iMac 2017 can't reinstall High Sierra

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Level 1

8 points

iMac 2017 can't reinstall High Sierra

Hi everyone

I need some help. A friend bought second hand an iMac 2017 27" with fusion drive. The guy who had it said he formatted the disk before giving it to him. When my friend open the computer it started on the install screen. He selected to reinstall the OS but it said that it couldn't. He tried to format the disk, it showed a "Fusion Drive" as a device and another disk as a volume. The device has greyed out the erase button. The volume can be erased. When I went there, I brought a usb with 10.13.2 that I made a while ago for my computer and I knew it was good, it worked. I put the usb on, restart with "option" key, boot from my usb and format the disk as APFS. Now there is no separated device and volume, there is just one disk. I start the installation, but when it reaches the drive to install, the disk is greyed out, showing a message that the OS can't be installed, and I should get more info on this site: APFS Fusion. I go back and the disk won't format to anything but APFS. So I click on partition, create a volume, format it as HFS+ and go back to installing. This time the disk was available, I selected it and the installation started. However after 2-3 minutes a window popped up, saying there was an error and I should try later...

I'm very confused, I never had an issue like that. As a final solution, I formatted again the drive as APFS, then restarted the computer pressing option + command + R to start Internet recovery. It started fine but after like an hour the same message appeared again.

Does anyone have any idea what I should do?

Posted on Mar 17, 2018 2:06 PM

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Answer 1

Best reply

Manolis_from_Prague

Level 2

163 points

Mar 18, 2018 7:31 AM in response to spyros_1

To make it absolutely clear when you want to use Fusion Drive on 10.13.x High Sierra never go APFS, because as I said before APFS is not yet supported for Fusion Drives!!!

Your attempt where you went back to HFS+ as you described before seems like you simply had just internet connection problem. So to mitigate this, make sure you have your USB installer. These days there is vesrsion 10.13.3 out.

Create a bootable installer on external drive using createInstallMedia.

Full steps at How to create a bootable installer for macOS - Apple Support

sudo /Volumes/InstallAssistant/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/<external drive>

where <external drive> is the name of the drive where you wish to create a bootable installer.

Note: createInstallMedia will erase the selected volume.

Restart iMac with your USB macOS High Sierra Installer while holding ⌥ key.

When ready go into menu Utilities > Terminal and with 'diskutil list' once again confirm which of your internal physical drives is SSD and which one is HDD. (Last time there was disk0 28 GB SSD and disk1 1 TB HDD) but this can change whenever you Restart your mac in different conditions.

Your Logical Volume on Core Storage should be at disk3 (but check it again, to make sure)

Now unmount all those disks in sequence:

diskutil unmountDisk disk3

diskutil unmountDisk disk1

diskutil unmountDisk disk0

Discard everything including GUID partition tables on both of your physical internal drives:

gpt destroy disk0

gpt destroy disk1

Check that there is no CoreStorage nor APFS anymore:

diskutil cs list

diskutil apfs list

Restart again from USB Installer

Go back into the Terminal and confirm once again with 'diskutil list' the sequence number of your SSD and HDD drives and also that they are now completely clear of everything. (This time probably 28 GB SSD should come as disk0 and 1 TB HDD as disk1) If it is like that continue with creating new CoreStorage or adjust disk number according to your situation:

diskutil cs create "Macintosh HD" disk0 disk1

Note: Once again disk0 (Faster SSD) have to come first then disk1 (Slower HDD) as second.

Now you should have "Macintosh HD" Core Storage ready but you need also to create your Logical Volume with same name "Macintosh HD":

diskutil cs createVolume "Macintosh HD" jhfs+ "Macintosh HD" 100%

Now disk should be ok exactly the state as it comes from the store. Quit from Terminal to macOS Utilities and you can proceed with Reinstall macOS (from your USB Installer not from the Internet to mitigate Internet connection problems).

This is it, give it try and let us know, good luck, bye...

Manoli

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Answer 2

Mar 19, 2018 4:41 AM in response to spyros_1

Side Note: I forgot to mention...

Before your next attempt to start new clean reinstallation of macOS

It's always good idea first to reset the SMC (System Management Controller) and then also reset the content of NVRAM or PRAM. That way you will make sure that NVRAM is clear of confusing settings from previous user and also from your previous unsuccessful reinstallation attempts (things like misleading efi-boot-device settings, etc.).

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Answer 3

Mar 17, 2018 2:52 PM in response to spyros_1

Hi,

because you have iMac with Fusion Drive, you won't be able to use APFS for your macOS start up disk as it is not supported for Fusion drives, yet. To find out what is the problem with your drive in your iMac, go once again into Internet Recovery and from menu open Utilities > Terminal then run following command:

diskutil list

Then post output here.

Manoli

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Answer 4

Mar 18, 2018 6:58 AM in response to spyros_1

Hi again,

I can see on the output you have in your iMac 28 GB SSD on disk0 and 1 TB HDD on disk1.

There's CoreStorage across disk1s2 and disk0s2 and on this Fusion you have logical volume disk3.

It would be ok, just disk0s2 as it comes from faster SSD should be listed first in the Fusion, I don't know why you have it listed as second one. Can you post also output of the following command?

diskutil cs list

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