concluded that the problem is because the installer is glitched and can't convert the drive to APFS. This problem can easily be circumvented:

1 . Boot to internet recovery or a USB drive with the High Sierra Installer (standard Sierra recovery mode won't do).

2 . Go to Disk Utility and mount your Mac volume.

3 . Close Disk Utility and go to the command line terminal.

4 . Do diskutil umount force /Volumes/Macintosh HD/

Take note of your disk id. disk1 in my case.

5. Run diskutil apfs convert /dev/disk1s1

(replace disk1 with your disk id if needed)

6. Once this is done, reboot and High Sierra can be installed from either a USB drive or Internet Recovery mode (option+command+R)