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

Andy had the solution for me.

I have a Mac mini Server 2011 with an OWC Mercury EXTREME Pro 6G SSD

The High Sierra install balked until I ran those two commands in terminal. I'm not sure what they do or why, but the installer worked immediately after. Thank you Andy.

I have seen discussion from the OWC crowd of changing firmware on the drive, so I am stating that I did not do anything but run those two commands for the install to work. Good luck everybody.

Can you possibly tell me how to do this as if you are talking to a 3rd grader? I have purchased my first mac computer and I tried to erase it (to return it to Best Buy) and then reinstall macOS and I am receiving this error after it tries to install for about 45 minutes. I ran it twice. When I click on repair macintosh HD I get the unable to unmount error as well. I dont understand the commands you mention. How do I get to a point where I can put in commands?

My mac os doesn’t start normally.. :-( i guess something crashed my os and then i get apple logo and progress bar.. even after 100% completion its still wait there.. so i have only option of recovery mode..

I tried reinstall OS x option in recovery mode and received following error:

“MacOS could not be installed, cannot unmount the volume for repair”

I do not want to erase my hard drive/ loose any data.. plz help.. Thanks in Advance..

All good upto step 5, executing the command at step 6 gives error : “no such file or directory”..

Ok, let me give you the issue background.. one fine morning when i started my macbook it showed me grey screen with apple logo and progress bar, it completed 100% but nothing happend.. then i tried resetting pram no luck.. then safe mode but could not open... tried reistall os x via recovery mode option still same status.. tried internetrecovery as well but no luck.. then moved the kext files as mentioned in the one of the forums: https://www.justinsilver.com/technology/os-x-el-capitan-10-11-1-hanging-on-boot- fixed/

After this also no luck, again tried reinstall os x via recovery option.. and then after completion i get “cannot install macOS Unable to unmount volume for repair”..

You will need an external drive formatted as GUID and clone software to create the clone. See directions here:

Preparing your backup disk for a backup of macOS | Carbon Copy Cloner | Bombich Software

Software used to Clone:

CarbonCopyClonerhttp://www.bombich.com/download.html (All options are available free for 30 days)

SuperDuper!http://www.shirt-pocket.com/ (Free forever to do an erase and install. Purchased version allows for smart updates and schedules)

SUGGESTIONS FOR EXTERNAL DRIVE

The 3TB or 4TB drive is often the best buy. You can partition large drives to use for multiple purposes.

Check out the Western Digital and Seagate drives. Comes Mac and/or PC. Get the one that is cheapest. Format with Disk Utility to use on the Mac and not use the WD software. Prices vary so check first.

Check the warranty when comparing drives. The longer the warranty the better the drive. Look for a drive with a 2 or 3 yr warranty.

BestBuy, Staples, Office Depot will match Amazon pricing.

Current best buys on Amazon

WD 4TB Black My Passport Portable External Hard Drive - USB 3.0 - WDBYFT0040BBK-WESN

3TB $95.99

4TB $109.99

Comes in colors

http://www.amazon.com/dp/B01LQQH86A/

WD 4TB Elements Portable External Hard Drive - USB 3.0 - WDBU6Y0040BBK-WESN

This drive is smaller and does not need to be plugged in to electrical. Runs off USB

http://www.amazon.com/dp/B017IGERDE/

3TB $88.95

4TB $107.00

WD 4TB My Book Desktop External Hard Drive - USB 3.0 - WDBBGB0040HBK-NESN

http://www.amazon.com/dp/B01LQQHL4E

4TB $97.99

Seagate Backup Plus Slim 2TB Portable External Hard Drive USB 3.0, Black (STDR2000100)

Comes in colors

http://www.amazon.com/dp/B00FRHTSK4

2TB $68.80

4TB $106.99

Seagate Expansion 2TB Portable External Hard Drive USB 3.0 (STEA2000400)

http://www.amazon.com/dp/B017KE8OG0

2TB $69.99

4TB $109.99

Don't get a WD My Cloud drive. Does not work well with clone and Time Machine.

USB 3.0 drives work on USB 2.0 but you do get 2.0 speed. They are cheaper because they are popular PC drives. If you get a new computer you'll get the bump to 3.0 speed. I don’t recommend FW. The newer computers don’t have FW ports. You would need a connector in order to use the drive on a newer computer.

Hey Andy the link you give does not work, I have a MacBook Pro early 2015 and have completed tried to reformat but when in disk utility I try to first aid it says"unable to unmount volume for repair" I tired everything. I really need help

Hi Andy, so I’ve read thru this thread, and still not grasping this.

I can’t load into OS because it goes straight to the high Sierra install where it wil fail and say restart. So I’m limited to within in recovery mode. I can not do a time machine restore, clean install or anything. Can’t inking the drive. My question is can the commands you got from Apple be used in recover mode in terminal? If so then what. Do I let it restart and do the install or do I stay in recovery and install from there? Appreciate any help from anyone on this

Hi thanks for the reply. I’m aware that is a option. I’d be fine doing a clean install cause backed up the problem with this option is I don’t know how to force homing the drive in terminal in recovery mode. The drive is there and as other people in this thread have had the sand problem but they were able to force it to unmount but I don’t know what I’m doing wrong in terminal. Otherwise I’m not able to erase the drive at all. Even in recovery installing new OS it doesn’t see the drive or to do a time machine restore I can’t skectes my drive. From what people said in this thread it’s something the high Sierra installer screw up with a glitch.

Just to be clear, while in Recovery Drive > Disk Utility, you can't unmount the internal Macintosh HD to erase the drive.

In Recovery > Disk Utility, unmount all external drives.

In the Terminal type

diskutil list

This will get a list of your drive.

The output will look something like this:

Dianes-iMac:~ diane$ diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *121.3 GB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_APFS Container disk2 121.1 GB disk0s2

Using the info for your drive, use this command to unmount.

diskutil unmount /dev/disk0

If the drive still fails to unmount, it's possible that the drive is failing. Often Spotlight cannot let go of a failing drive. Not sure if disabling Spotlight while in Recovery will help, but it's worth a shot.

sudo mdutil -a -i off

If this fails, I would attach an external drive that is formatted as GUID. Select to install macOS to the external drive. You will boot from the external drive in a new High Sierra install. It will be formatted as HFS+ since it's a rotational external drive. While you are booted from the external you can try erasing the Internal drive. You might find this will give you more options than while booted from recovery.

This is so annoying. I still can’t get this thing to unmount. Unmount of disk0 failed: at least one volume could not be unmounted

Can’t do anything. can’t delete my drive, can restore or install in recovery.

As I mentioned this could be a sympton that your drive is failing. Have you considered doing the install on an external drive? This would allow you to recover any data off your internal drive as well before erasing.

So finally managed to get things going. My bad, I’m such a burn out, I was attempting to do all this in recovery mode, finally realized my error and went into internet recovery mode and then I was able to get things rolling. Ran first aid, said drive had errors, ended up just wiping the the whole drive and doing a restore from time machine. All good, restored perfectly everything working, however, upon reboot and it all loaded up and the high Sierra installer was still there cause it was downloaded when I backed up before attempting install. So I thought why not, I’ll try the commands everyone been using here in terminal but both commands say no such file or directory so as it stands now I don’t think high Sierra is not meant to be for me. Sierras been working fine all this time. Apple defiantly not on there game with this version of operating system.

Sadly, no joy. Did Andy's suggestion help everyone else here - or are there those who are still stuck, not being able to unmount and erase?

Have dual drives in my 2012 Mac Mini - HDD with Sierra and Server on it (the original start up disk), and a Crucial SSD - installed Sierra on it, and transferred all across.

BOTH drives working as expected - but cannot unmount HDD to erase, and cannot update SSD to High Sierra, on account of both not unmounting.

The suggested Terminal commands (in Terminal on either drives, or in Terminal through Recovery Mode), do not make any difference. Still met with the same error message.

I had no luck either but had backups so once I did internet recovery I was able to wipe the drive and I just put normal Sierra back on and gave up on high Sierra. So if you got backups and your fine with Sierra I would say internet recovery (Command (⌘) – Option (⌥) – R ) then you should be able to wipe the drive and go from there.